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• Hide fields in Django admin

  - by jwesonga

  I'm tying to hide my slug fields in the admin by setting editable=False but every time I do that I get the following error: KeyError at /admin/website/program/6/ Key 'slug' not found in Form Request Method: GET Request URL: http://localhost:8000/admin/website/program/6/ Exception Type: KeyError Exception Value: Key 'slug' not found in Form Exception Location: c:\Python26\lib\site-packages\django\forms\forms.py in __getitem__, line 105 Python Executable: c:\Python26\python.exe Python Version: 2.6.4 Any idea why this is happening

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• How can I simply "run" lisp files

  - by Annan

  Python When I learned Python I installed it on windows with a nice gui installer and all .py files would automatically run in python, from the command line or explorer. I found this very intuitive and easy, because I could instantly make plain text files and run them. Lisp I'm starting to learn lisp and have decided (from reviews) that SBCL is not a bad lisp implementation. Is there a way to setup SBCL to run .lisp files as easily as with Python? Are there other lisp implementations that have this?

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• suggest me some project............

  - by anshuman

  please suggest me some project on python or perl

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• vi script problem on autocmd

  - by schemacs

  I want to create a template for all my python scripts using this autocmd bufnewfile *.py so ~/.vim/templates/python_skeleton.txt the content of python_sekleton.txt is as simple as this: #!/usr/bin/python # -*- coding: utf-8 -*- print 'Hello World' but vi give error message when i start to edit a new python script: line 2: E488: Trailing characters: # -*- coding: utf-8 -*- line 4: E488: Trailing characters: print 'Hello World' it seems '#' is not escaped,and anyone can work it out?thanks i advance

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• What's the best way to access Neo4j from Django?

  - by abdel

  it seems that i found something that let me confused; i've found two Neo4j to download to python, the first one is: http://pypi.python.org/pypi/neo4j-embedded and the second one is: https://svn.neo4j.org/components/neo4j.py/trunk/ what's the difference between the two? the first one seems to be big (size), so does this mean that if i use it i'll not need the neo4j community release (milestone)? when i've installed the first one, and tried to test a django example, it seems that the directory named "model" https://svn.neo4j.org/components/neo4j.py/trunk/src/main/python/neo4j/model/ is missing? so what's the difference, and who will be better to use with Django? and what about that one? http://pypi.python.org/pypi/neo4django/

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• Error with swig: undefined symbol: _ZN7hosters11hostersLink7getLinkEi

  - by Eduardo

  I'm trying to make a python binding for the this library: http://code.google.com/p/hosterslib/. I'm using swig, heres is the code: %module pyhosters %{ include "hosters/hosters.hpp" %} %include "hosters/hosters.hpp" I run "swig -c++ -python -o swig_wrap.cxx swig.i" and I compile with "g++ -O2 -fPIC -shared -o _pyhosters.so swig_wrap.cxx python-config --libs --cflags -lhosters -lcln -lhtmlcxx pkg-config libglog --libs --cflags -I/usr/include/python2.6 -Wall -Wextra" But when I run python and I import it, I get: import pyhosters Traceback (most recent call last): File "", line 1, in File "./pyhosters.py", line 7, in import _pyhosters ImportError: ./_pyhosters.so: undefined symbol: _ZN7hosters11hostersLink7getLinkEi How can I solve that? Thanks.

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• Fun programming languages

  - by Jason Baker

  What are some fun programming languages to learn and work with? I'm asking this for absolutely no practical purpose other than just to learn something new. So, what are some fun languages? I already know Python and C# so those don't count (although Python would probably be the first language I'd recommend). I've spent some time with Ruby, but I don't really see anything that's a whole lot different from Python. (and no, I'm not going to learn Intercal or Brainf*ck before you mention it)

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• Scala Tuple Deconstruction

  - by dbyrne

  I am new to Scala, and ran across a small hiccup that has been annoying me. Initializing two vars in parallel works great: var (x,y) = (1,2) However I can't find a way to assign new values in parallel: (x,y) = (x+y,y-x) //invalid syntax I end up writing something like this: val xtmp = x+y; y = x-y; x = xtmp I realize writing functional code is one way of avoiding this, but there are certain situations where vars just make more sense. I have two questions: 1) Is there a better way of doing this? Am I missing something? 2) What is the reason for not allowing true parallel assignment?

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• Symbol not found: _curl_easy_cleanup

  - by Bharadwaj

  I am working on porting a python application to Mac OS X. The application makes use of pycurl and PyCDF. When I run my code, I get this error : > File > "/Library/Python/2.5/site-packages/pycdf/pycdfext.py", > line 5, in <module> > import _pycdfext ImportError: dlopen(/Library/Python/2.5/site-packages/pycdf/_pycdfext.so, > 2): Symbol not found: > _curl_easy_cleanup Referenced from: /Library/Python/2.5/site-packages/pycdf/_pycdfext.so > Expected in: dynamic lookup I tried installing different versions of curl, pycurl with different configs of libcurl. Still stuck Platform : 10.5.8 Curl : 7.19.4 [also tried 7.20.1] Pycurl : 7.19.0 How do I fix this error?

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• System Error when running PyQt4's loadUi()

  - by user633804

  Hello, I'm pretty new to Qt, Python and their combinations. I'm currently writing a QGIS plugin in python (I used QtCreator 2.1 (Qt Designer 4.7) to generate a .ui-file and am now trying to use it for a Quantum GIS plugin that's written in Python 2.5 (and running in the Quantum GIS Python 2.5 console)). I am running into trouble when loading the ui-file dynamically when the program runs the loadUi() function. What throws me off is that the error occurs outside my script. Does that mean, I'm passing something wrong into it? Where does the error come in? Any hints on what could be wrong? code_dir = os.path.dirname(os.path.abspath(__file__)) self.ui = loadUi(os.path.join(code_dir, "Ui_myfile.ui"), self) This is the Error Code I am getting (minus the first paragraph): File "C:/Dokumente und Einstellungen/name.name/.qgis/python/plugins\myfile\myfile_gui.py", line 42, in __ init __ self.ui = loadUi(os.path.join(code_dir, "Ui_myfile.ui"), self) File "C:\PROGRA~1\QUANTU~1\apps\Python25\lib\site-packages\PyQt4\uic__init__.py", line 112, in loadUi return DynamicUILoader().loadUi(uifile, baseinstance) File "C:\PROGRA~1\QUANTU~1\apps\Python25\lib\site-packages\PyQt4\uic\Loader\loader.py", line 21, in loadUi return self.parse(filename) File "C:\PROGRA~1\QUANTU~1\apps\Python25\lib\site-packages\PyQt4\uic\uiparser.py", line 768, in parse actor(elem) File "C:\PROGRA~1\QUANTU~1\apps\Python25\lib\site-packages\PyQt4\uic\uiparser.py", line 616, in createUserInterface self.traverseWidgetTree(elem) File "C:\PROGRA~1\QUANTU~1\apps\Python25\lib\site-packages\PyQt4\uic\uiparser.py", line 594, in traverseWidgetTree handler(self, child) File "C:\PROGRA~1\QUANTU~1\apps\Python25\lib\site-packages\PyQt4\uic\uiparser.py", line 233, in createWidget topwidget.setCentralWidget(widget) SystemError: error return without exception set

