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• How to implement blocking request-reply using Java concurrency primitives?

  - by Uri

  My system consists of a "proxy" class that receives "request" packets, marshals them and sends them over the network to a server, which unmarshals them, processes, and returns some "response packet". My "submit" method on the proxy side should block until a reply is received to the request (packets have ids for identification and referencing purposes) or until a timeout is reached. If I was building this in early versions of Java, I would likely implement in my proxy a collection of "pending messages ids", where I would submit a message, and wait() on the corresponding id (with a timeout). When a reply was received, the handling thread would notify() on the corresponding id. Is there a better way to achieve this using an existing library class, perhaps in java.util.concurrency? If I went with the solution described above, what is the correct way to deal with the potential race condition where a reply arrives before wait() is invoked?

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• Delphi DateTimeFormat returning wrong year

  - by Leslie

  I have a form that allows users to enter a date of birth: ie: 4/16/40 Then when the user processes the form there's a function that checks it's length, adds leading zeros, parses the date and then uses FormatDateTime to just return the year of birth: strTemp := strPostedByDOB; If Length(strTemp) = 5 then strTemp = '0' + strTemp; if Length(strTemp) = 6 then begin strTemp := Copy(strTemp, 1 ,2) + '/' + copy(strTemp, 3, 2) + '/' + Copy(strTemp, 5, 2); strTemp := FormatDateTime('YYYY', StrToDate(strTemp)); end else strTemp := EmptyStr; using this code the strTemp is calculated as 2040 instead of 1940. Can anyone help me figure out how to make it show 1940 in strTemp? Do I have to change the form to accept a 4 digit year? Thanks, Leslie

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• Performing AJAX calls on the "new" controller

  - by shmichael

  In my rails app, I want to have a sortable list as part of an object creation. The best practice suggested Railscast adds the acts_as_list plugin and then initiates AJAX calls to update item position. However, AJAX calls won't work on an unsaved model, which is the situation with new. One solution would be to save the model immediately on new and redirect to edit. This would have a nice side effect of persisting any change so the user could resume work should he be interrupted. However, this solution adds the unwanted complexity of saving an invalid model, compromising rails' validation processes. Is there any better way to allow AJAX + validations without going into too much work?

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• python multiprocess update dictionary synchronously

  - by user1050325

  I am trying to update one common dictionary through multiple processes. Could you please help me find out what is the problem with this code? I get the following output: inside function {1: 1, 2: -1} comes here inside function {1: 0, 2: 2} comes here {1: 0, 2: -1} Thanks. from multiprocessing import Lock, Process, Manager l= Lock() def computeCopyNum(test,val): l.acquire() test[val]=val print "inside function" print test l.release() return a=dict({1: 0, 2: -1}) procs=list() for i in range(1,3): p = Process(target=computeCopyNum, args=(a,i)) procs.append(p) p.start() for p in procs: p.join() print "comes here" print a

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• Java Random Slowdowns on Mac OS cont'd

  - by javajustice

  I asked this question a few weeks ago, but I'm still having the problem and I have some new hints. The original question is here: http://stackoverflow.com/questions/1651887/java-random-slowdowns-on-mac-os Basically, I have a java application that splits a job into independent pieces and runs them in separate threads. The threads have no synchronization or shared memory items. The only resources they do share are data files on the hard disk, with each thread having an open file channel. Most of the time it runs very fast, but occasionally it will run very slow for no apparent reason. If I attach a CPU profiler to it, then it will start running quickly again. If I take a CPU snapshot, it says its spending most of its time in "self time" in a function that doesn't do anything except check a few (unshared unsynchronized) booleans. I don't know how this could be accurate because 1, it makes no sense, and 2, attaching the profiler seems to knock the threads out of whatever mode they're in and fix the problem. Also, regardless of whether it runs fast or slow, it always finishes and gives the same output, and it never dips in total cpu usage (in this case ~1500%), implying that the threads aren't getting blocked. I have tried different garbage collectors, different sizings the parts of the memory space, writing data output to non-raid drives, and putting all data output in threads separate the main worker threads. Does anyone have any idea what kind of problem this could be? Could it be the operating system (OS X 10.6.2) ? I have not been able to duplicate it on a windows machine, but I don't have one with a similar hardware configuration.