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• How do I make a project in Django? Beginner

  - by ggfan

  Okay I just started with Django and it's totally different from PHP. I installed Python 2.6 and Django. Both are located in my C drive. C: Django build django docs Python26 I am doing the django site tutorial and when they say to write django-admin.py startproject mysite from my Python command line, I keep getting: Syntax error: invalid syntax >>>django-admin.py startproject mysite FILE "<stdin>", line 1 django-admin.py startproject mysite ^ My django-admin.py is in the django/bin folder. I installed Python via python setup.py. Am I suppose to use my window's CP? When I do that, I get window's can't open a .py file. I thought I was just creating a folder? How do I create a project with django? Thanks :)

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• error calling c# com interop dll

  - by aF

  Hello, I have a python project that calls a c++ dll that calls a c# dll. I wanted all to run without installing visual studio 2008. I allready made the c++ part by installing Visual C++ 2008 SP1 Redistributable Package (x86) and I also installed .net framework 3.5. But now, when I call a function from c++ dll (and this one calls its correspondent in c#), it gives me this error: Traceback (most recent call last): File "C:\Users\Public\SoundLog\Code\Código Python\SoundLog\SoundLog.py", line 821, in OnStart Auxiliar.DataCollection.start(self) File "C:\Users\Public\SoundLog\Code\Código Python\SoundLog\Auxiliar\DataCollection.py", line 68, in start SoundLogDLL.run() File "C:\Users\Public\SoundLog\Code\Código Python\SoundLog\Auxiliar\SoundLogDLL.py", line 61, in run return apiRun() WindowsError: exception code 0xe0434f4d This works where I've installed full VS2008 pro version. What am I missing and what can I do to solve this?

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• a good Java guide

  - by Lo'oris

  Do you know a good guide for Java, such as "dive into python" for python? If I searched google I expect I would find tons of random guides, but trying them all until I found a good one could take ages... that's why I am asking: do you already know one in particular? one you KNOW is good? I already know C, PHP and a bit of Python, if that matters.

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• Receiving UDP on different Android phones gives different results

  - by user1868982

  I am willing to create a server and client program on my android mobile devices. The devices communicate with each other on the same wifi network, therefore, some simple scanning mechanism must be implemented - The client phones search for a server phone through some kind of broadcast. What I did: My protocol - the client phone broadcasts a message port p on the wifi, the server listens on port p. when the server gets the broadcast message it sends a message back, therefore discovering itself to the client. My code - I have opened a broadcast socket on my app, it sends a broadcast message. Meanwhile there is a python script on my PC that listens and replies - I use python so that my testing will be easier - Wireshark on the PC and I can see everything. What happens: When I use one of my Galaxy S phones - it works and I get a response. When I use the other Galaxy S phone - it doesn't work. Now this is what I know: The phone that works actually has Nexus ROM on it Ver. 4.1.1 The phone that doesn't work has 2.3.3 regular galaxy ROM The python code says it receives both of the broadcasts sent from both phones, and replies to both of them without raising any exception. So far I was thought the problem may be 1. the older version'd phone. 2. the windows firewall 3. the router firewall So I have opened Wireshark, and Indeed I saw that both phones are sending their broadcasts - it was logged on Wireshark. But the python script only responded to the first one. So this is why 1 & 3 are irrelevant - if the router firewall was blocking my UDP I would have still seen the python server response, same with the older versioned phone. To get rid of 2 i just disabled the windows firewall - still same problem. Does anyone has a clue to why this effect might happen? Thanks!

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• GAE/J datastore backup

  - by jb

  What is the easiest way to do a GAE/J datastore backup? It looks like there is python bulkloader.py tool to do backup for Python apps, but what should I do to backup Java app? Is there any way to use python tool?

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• select GUI on windows (wxPy vs pyQt)

  - by Golovko

  Hello! We are plan to create an application for monitoring and configuring our service (which is running on remote server). After long time discuss, we decide for python as pl for our app, because we love and know python (better, than english, really). but we don't know, what GUI toolkit preffered for our aims. We need fast (for development and running) app, which users are admins, mainteners and account managers. There is two GUI toolkit for python, which we know: wxPython and pyQT. Anybody have arguments pro et contra candidat? And maybe peoples know commercial applications, running in this products (only python version of toolkits)? Links are desirable. Thanks, and excuse my english.

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• What's a good way to organize a large collection of personal scripts using git?

  - by spooky note

  I have a large collection of my personal scripts that I would like to start versioning using Git. I've previously organized my code as follows: ~/code/python/projects/ (for large stuff, each project contained in an individual folder) ~/code/python/scripts/ (single file scripts all contained in this directory) ~/code/python/sandbox/ (my testing area) ~/code/python/docs/ (downloaded documentation) ~/code/java/... (as above) Now i'm going to start versioning my code using git, so that I can have history and backup all my code to a remote server. I know if I were using SVN I would just keep my entire "~/code/" directory in a large repository, but I understand this is not a good way to do things with Git. Most info I've seen online suggests keeping all my project folders in a single place (as in, no separate directories for python or java) with each project containing it's own git repository, and simply having a "snippets" directory containing all single-file scripts/experiments that can be converted into projects at a later date. But I'm not sure how I feel about consolidating all of my code directories into one area. Is there a good way to keep my separate code directories intact, or is it not worth the effort? Maybe I'm just attached to the separate code directories because I've never known anything else... Also (as a side note), I'd like to quickly be able to see a chronological history of all my projects and scripts. So I can see which projects I created most recently. I used to do this by keeping a number at the beginning of all my projects, 002project, 003project. Is there automatic or easy way to do this in git without having to add a number to all of the project names? I'm open to any practical or philosophical code organizing advice you have. Thanks!!!

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• What type of programs are C/C++ used for now?

  - by Ryan Detzel

  I started off with C in school, went to Java and now I primarily use the P's(Php, Perl, Python) so my exposure to the lower level languages have all but disappeared. I would like to get back into it but I can never justify using C over Perl or Python. What real-world apps are being built with these languages? Any suggestions if I want to dive back in, what can I do with C/C++ that I can't easily do with Perl/Python?

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• Juju Openstack bundle: Can't launch an instance

  - by user281985

  Deployed bundle:~makyo/openstack/2/openstack, on top of 7 physical boxes and 3 virtual ones. After changing vip_iface strings to point to right devices, e.g., br0 instead of eth0, and defining "/mnt/loopback|30G", in Cinder's block-device string, am able to navigate through openstack dashboard, error free. Following http://docs.openstack.org/grizzly/openstack-compute/install/apt/content/running-an-instance.html instructions, attempted to launch cirros 0.3.1 image; however, novalist shows the instance in error state. ubuntu@node7:~$ nova --debug boot --flavor 1 --image 28bed1bc-bc1c-4533-beee-8e0428ad40dd --key_name key2 --security_group default cirros REQ: curl -i http://keyStone.IP:5000/v2.0/tokens -X POST -H "Content-Type: application/json" -H "Accept: application/json" -H "User-Agent: python-novaclient" -d '{"auth": {"tenantName": "admin", "passwordCredentials": {"username": "admin", "password": "openstack"}}}' INFO (connectionpool:191) Starting new HTTP connection (1): keyStone.IP DEBUG (connectionpool:283) "POST /v2.0/tokens HTTP/1.1" 200 None RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:02 GMT', 'transfer-encoding': 'chunked', 'vary': 'X-Auth-Token', 'content-type': 'application/json'} RESP BODY: {"access": {"token": {"expires": "2014-06-11T00:01:02Z", "id": "3eefa1837d984426a633fe09259a1534", "tenant": {"description": "Created by Juju", "enabled": true, "id": "08cff06d13b74492b780d9ceed699239", "name": "admin"}}, "serviceCatalog": [{"endpoints": [{"adminURL": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239", "publicURL": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239"}], "endpoints_links": [], "type": "compute", "name": "nova"}, {"endpoints": [{"adminURL": "http://nova.cloud.controller:9696", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:9696", "publicURL": "http://nova.cloud.controller:9696"}], "endpoints_links": [], "type": "network", "name": "quantum"}, {"endpoints": [{"adminURL": "http://nova.cloud.controller:3333", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:3333", "publicURL": "http://nova.cloud.controller:3333"}], "endpoints_links": [], "type": "s3", "name": "s3"}, {"endpoints": [{"adminURL": "http://i.p.s.36:9292", "region": "RegionOne", "internalURL": "http://i.p.s.36:9292", "publicURL": "http://i.p.s.36:9292"}], "endpoints_links": [], "type": "image", "name": "glance"}, {"endpoints": [{"adminURL": "http://i.p.s.39:8776/v1/08cff06d13b74492b780d9ceed699239", "region": "RegionOne", "internalURL": "http://i.p.s.39:8776/v1/08cff06d13b74492b780d9ceed699239", "publicURL": "http://i.p.s.39:8776/v1/08cff06d13b74492b780d9ceed699239"}], "endpoints_links": [], "type": "volume", "name": "cinder"}, {"endpoints": [{"adminURL": "http://nova.cloud.controller:8773/services/Cloud", "region": "RegionOne", "internalURL": "http://nova.cloud.controller:8773/services/Cloud", "publicURL": "http://nova.cloud.controller:8773/services/Cloud"}], "endpoints_links": [], "type": "ec2", "name": "ec2"}, {"endpoints": [{"adminURL": "http://keyStone.IP:35357/v2.0", "region": "RegionOne", "internalURL": "http://keyStone.IP:5000/v2.0", "publicURL": "http://i.p.s.44:5000/v2.0"}], "endpoints_links": [], "type": "identity", "name": "keystone"}], "user": {"username": "admin", "roles_links": [], "id": "b3730a52a32e40f0a9500440d1ef1c7d", "roles": [{"id": "e020001eb9a049f4a16540238ab158aa", "name": "Admin"}, {"id": "b84fbff4d5554d53bbbffdaad66b56cb", "name": "KeystoneServiceAdmin"}, {"id": "129c8b49d42b4f0796109aaef2069aa9", "name": "KeystoneAdmin"}], "name": "admin"}}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd HTTP/1.1" 200 719 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:03 GMT', 'x-compute-request-id': 'req-7f3459f8-d3d5-47f1-97a3-8407a4419a69', 'content-type': 'application/json', 'content-length': '719'} RESP BODY: {"image": {"status": "ACTIVE", "updated": "2014-06-09T22:17:54Z", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "bookmark"}, {"href": "http://External.Public.Port:9292/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "type": "application/vnd.openstack.image", "rel": "alternate"}], "id": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "OS-EXT-IMG-SIZE:size": 13147648, "name": "Cirros 0.3.1", "created": "2014-06-09T22:17:54Z", "minDisk": 0, "progress": 100, "minRam": 0, "metadata": {}}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 HTTP/1.1" 200 418 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:04 GMT', 'x-compute-request-id': 'req-2c153110-6969-4f3a-b51c-8f1a6ce75bee', 'content-type': 'application/json', 'content-length': '418'} RESP BODY: {"flavor": {"name": "m1.tiny", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "bookmark"}], "ram": 512, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "1"}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers -X POST -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Content-Type: application/json" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" -d '{"server": {"name": "cirros", "imageRef": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "key_name": "key2", "flavorRef": "1", "max_count": 1, "min_count": 1, "security_groups": [{"name": "default"}]}}' INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "POST /v1.1/08cff06d13b74492b780d9ceed699239/servers HTTP/1.1" 202 436 RESP: [202] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-41e53086-6454-4efb-bb35-a30dc2c780be', 'content-type': 'application/json', 'location': 'http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43', 'content-length': '436'} RESP BODY: {"server": {"security_groups": [{"name": "default"}], "OS-DCF:diskConfig": "MANUAL", "id": "2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "bookmark"}], "adminPass": "oFRbvRqif2C8"}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43 -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43 HTTP/1.1" 200 1349 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-d91d0858-7030-469d-8e55-40e05e4d00fd', 'content-type': 'application/json', 'content-length': '1349'} RESP BODY: {"server": {"status": "BUILD", "updated": "2014-06-10T00:01:05Z", "hostId": "", "OS-EXT-SRV-ATTR:host": null, "addresses": {}, "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/servers/2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "rel": "bookmark"}], "key_name": "key2", "image": {"id": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "links": [{"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "bookmark"}]}, "OS-EXT-STS:task_state": "scheduling", "OS-EXT-STS:vm_state": "building", "OS-EXT-SRV-ATTR:instance_name": "instance-00000004", "OS-EXT-SRV-ATTR:hypervisor_hostname": null, "flavor": {"id": "1", "links": [{"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "bookmark"}]}, "id": "2eb5e3ad-3044-41c1-bbb7-10f398f83e43", "security_groups": [{"name": "default"}], "OS-EXT-AZ:availability_zone": "nova", "user_id": "b3730a52a32e40f0a9500440d1ef1c7d", "name": "cirros", "created": "2014-06-10T00:01:04Z", "tenant_id": "08cff06d13b74492b780d9ceed699239", "OS-DCF:diskConfig": "MANUAL", "accessIPv4": "", "accessIPv6": "", "progress": 0, "OS-EXT-STS:power_state": 0, "config_drive": "", "metadata": {}}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/flavors/1 