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• How to generate a good random seed to pass to srand()?

  - by zr

  Hi, I am writing a C++ program which needs to create a temporary file for its internal usage. I would like to allow concurrent executions of the program by running multiple proccesses, so the temporary file name needs to be randomized, that way each spawned process will generate a unique temporary file name for its own use. I am using rand() to generate random characters for part of the file name, so i need to initialize the random number generator's seed using srand(). What options are there for passing a good argument to srand() such that two processes will not be initialized with the same seed value? My code needs to work both on Windows and pn Linux TIA.

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• killall httpd for sleep process

  - by user172697

  Hello guys this shell explain the issue , after executing the .sh file halt and nothing happen , any clue where is my mistake its kill httpd if there is more than 10 sleep process and start the httpd with zero sleep process #!/bin/bash #this means loop forever while [ 1 ]; do HTTP=`ps auwxf | grep httpd | grep -v grep | wc -l`; #the above line counts the number of httpd processes found running #and the following line says if there were less then 10 found running if [ $[HTTP] -lt 10 ]; then killall -9 httpd; #inside the if now, so there are less then 10, kill them all and wait 1 second sleep 1; #start apache /etc/init.d/httpd start; fi; #all done, sleep for ten seconds before we loop again sleep 10;done

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• How to achieve high availability?

  - by tanyehzheng

  My boss wants to have a system that takes into concern of continent wide catastrophic event. He wants to have two servers in US and two servers in Asia (1 login server and 1 worker server in each continent). In the event that earthquake breaks the connection between the two continents, both should work alone. When the connection is revived, they should sync each other back to normal. External cloud system not allowed as he has no confidence. The system should take into account of scalability which means addition of new servers should be easy to configure. The servers should be load balanced. The connection between the servers should be very secure(encrypted and send through SSL although SSL takes care of encryption). The system should let one and only one user log in with one account. (beware of latency between continent and two users sharing account may reach both login server at the same time) Please help. I'm already at the end of my wit. Thank you in advance.

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• Measuring daemon CPU utilization over a portion of it's wall clock run time

  - by WhirlWind

  I am dealing with a network-related daemon: it takes data in, processes it, and spits it out. I would like to increase the performance of this daemon by profiling it and reducing it's CPU utilization. I can do this easily on Linux with gprof. However, I would also like to use something like "time" to measure it's total CPU utilization over a period of time. If possible, I would like to time it over a period that is less than its total run time: thus, I would like to start the daemon, wait awhile, generate CPU statistics, stop generating them, then stop the daemon at some later time. The "time" command would work well for me, but it seems to require that I start and stop the daemon as a child of time. Is there a way to measure CPU utilization for only a portion of the daemon's wall clock time?

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• Erlang on a JVM/CLR

  - by Fortyrunner

  I've just started reading Joe Armstrongs book on Erlang and listened to his excellent talk on Software Engineering Radio. Its an interesting language/system and one whose time seems to have come around with the advent of multi-core machines. My question is: what is there to stop it being ported to the JVM or CLR? I realise that both virtual machines aren't setup to run the lightweight processes that Erlang calls for - but couldn't these be simulated by threads? Could we see a lightweight or cutdown version of Erlang on a non Erlang VM?

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• How can I make an expect script prompt for a password?

  - by MiniQuark

  I have an expect script that connects to a few routers through ssh. All these routers have the same password (I know, it's wrong), and the script needs to know that password in order to be able to connect to the routers. Currently, the password is passed to my script as an argument on the command line, but this means that there's a trace of that password in my .bash_history file as well as in the running processes. So instead I would like the user to be prompted for a password, if possible silently. Do you know whether or not it's possible to prompt the user for a password with expect? Thank you. Edit: if I was connecting to servers instead of routers, I would probably use ssh keys instead of passwords. But the routers I'm using just support passwords.