HTTP/1.1" 200 418 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-896c0120-1102-4408-9e09-cd628f2dd699', 'content-type': 'application/json', 'content-length': '418'} RESP BODY: {"flavor": {"name": "m1.tiny", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/flavors/1", "rel": "bookmark"}], "ram": 512, "OS-FLV-DISABLED:disabled": false, "vcpus": 1, "swap": "", "os-flavor-access:is_public": true, "rxtx_factor": 1.0, "OS-FLV-EXT-DATA:ephemeral": 0, "disk": 0, "id": "1"}} REQ: curl -i http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd -X GET -H "X-Auth-Project-Id: admin" -H "User-Agent: python-novaclient" -H "Accept: application/json" -H "X-Auth-Token: 3eefa1837d984426a633fe09259a1534" INFO (connectionpool:191) Starting new HTTP connection (1): nova.cloud.controller DEBUG (connectionpool:283) "GET /v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd HTTP/1.1" 200 719 RESP: [200] {'date': 'Tue, 10 Jun 2014 00:01:05 GMT', 'x-compute-request-id': 'req-454e9651-c247-4d31-8049-6b254de050ae', 'content-type': 'application/json', 'content-length': '719'} RESP BODY: {"image": {"status": "ACTIVE", "updated": "2014-06-09T22:17:54Z", "links": [{"href": "http://nova.cloud.controller:8774/v1.1/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "self"}, {"href": "http://nova.cloud.controller:8774/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "rel": "bookmark"}, {"href": "http://External.Public.Port:9292/08cff06d13b74492b780d9ceed699239/images/28bed1bc-bc1c-4533-beee-8e0428ad40dd", "type": "application/vnd.openstack.image", "rel": "alternate"}], "id": "28bed1bc-bc1c-4533-beee-8e0428ad40dd", "OS-EXT-IMG-SIZE:size": 13147648, "name": "Cirros 0.3.1", "created": "2014-06-09T22:17:54Z", "minDisk": 0, "progress": 100, "minRam": 0, "metadata": {}}} +-------------------------------------+--------------------------------------+ | Property | Value | +-------------------------------------+--------------------------------------+ | OS-EXT-STS:task_state | scheduling | | image | Cirros 0.3.1 | | OS-EXT-STS:vm_state | building | | OS-EXT-SRV-ATTR:instance_name | instance-00000004 | | flavor | m1.tiny | | id | 2eb5e3ad-3044-41c1-bbb7-10f398f83e43 | | security_groups | [{u'name': u'default'}] | | user_id | b3730a52a32e40f0a9500440d1ef1c7d | | OS-DCF:diskConfig | MANUAL | | accessIPv4 | | | accessIPv6 | | | progress | 0 | | OS-EXT-STS:power_state | 0 | | OS-EXT-AZ:availability_zone | nova | | config_drive | | | status | BUILD | | updated | 2014-06-10T00:01:05Z | | hostId | | | OS-EXT-SRV-ATTR:host | None | | key_name | key2 | | OS-EXT-SRV-ATTR:hypervisor_hostname | None | | name | cirros | | adminPass | oFRbvRqif2C8 | | tenant_id | 08cff06d13b74492b780d9ceed699239 | | created | 2014-06-10T00:01:04Z | | metadata | {} | +-------------------------------------+--------------------------------------+ ubuntu@node7:~$ ubuntu@node7:~$ nova list +--------------------------------------+--------+--------+----------+ | ID | Name | Status | Networks | +--------------------------------------+--------+--------+----------+ | 2eb5e3ad-3044-41c1-bbb7-10f398f83e43 | cirros | ERROR | | +--------------------------------------+--------+--------+----------+ ubuntu@node7:~$ var/log/nova/nova-compute.log shows the following error: ... 2014-06-10 00:01:06.048 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Attempting claim: memory 512 MB, disk 0 GB, VCPUs 1 2014-06-10 00:01:06.049 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Total Memory: 3885 MB, used: 512 MB 2014-06-10 00:01:06.049 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Memory limit: 5827 MB, free: 5315 MB 2014-06-10 00:01:06.049 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Total Disk: 146 GB, used: 0 GB 2014-06-10 00:01:06.050 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Disk limit not specified, defaulting to unlimited 2014-06-10 00:01:06.050 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Total CPU: 2 VCPUs, used: 0 VCPUs 2014-06-10 00:01:06.050 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] CPU limit not specified, defaulting to unlimited 2014-06-10 00:01:06.051 AUDIT nova.compute.claims [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Claim successful 2014-06-10 00:01:06.963 WARNING nova.network.quantumv2.api [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] No network configured! 2014-06-10 00:01:08.347 ERROR nova.compute.manager [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Instance failed to spawn 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Traceback (most recent call last): 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1118, in _spawn 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] self._legacy_nw_info(network_info), 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 703, in _legacy_nw_info 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] network_info = network_info.legacy() 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] AttributeError: 'list' object has no attribute 'legacy' 2014-06-10 00:01:08.347 32223 TRACE nova.compute.manager [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] 2014-06-10 00:01:08.919 AUDIT nova.compute.manager [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Terminating instance 2014-06-10 00:01:09.712 32223 ERROR nova.virt.libvirt.driver [-] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] During wait destroy, instance disappeared. 2014-06-10 00:01:09.718 INFO nova.virt.libvirt.firewall [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Attempted to unfilter instance which is not filtered 2014-06-10 00:01:09.719 INFO nova.virt.libvirt.driver [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Deleting instance files /var/lib/nova/instances/2eb5e3ad-3044-41c1-bbb7-10f398f83e43 2014-06-10 00:01:10.044 ERROR nova.compute.manager [req-41e53086-6454-4efb-bb35-a30dc2c780be b3730a52a32e40f0a9500440d1ef1c7d 08cff06d13b74492b780d9ceed699239] [instance: 2eb5e3ad-3044-41c1-bbb7-10f398f83e43] Error: ['Traceback (most recent call last):\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 864, in _run_instance\n set_access_ip=set_access_ip)\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1123, in _spawn\n LOG.exception(_(\'Instance failed to spawn\'), instance=instance)\n', ' File "/usr/lib/python2.7/contextlib.py", line 24, in __exit__\n self.gen.next()\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 1118, in _spawn\n self._legacy_nw_info(network_info),\n', ' File "/usr/lib/python2.7/dist-packages/nova/compute/manager.py", line 703, in _legacy_nw_info\n network_info = network_info.legacy()\n', "AttributeError: 'list' object has no attribute 'legacy'\n"] 2014-06-10 00:01:40.951 32223 AUDIT nova.compute.resource_tracker [-] Auditing locally available compute resources 2014-06-10 00:01:41.072 32223 AUDIT nova.compute.resource_tracker [-] Free ram (MB): 2861 2014-06-10 00:01:41.072 32223 AUDIT nova.compute.resource_tracker [-] Free disk (GB): 146 2014-06-10 00:01:41.073 32223 AUDIT nova.compute.resource_tracker [-] Free VCPUS: 1 2014-06-10 00:01:41.262 32223 INFO nova.compute.resource_tracker [-] Compute_service record updated for node5:node5.maas ... Can't seem to find any entries in quantum.conf related to "legacy". Any help would be appreciated. Cheers,