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• SSIS Handling Extenal Issues

  - by durilai

  I have an SSIS package that works fine. The package runs every night and takes about 4 hours to complete. I have am a newb to SSIS, so I want to see what my options are. I am not finding anything on the web about these two issues, so any advice is greatly appreciated. What to do when I have an external issue such as a power failure/accidental restart. Is there a way to alert someone or have the package begin again on restart. A couple weeks ago there was a process that got hung and locked table, making the process not execute. How is the best way to handle ensuring I have the proper access before starting and if not, get the access. I am ok with killing the processes etc. Looking for best practice info. Thanks

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• How To Go About Updating Old C Code

  - by Ben313

  Hello: I have been working on some 10 year old C code at my job this week, and after implementing a few changes, I went to the boss and asked if he needed anything else done. Thats when he dropped the bomb. My next task was to go through the 7000 or so lines and understand more of the code, AND, to modularize the code somewhat. I asked him how he would like the source code modularized, and he said to start putting the old C code into c++ classes. Being a good worker, I nodded my head yes, and went back to my desk, where I sit now, wondering how in the world to take this code, and "modularize" it. Its already in 20 source files, each with its own purpose and function. in addition, there are three "main" structs. each of these stuctures has 30 plus fields, many of them being other, smaller sturcts. Its a complete mess to try to understand, but almost every single function in the program is passed a pointer to one of the structs, and uses the struct heavily. Is there any clean way for me to shoehorn this into classes? I am resolved to do it if it can be done, I just have no idea how to begin.

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• Two BlockingQueue in the same endless loop?

  - by DrDol

  I have a thread, that processes incomming messages (endless loop). For this, I use a BlockingQueue (Java), which works as quite nice. Now, I want to add a second processor in the same Class oder method. The problem now is, that in the endless loop i have this part newIncomming = this.incommingProcessing.take(); This part blocks if the Queue is empty. I'm looking for a solution to process to queues in the same class. The second queue can only processed, it some data is coming in for the first Queue. Is there a way to handle tow blocking queues in the same endless loop?

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• What do you do when you feel you need a variatic list comprehension?

  - by cspyr0

  I would like to make a method where I could give it a list of lengths and it would return all combinations of cartesian coordinates up to those lengths. Easier to explain with an example: cart [2,5] Prelude> [ [0,0],[0,1],[0,2],[0,3],[0,4],[1,0],[1,1],[1,2],[1,3],[1,4] ] cart [2,2,2] Prelude> [ [0,0,0],[0,0,1],[0,1,0],[0,1,1],[1,0,0],[1,0,1],[1,1,0],[1,1,1] ] A simple list comprehension won't work because I don't know how long the lists are going to be. While I love Haskell's simplicity for many problems, this is one that I could write procedurally (in C or something) in 5 minutes whereas Haskell gives me an aneurysm! A solution to this specific problem would help me out a lot; I'd also love to hear about your thought processes when tackling stuff like this.

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• Is there a standard pattern for scanning a job table executing some actions?

  - by Howiecamp

  (I realize that my title is poor. If after reading the question you have an improvement in mind, please either edit it or tell me and I'll change it.) I have the relatively common scenario of a job table which has 1 row for some thing that needs to be done. For example, it could be a list of emails to be sent. The table looks something like this: ID Completed TimeCompleted anything else... ---- --------- ------------- ---------------- 1 No blabla 2 No blabla 3 Yes 01:04:22 ... I'm looking either for a standard practice/pattern (or code - C#/SQL Server preferred) for periodically "scanning" (I use the term "scanning" very loosely) this table, finding the not-completed items, doing the action and then marking them completed once done successfully. In addition to the basic process for accomplishing the above, I'm considering the following requirements: I'd like some means of "scaling linearly", e.g. running multiple "worker processes" simultaneously or threading or whatever. (Just a specific technical thought - I'm assuming that as a result of this requirement, I need some method of marking an item as "in progress" to avoid attempting the action multiple times.) Each item in the table should only be executed once. Some other thoughts: I'm not particularly concerned with the implementation being done in the database (e.g. in T-SQL or PL/SQL code) vs. some external program code (e.g. a standalone executable or some action triggered by a web page) which is executed against the database Whether the "doing the action" part is done synchronously or asynchronously is not something I'm considering as part of this question.

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• Python IPC, popen too slow

  - by UnableToLoad

  i need to run a subprocess (./myProgram) form python script and get output, actually i do this: import subprocess proc = subprocess.Popen('./generate_out', shell=False, stdout=subprocess.PIPE, ) while proc.poll() is None: out = proc.stdout.readline() data = doStuff(out) print(data) but is slow, sometimes pass a lot of time between the output produced by ./generate_out and the print(data), knowing that my doStuff() function is very fast, i think there is some buffer slowing down my pipe... Notes: ./generate_out, generates potentially an unlimited number of lines of finite length each. It seems that when too few chars are put in the pipe between the two processes nothing happens, then when enough is produced i get a huge print (non the expected behaviour!) sometimes i wait many seconds (10-20 and more) between generate_out print and python print) what can i do? maybe communicate() is faster? anithing else? Thank you a lot!

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• Xcodebuild failing to pick up environment values from project file?

  - by egrunin

  I'm using Xcode 3.2.6, MacOSX. I have a globally visible environment setting: ICU_SRC=~/Documents/icu/source This really is an environment setting, it's set at login time. When I open up Terminal, it's there. In my project, under Header Search Paths I've added this: $(ICU_SRC)/i18n $(ICU_SRC)/common These expand correctly when I compile inside the IDE. When I look at the build results, I see this: -I/Users/eric.grunin/Documents/icu/source/i18n -I/Users/eric.grunin/Documents/icu/source/common When I build from the command line, however, it fails. What I see is this: -I/i18n -I/common Here's the command I'm using to compile: /usr/bin/env -i xcodebuild -project my_project.xcodeproj -target "my_program" -configuration Release -sdk macosx10.6 build What am I doing wrong? Edited to add: Apple explains Setting environment variables for user processes

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• Mercurial repository usage with binary files for building setup files

  - by Ryan

  I have an existing Mercurial repository for a C++ application in a small corporate environment. I asked a co-worker to add the setup script to the repository and he added all of the dependency binaries, PDFs, and executable to the repository under an Install directory. I dislike having the binaries and dependencies in the same repository, but I'd like recommendations on best practices. Here are the options I am considering: Create a separate repository for the Installer and related files Create a subrepository for the Installer and related files Use a (yet to be identified) build dependency manager I am concerned with using a subrepository with Mercurial based on what I've read so far and the (apparently) incomplete implementation. I would like to get a project dependency system, e.g. Ivy, but I don't know all of the options and haven't had time yet to try out any options. I thought I'd use TortoiseHg as a basis, and it does not have the TortoiseHg binaries in the repository although it does have some binaries such as kdiff3.exe. Instead it uses setup.py to clone multiple repositories and build the apps. This seems reasonable for OSS, but not so much for corporate environments. Recommendations?

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• How to upload files to server using JSP/Servlet?

  - by Thang Pham

  How can I upload files to server using JSP/Servlet? I tried this: <form action="upload" method="post"> <input type="text" name="description" /> <input type="file" name="file" /> <input type="submit" /> </form> However, I only get the file name, not the file content. When I add enctype="multipart/form-data" to the <form>, then request.getParameter() returns null. During research I stumbled upon Apache Common FileUpload. I tried this: FileItemFactory factory = new DiskFileItemFactory(); ServletFileUpload upload = new ServletFileUpload(factory); List items = upload.parseRequest(request); // This line is where it died. Unfortunately, the servlet threw an exception without a clear message and cause. Here is the stacktrace: SEVERE: Servlet.service() for servlet UploadServlet threw exception javax.servlet.ServletException: Servlet execution threw an exception at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:313) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:852) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Thread.java:637)

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• Can an out-of-process COM object determine its parent process?

  - by Tom Williams

  From an out-of-process COM object (LocalServer32) can I determine the client process that requested the creation of the object? - to be specific I need to get hold of the client processes command line. This question arrises because (due to poor standardisation, implementation and support) the potential 3rd party clients of the object have a variety of idiosyncracies which the object needs to workaround. To do this the object needs to be able to identify its current client. Extending the interface of the COM object so that the client can identify itself is unfortunately not possible ... or to be more precise the interface can be extended but I won't be able to get the clients to call the extension.