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• C#/.NET Little Wonders: The Concurrent Collections (1 of 3)

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  In the next few weeks, we will discuss the concurrent collections and how they have changed the face of concurrent programming. This week’s post will begin with a general introduction and discuss the ConcurrentStack<T> and ConcurrentQueue<T>.  Then in the following post we’ll discuss the ConcurrentDictionary<T> and ConcurrentBag<T>.  Finally, we shall close on the third post with a discussion of the BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. A brief history of collections In the beginning was the .NET 1.0 Framework.  And out of this framework emerged the System.Collections namespace, and it was good.  It contained all the basic things a growing programming language needs like the ArrayList and Hashtable collections.  The main problem, of course, with these original collections is that they held items of type object which means you had to be disciplined enough to use them correctly or you could end up with runtime errors if you got an object of a type you weren't expecting. Then came .NET 2.0 and generics and our world changed forever!  With generics the C# language finally got an equivalent of the very powerful C++ templates.  As such, the System.Collections.Generic was born and we got type-safe versions of all are favorite collections.  The List<T> succeeded the ArrayList and the Dictionary<TKey,TValue> succeeded the Hashtable and so on.  The new versions of the library were not only safer because they checked types at compile-time, in many cases they were more performant as well.  So much so that it's Microsoft's recommendation that the System.Collections original collections only be used for backwards compatibility. So we as developers came to know and love the generic collections and took them into our hearts and embraced them.  The problem is, thread safety in both the original collections and the generic collections can be problematic, for very different reasons. Now, if you are only doing single-threaded development you may not care – after all, no locking is required.  Even if you do have multiple threads, if a collection is “load-once, read-many” you don’t need to do anything to protect that container from multi-threaded access, as illustrated below: 1: public static class OrderTypeTranslator 2: { 3: // because this dictionary is loaded once before it is ever accessed, we don't need to synchronize 4: // multi-threaded read access 5: private static readonly Dictionary<string, char> _translator = new Dictionary<string, char> 6: { 7: {"New", 'N'}, 8: {"Update", 'U'}, 9: {"Cancel", 'X'} 10: }; 11:  12: // the only public interface into the dictionary is for reading, so inherently thread-safe 13: public static char? Translate(string orderType) 14: { 15: char charValue; 16: if (_translator.TryGetValue(orderType, out charValue)) 17: { 18: return charValue; 19: } 20:  21: return null; 22: } 23: } Unfortunately, most of our computer science problems cannot get by with just single-threaded applications or with multi-threading in a load-once manner.  Looking at  today's trends, it's clear to see that computers are not so much getting faster because of faster processor speeds -- we've nearly reached the limits we can push through with today's technologies -- but more because we're adding more cores to the boxes.  With this new hardware paradigm, it is even more important to use multi-threaded applications to take full advantage of parallel processing to achieve higher application speeds. So let's look at how to use collections in a thread-safe manner. Using historical collections in a concurrent fashion The early .NET collections (System.Collections) had a Synchronized() static method that could be used to wrap the early collections to make them completely thread-safe.  This paradigm was dropped in the generic collections (System.Collections.Generic) because having a synchronized wrapper resulted in atomic locks for all operations, which could prove overkill in many multithreading situations.  Thus the paradigm shifted to having the user of the collection specify their own locking, usually with an external object: 1: public class OrderAggregator 2: { 3: private static readonly Dictionary<string, List<Order>> _orders = new Dictionary<string, List<Order>>(); 4: private static readonly _orderLock = new object(); 5:  6: public void Add(string accountNumber, Order newOrder) 7: { 8: List<Order> ordersForAccount; 9:  10: // a complex operation like this should all be protected 11: lock (_orderLock) 12: { 13: if (!_orders.TryGetValue(accountNumber, out ordersForAccount)) 14: { 15: _orders.Add(accountNumber, ordersForAccount = new List<Order>()); 16: } 17:  18: ordersForAccount.Add(newOrder); 19: } 20: } 21: } Notice how we’re performing several operations on the dictionary under one lock.  With the Synchronized() static methods of the early collections, you wouldn’t be able to specify this level of locking (a more macro-level).  So in the generic collections, it was decided that if a user needed synchronization, they could implement their own locking scheme instead so that they could provide synchronization as needed. The need for better concurrent access to collections Here’s the problem: it’s relatively easy to write a collection that locks itself down completely for access, but anything more complex than that can be difficult and error-prone to write, and much less to make it perform efficiently!  For example, what if you have a Dictionary that has frequent reads but in-frequent updates?  Do you want to lock down the entire Dictionary for every access?  This would be overkill and would prevent concurrent reads.  In such cases you could use something like a ReaderWriterLockSlim which allows for multiple readers in a lock, and then once a writer grabs the lock it blocks all further readers until the writer is done (in a nutshell).  This is all very complex stuff to consider. Fortunately, this is where the Concurrent Collections come in.  The Parallel Computing Platform team at Microsoft went through great pains to determine how to make a set of concurrent collections that would have the best performance characteristics for general case multi-threaded use. Now, as in all things involving threading, you should always make sure you evaluate all your container options based on the particular usage scenario and the degree of parallelism you wish to acheive. This article should not be taken to understand that these collections are always supperior to the generic collections. Each fills a particular need for a particular situation. Understanding what each container is optimized for is key to the success of your application whether it be single-threaded or multi-threaded. General points to consider with the concurrent collections The MSDN points out that the concurrent collections all support the ICollection interface. However, since the collections are already synchronized, the IsSynchronized property always returns false, and SyncRoot always returns null.  Thus you should not attempt to use these properties for synchronization purposes. Note that since the concurrent collections also may have different operations than the traditional data structures you may be used to.  Now you may ask why they did this, but it was done out of necessity to keep operations safe and atomic.  For example, in order to do a Pop() on a stack you have to know the stack is non-empty, but between the time you check the stack’s IsEmpty property and then do the Pop() another thread may have come in and made the stack empty!  This is why some of the traditional operations have been changed to make them safe for concurrent use. In addition, some properties and methods in the concurrent collections achieve concurrency by creating a snapshot of the collection, which means that some operations that were traditionally O(1) may now be O(n) in the concurrent models.  I’ll try to point these out as we talk about each collection so you can be aware of any potential performance impacts.  Finally, all the concurrent containers are safe for enumeration even while being modified, but some of the containers support this in different ways (snapshot vs. dirty iteration).  Once again I’ll highlight how thread-safe enumeration works for each collection. ConcurrentStack<T>: The thread-safe LIFO container The ConcurrentStack<T> is the thread-safe counterpart to the System.Collections.Generic.Stack<T>, which as you may remember is your standard last-in-first-out container.  