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• Load SQL query result data into cache in advance

  - by Marc

  I have the following situation: .net 3.5 WinForm client app accessing SQL Server 2008 Some queries returning relatively big amount of data are used quite often by a form Users are using local SQL Express and restarting their machines at least daily Other users are working remotely over slow network connections The problem is that after a restart, the first time users open this form the queries are extremely slow and take more or less 15s on a fast machine to execute. Afterwards the same queries take only 3s. Of course this comes from the fact that no data is cached and must be loaded from disk first. My question: Would it be possible to force the loading of the required data in advance into SQL Server cache? Note My first idea was to execute the queries in a background worker when the application starts, so that when the user starts the form the queries will already be cached and execute fast directly. I however don't want to load the result of the queries over to the client as some users are working remotely or have otherwise slow networks. So I thought just executing the queries from a stored procedure and putting the results into temporary tables so that nothing would be returned. Turned out that some of the result sets are using dynamic columns so I couldn't create the corresponding temp tables and thus this isn't a solution. Do you happen to have any other idea?

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• Safari doesn't detect my Extension Certificate

  - by Questor

  Hello, all! I have registered for the Safari Development Program and have a valid Apple ID. I've followed all the steps given by Apple. The problem is that Windows XP (Service Pack 2) does not recognize the command 'certreq', whereas the instructions said it would work on any Windows machine. However, the command 'certreq' was working on Windows Vista on the machine of my co-worker's, I downloaded the certificate (the .cer file) and installed it and Safari detected it. However, I don't have Windows Vista. I installed Windows 7 now on my machine, the command 'certreq' works and I have the Safari Extension Certificate (the .cer file) but when I open Safari's Extension Builder, my certificate does not appear there. I entered mmc in Start -- Run and checked if the certificate was installed there. It was in the 'Other People' but not in 'Personal'. Even on Internet Explorer 7+, when I go to Tools -- Internet Options -- Content (Tab) -- Certificates, the certificate is not there in the Personal tab, (WHEREAS IT GOT INSTALLED IN THE PERSONAL FOLDER AUTOMATICALLY IN WINDOWS VISTA). I tried importing the certificate (the .cer file) into the Peronal folder, the import is successful but still neither does it appear in the personal folder nor does Safari recognize/detect it when I go to the Extension Builder. ANY HELP?! I need to make an extension for my office project and the deadline is approaching. I really need to get it done. Thanks a million in anticipation.

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• Python: how to run several scripts (or functions) at the same time under windows 7 multicore processor 64bit

  - by Gianni

  sorry for this question because there are several examples in Stackoverflow. I am writing in order to clarify some of my doubts because I am quite new in Python language. i wrote a function: def clipmyfile(inFile,poly,outFile): ... # doing something with inFile and poly and return outFile Normally I do this: clipmyfile(inFile="File1.txt",poly="poly1.shp",outFile="res1.txt") clipmyfile(inFile="File2.txt",poly="poly2.shp",outFile="res2.txt") clipmyfile(inFile="File3.txt",poly="poly3.shp",outFile="res3.txt") ...... clipmyfile(inFile="File21.txt",poly="poly21.shp",outFile="res21.txt") I had read in this example Run several python programs at the same time and i can use (but probably i wrong) from multiprocessing import Pool p = Pool(21) # like in your example, running 21 separate processes to run the function in the same time and speed my analysis I am really honest to say that I didn't understand the next step. Thanks in advance for help and suggestion Gianni

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• How to signal a buffer full state between posix threads

  - by mikip

  Hi I have two threads, the main thread 'A' is responsible for message handling between a number of processes. When thread A gets a buffer full message, it should inform thread B and pass a pointer to the buffer which thread B will then process. When thread B has finished it should inform thread A that it has finished. How do I go about implementing this using posix threads using C on linux. I have looked at conditional variables, is this the way to go? . I'm not experienced in multi threaded programming and would like some advice on the best avenue to take. Thanks

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