If you think of algorithms that favor stack usage (for example, depth-first searches of graphs and trees) then you can see how using a thread-safe stack would be of benefit. The ConcurrentStack<T> achieves thread-safe access by using System.Threading.Interlocked operations.  This means that the multi-threaded access to the stack requires no traditional locking and is very, very fast! For the most part, the ConcurrentStack<T> behaves like it’s Stack<T> counterpart with a few differences: Pop() was removed in favor of TryPop() Returns true if an item existed and was popped and false if empty. PushRange() and TryPopRange() were added Allows you to push multiple items and pop multiple items atomically. Count takes a snapshot of the stack and then counts the items. This means it is a O(n) operation, if you just want to check for an empty stack, call IsEmpty instead which is O(1). ToArray() and GetEnumerator() both also take snapshots. This means that iteration over a stack will give you a static view at the time of the call and will not reflect updates. Pushing on a ConcurrentStack<T> works just like you’d expect except for the aforementioned PushRange() method that was added to allow you to push a range of items concurrently. 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: // but you can also push multiple items in one atomic operation (no interleaves) 7: stack.PushRange(new [] { "Second", "Third", "Fourth" }); For looking at the top item of the stack (without removing it) the Peek() method has been removed in favor of a TryPeek().  This is because in order to do a peek the stack must be non-empty, but between the time you check for empty and the time you execute the peek the stack contents may have changed.  Thus the TryPeek() was created to be an atomic check for empty, and then peek if not empty: 1: // to look at top item of stack without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (stack.TryPeek(out item)) 5: { 6: Console.WriteLine("Top item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Stack was empty."); 11: } Finally, to remove items from the stack, we have the TryPop() for single, and TryPopRange() for multiple items.  Just like the TryPeek(), these operations replace Pop() since we need to ensure atomically that the stack is non-empty before we pop from it: 1: // to remove items, use TryPop or TryPopRange to get multiple items atomically (no interleaves) 2: if (stack.TryPop(out item)) 3: { 4: Console.WriteLine("Popped " + item); 5: } 6:  7: // TryPopRange will only pop up to the number of spaces in the array, the actual number popped is returned. 8: var poppedItems = new string[2]; 9: int numPopped = stack.TryPopRange(poppedItems); 10:  11: foreach (var theItem in poppedItems.Take(numPopped)) 12: { 13: Console.WriteLine("Popped " + theItem); 14: } Finally, note that as stated before, GetEnumerator() and ToArray() gets a snapshot of the data at the time of the call.  That means if you are enumerating the stack you will get a snapshot of the stack at the time of the call.  This is illustrated below: 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: var results = stack.GetEnumerator(); 7:  8: // but you can also push multiple items in one atomic operation (no interleaves) 9: stack.PushRange(new [] { "Second", "Third", "Fourth" }); 10:  11: while(results.MoveNext()) 12: { 13: Console.WriteLine("Stack only has: " + results.Current); 14: } The only item that will be printed out in the above code is "First" because the snapshot was taken before the other items were added. This may sound like an issue, but it’s really for safety and is more correct.  You don’t want to enumerate a stack and have half a view of the stack before an update and half a view of the stack after an update, after all.  In addition, note that this is still thread-safe, whereas iterating through a non-concurrent collection while updating it in the old collections would cause an exception. ConcurrentQueue<T>: The thread-safe FIFO container The ConcurrentQueue<T> is the thread-safe counterpart of the System.Collections.Generic.Queue<T> class.  The concurrent queue uses an underlying list of small arrays and lock-free System.Threading.Interlocked operations on the head and tail arrays.  Once again, this allows us to do thread-safe operations without the need for heavy locks! The ConcurrentQueue<T> (like the ConcurrentStack<T>) has some departures from the non-concurrent counterpart.  Most notably: Dequeue() was removed in favor of TryDequeue(). Returns true if an item existed and was dequeued and false if empty. Count does not take a snapshot It subtracts the head and tail index to get the count.  This results overall in a O(1) complexity which is quite good.  It’s still recommended, however, that for empty checks you call IsEmpty instead of comparing Count to zero. ToArray() and GetEnumerator() both take snapshots. This means that iteration over a queue will give you a static view at the time of the call and will not reflect updates. The Enqueue() method on the ConcurrentQueue<T> works much the same as the generic Queue<T>: 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5: queue.Enqueue("Second"); 6: queue.Enqueue("Third"); For front item access, the TryPeek() method must be used to attempt to see the first item if the queue.  There is no Peek() method since, as you’ll remember, we can only peek on a non-empty queue, so we must have an atomic TryPeek() that checks for empty and then returns the first item if the queue is non-empty. 1: // to look at first item in queue without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (queue.TryPeek(out item)) 5: { 6: Console.WriteLine("First item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Queue was empty."); 11: } Then, to remove items you use TryDequeue().  Once again this is for the same reason we have TryPeek() and not Peek(): 1: // to remove items, use TryDequeue. If queue is empty returns false. 2: if (queue.TryDequeue(out item)) 3: { 4: Console.WriteLine("Dequeued first item " + item); 5: } Just like the concurrent stack, the ConcurrentQueue<T> takes a snapshot when you call ToArray() or GetEnumerator() which means that subsequent updates to the queue will not be seen when you iterate over the results.  Thus once again the code below will only show the first item, since the other items were added after the snapshot. 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5:  6: var iterator = queue.GetEnumerator(); 7:  8: queue.Enqueue("Second"); 9: queue.Enqueue("Third"); 10:  11: // only shows First 12: while (iterator.MoveNext()) 13: { 14: Console.WriteLine("Dequeued item " + iterator.Current); 15: } Using collections concurrently You’ll notice in the examples above I stuck to using single-threaded examples so as to make them deterministic and the results obvious.  Of course, if we used these collections in a truly multi-threaded way the results would be less deterministic, but would still be thread-safe and with no locking on your part required! For example, say you have an order processor that takes an IEnumerable<Order> and handles each other in a multi-threaded fashion, then groups the responses together in a concurrent collection for aggregation.  This can be done easily with the TPL’s Parallel.ForEach(): 1: public static IEnumerable<OrderResult> ProcessOrders(IEnumerable<Order> orderList) 2: { 3: var proxy = new OrderProxy(); 4: var results = new ConcurrentQueue<OrderResult>(); 5:  6: // notice that we can process all these in parallel and put the results 7: // into our concurrent collection without needing any external locking! 8: Parallel.ForEach(orderList, 9: order => 10: { 11: var result = proxy.PlaceOrder(order); 12:  13: results.Enqueue(result); 14: }); 15:  16: return results; 17: } Summary Obviously, if you do not need multi-threaded safety, you don’t need to use these collections, but when you do need multi-threaded collections these are just the ticket! The plethora of features (I always think of the movie The Three Amigos when I say plethora) built into these containers and the amazing way they acheive thread-safe access in an efficient manner is wonderful to behold. Stay tuned next week where we’ll continue our discussion with the ConcurrentBag<T> and the ConcurrentDictionary<TKey,TValue>. For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here.   Tweet Technorati Tags: C#,.NET,Concurrent Collections,Collections,Multi-Threading,Little Wonders,BlackRabbitCoder,James Michael Hare

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• How to delete/edit files from readonly filesystem

  - by Santosh Linkha

  I am having problem with my memory device (actually a memory card that act external memory device like pendrive). experimentx@workmateX:/var/www/zendtest$ sudo rm /media/A88F-8788/python-2.7.1-docs-html.zip rm: cannot remove `/media/A88F-8788/python-2.7.1-docs-html.zip': Read-only file system I tried to change the file permission of the system but that doesn't work experimentx@workmateX:/var/www/zendtest$ sudo chmod 0777 /media/A88F-8788/python-2.7.1-docs-html.zip chmod: changing permissions of `/media/A88F-8788/python-2.7.1-docs-html.zip': Read-only file system But it perfectly works on windows. UPDATE On opening the drive and running command sudo mount -o remount,rw /media/A88F-8788 /var/log/syslog: Mar 23 15:29:48 workmateX kernel: [18042.257407] fat_get_cluster: 11 callbacks suppressed Mar 23 15:29:48 workmateX kernel: [18042.257414] FAT: Filesystem error (dev sdb1) Mar 23 15:29:48 workmateX kernel: [18042.257418] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:29:48 workmateX kernel: [18042.257425] FAT: Filesystem has been set read-only Mar 23 15:29:48 workmateX kernel: [18042.258187] FAT: Filesystem error (dev sdb1) Mar 23 15:29:48 workmateX kernel: [18042.258194] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.333787] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.333795] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.335949] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.335957] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.354903] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.354911] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.357213] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.357221] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.359547] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.359555] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.361929] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.361936] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.377416] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.377424] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.379384] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.379392] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.381898] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.381906] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:35 workmateX kernel: [18149.383764] FAT: Filesystem error (dev sdb1) Mar 23 15:31:35 workmateX kernel: [18149.383772] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.569747] fat_get_cluster: 11 callbacks suppressed Mar 23 15:31:40 workmateX kernel: [18154.569754] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.569758] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.569765] FAT: Filesystem has been set read-only Mar 23 15:31:40 workmateX kernel: [18154.572022] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.572029] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.582933] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.582941] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.585921] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.585929] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.587819] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.587827] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.597547] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.597555] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.599503] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.599511] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.602896] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.602905] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.615338] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.615346] fat_get_cluster: invalid cluster chain (i_pos 0) Mar 23 15:31:40 workmateX kernel: [18154.618574] FAT: Filesystem error (dev sdb1) Mar 23 15:31:40 workmateX kernel: [18154.618581] fat_get_cluster: invalid cluster chain (i_pos 0) var/log/message: Mar 23 15:29:48 workmateX kernel: [18042.257407] fat_get_cluster: 11 callbacks suppressed Mar 23 15:31:40 workmateX kernel: [18154.569747] fat_get_cluster: 11 callbacks suppressed

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• mailman web UI on localhost with apache2

  - by Thufir

  I'm interested only in running mailman on localhost and would like access to the web interface, but am getting 404: root@dur:~# root@dur:~# ln -s /etc/mailman/apache.conf /etc/apache2/sites-enabled/mailman -v `/etc/apache2/sites-enabled/mailman' -> `/etc/mailman/apache.conf' root@dur:~# root@dur:~# service apache2 restart * Restarting web server apache2 ... waiting . [ OK ] root@dur:~# root@dur:~# curl http://localhost/mailman/admin/ <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> <html><head> <title>404 Not Found</title> </head><body> <h1>Not Found</h1> <p>The requested URL /mailman/admin/ was not found on this server.</p> <hr> <address>Apache/2.2.22 (Ubuntu) Server at localhost Port 80</address> </body></html> root@dur:~# root@dur:~# tail /var/log/apache2/error.log [Mon Aug 27 13:08:02 2012] [error] [client 127.0.0.1] File does not exist: /var/www/mailman [Mon Aug 27 13:10:16 2012] [error] [client 127.0.0.1] File does not exist: /var/www/mailman [Mon Aug 27 13:29:27 2012] [notice] caught SIGTERM, shutting down [Mon Aug 27 13:29:27 2012] [error] python_init: Python version mismatch, expected '2.7.2+', found '2.7.3'. [Mon Aug 27 13:29:27 2012] [error] python_init: Python executable found '/usr/bin/python'. [Mon Aug 27 13:29:27 2012] [error] python_init: Python path being used '/usr/lib/python2.7/:/usr/lib/python2.7/plat-linux2:/usr/lib/python2.7/lib-tk:/usr/lib/python2.7/lib-old:/usr/lib/python2.7/lib-dynload'. [Mon Aug 27 13:29:27 2012] [notice] mod_python: Creating 8 session mutexes based on 6 max processes and 25 max threads. [Mon Aug 27 13:29:27 2012] [notice] mod_python: using mutex_directory /tmp [Mon Aug 27 13:29:28 2012] [notice] Apache/2.2.22 (Ubuntu) mod_python/3.3.1 Python/2.7.3 mod_ruby/1.2.6 Ruby/1.8.7(2011-06-30) configured -- resuming normal operations [Mon Aug 27 13:29:58 2012] [error] [client 127.0.0.1] File does not exist: /var/www/mailman root@dur:~# Although I did have to tinker a bit with mailmain to get that recognized. While I don't need to setup web access using MM list passwords, I would like to setup web admin to add/remove mailing lists. How do I configure apache or mailman so that I can navigate to http://localhost/mailman/admin/? As per installing mailman, I setup aliases as so: root@dur:~# root@dur:~# cat /etc/aliases usenet: root ## mailman mailing list mailman: "|/var/lib/mailman/mail/mailman post mailman" mailman-admin: "|/var/lib/mailman/mail/mailman admin mailman" mailman-bounces: "|/var/lib/mailman/mail/mailman bounces mailman" mailman-confirm: "|/var/lib/mailman/mail/mailman confirm mailman" mailman-join: "|/var/lib/mailman/mail/mailman join mailman" mailman-leave: "|/var/lib/mailman/mail/mailman leave mailman" mailman-owner: "|/var/lib/mailman/mail/mailman owner mailman" mailman-request: "|/var/lib/mailman/mail/mailman request mailman" mailman-subscribe: "|/var/lib/mailman/mail/mailman subscribe mailman" mailman-unsubscribe: "|/var/lib/mailman/mail/mailman unsubscribe mailman" root@dur:~# Perhaps these can be used somehow?

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• Diffusion de programmes PyQt4 autonomes sous Windows grâce à cx_Freeze, un article de Jean-Paul Vidal

  Bonjour, Comme j'en avais le besoin, j'ai réalisé 2 tutos, que je propose maintenant pour être transportés sur developpez (=> merci d'avance à dourouc05: dis-moi si tu as besoin du texte dokuwiki). Il s'agit de construire des programmes PyQt4 accompagnés de l'interpréteur Python et de toutes les bibliothèques nécessaires (dont PyQt4), afin qu'ils puissent fonctionner sur des PC sans aucune installation ni de Python ni de PyQt4: - Sous Windows (XP, Vista, 7) - Sous Linux (Ubuntu 10.10) Je pense que ce type de tuto...

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• SQL SERVER – CXPACKET – Parallelism – Usual Solution – Wait Type – Day 6 of 28

  - by pinaldave

  CXPACKET has to be most popular one of all wait stats. I have commonly seen this wait stat as one of the top 5 wait stats in most of the systems with more than one CPU. Books On-Line: Occurs when trying to synchronize the query processor exchange iterator. You may consider lowering the degree of parallelism if contention on this wait type becomes a problem. CXPACKET Explanation: When a parallel operation is created for SQL Query, there are multiple threads for a single query. Each query deals with a different set of the data (or rows). Due to some reasons, one or more of the threads lag behind, creating the CXPACKET Wait Stat. There is an organizer/coordinator thread (thread 0), which takes waits for all the threads to complete and gathers result together to present on the client’s side. The organizer thread has to wait for the all the threads to finish before it can move ahead. The Wait by this organizer thread for slow threads to complete is called CXPACKET wait. Note that not all the CXPACKET wait types are bad. You might experience a case when it totally makes sense. There might also be cases when this is unavoidable. If you remove this particular wait type for any query, then that query may run slower because the parallel operations are disabled for the query. Reducing CXPACKET wait: We cannot discuss about reducing the CXPACKET wait without talking about the server workload type. OLTP: On Pure OLTP system, where the transactions are smaller and queries are not long but very quick usually, set the “Maximum Degree of Parallelism” to 1 (one). This way it makes sure that the query never goes for parallelism and does not incur more engine overhead. EXEC sys.sp_configure N'cost threshold for parallelism', N'1' GO RECONFIGURE WITH OVERRIDE GO Data-warehousing / Reporting server: As queries will be running for long time, it is advised to set the “Maximum Degree of Parallelism” to 0 (zero). This way most of the queries will utilize the parallel processor, and long running queries get a boost in their performance due to multiple processors. EXEC sys.sp_configure N'cost threshold for parallelism', N'0' GO RECONFIGURE WITH OVERRIDE GO Mixed System (OLTP & OLAP): Here is the challenge. The right balance has to be found. I have taken a very simple approach. I set the “Maximum Degree of Parallelism” to 2, which means the query still uses parallelism but only on 2 CPUs. However, I keep the “Cost Threshold for Parallelism” very high. This way, not all the queries will qualify for parallelism but only the query with higher cost will go for parallelism. I have found this to work best for a system that has OLTP queries and also where the reporting server is set up. Here, I am setting ‘Cost Threshold for Parallelism’ to 25 values (which is just for illustration); you can choose any value, and you can find it out by experimenting with the system only. In the following script, I am setting the ‘Max Degree of Parallelism’ to 2, which indicates that the query that will have a higher cost (here, more than 25) will qualify for parallel query to run on 2 CPUs. This implies that regardless of the number of CPUs, the query will select any two CPUs to execute itself. EXEC sys.sp_configure N'cost threshold for parallelism', N'25' GO EXEC sys.sp_configure N'max degree of parallelism', N'2' GO RECONFIGURE WITH OVERRIDE GO Read all the post in the Wait Types and Queue series. Additionally a must read comment of Jonathan Kehayias. Note: The information presented here is from my experience and I no way claim it to be accurate. I suggest you all to read the online book for further clarification. All the discussion of Wait Stats over here is generic and it varies from system to system. It is recommended that you test this on the development server before implementing on the production server. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: DMV, Pinal Dave, PostADay, SQL, SQL Authority, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, T SQL, Technology

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• Garder les traductions avec cx_Freeze et PyQt4, un article de Jean-Paul Vidal

  Bonjour, Comme j'en avais le besoin, j'ai réalisé 2 tutos, que je propose maintenant pour être transportés sur developpez (=> merci d'avance à dourouc05: dis-moi si tu as besoin du texte dokuwiki). Il s'agit de construire des programmes PyQt4 accompagnés de l'interpréteur Python et de toutes les bibliothèques nécessaires (dont PyQt4), afin qu'ils puissent fonctionner sur des PC sans aucune installation ni de Python ni de PyQt4: - Sous Windows (XP, Vista, 7) - Sous Linux (Ubuntu 10.10) Je pense que ce type de tuto...

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