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• Retrieving image from database using Ajax

  - by ama

  I'm trying to read image from database with Ajax, but I could not read the xmlhttp.responseText to the img src. The image is saved as binary data in database and also retrieved as binary data. I'm using Ajax in JSP, because I want to give the user the ability to upload images and I will view the last uploaded image, on mouse over action the Ajax will be activated and get the image back, the problem is in reading the img from the response. This is the Ajax function: function ajaxFunction(path) { if (xmlhttp) { var s = path; xmlhttp.open("GET", s, true); xmlhttp.onreadystatechange = handleServerResponse; xmlhttp.send(null); } } function handleServerResponse() { if (xmlhttp.readyState == 4) { var Image = document.getElementById(Image_Element_Name); document.getElementById(Image_Element_Name).src = "data:" + xmlhttp.responseText; } } I also got exception in the server: 10415315 [TP-Processor1] WARN core.MsgContext - Error sending end packet java.net.SocketException: Broken pipe at java.net.SocketOutputStream.socketWrite0(Native Method) at java.net.SocketOutputStream.socketWrite(SocketOutputStream.java:92) at java.net.SocketOutputStream.write(SocketOutputStream.java:136) at org.apache.jk.common.ChannelSocket.send(ChannelSocket.java:537) at org.apache.jk.common.JkInputStream.endMessage(JkInputStream.java:127) at org.apache.jk.core.MsgContext.action(MsgContext.java:302) at org.apache.coyote.Response.action(Response.java:183) at org.apache.coyote.Response.finish(Response.java:305) at org.apache.catalina.connector.OutputBuffer.close(OutputBuffer.java:281) at org.apache.catalina.connector.Response.finishResponse(Response.java:478) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:154) at org.apache.jk.server.JkCoyoteHandler.invoke(JkCoyoteHandler.java:200) at org.apache.jk.common.HandlerRequest.invoke(HandlerRequest.java:283) at org.apache.jk.common.ChannelSocket.invoke(ChannelSocket.java:773) at org.apache.jk.common.ChannelSocket.processConnection(ChannelSocket.java:703) at org.apache.jk.common.ChannelSocket$SocketConnection.runIt(ChannelSocket.java:895) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:685) at java.lang.Thread.run(Thread.java:619) 10415316 [TP-Processor1] WARN common.ChannelSocket - processCallbacks status 2

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• What are alternatives to Win32 PulseEvent() function?

  - by Bill

  The documentation for the Win32 API PulseEvent() function (kernel32.dll) states that this function is “… unreliable and should not be used by new applications. Instead, use condition variables”. However, condition variables cannot be used across process boundaries like (named) events can. I have a scenario that is cross-process, cross-runtime (native and managed code) in which a single producer occasionally has something interesting to make known to zero or more consumers. Right now, a well-known named event is used (and set to signaled state) by the producer using this PulseEvent function when it needs to make something known. Zero or more consumers wait on that event (WaitForSingleObject()) and perform an action in response. There is no need for two-way communication in my scenario, and the producer does not need to know if the event has any listeners, nor does it need to know if the event was successfully acted upon. On the other hand, I do not want any consumers to ever miss any events. In other words, the system needs to be perfectly reliable – but the producer does not need to know if that is the case or not. The scenario can be thought of as a “clock ticker” – i.e., the producer provides a semi-regular signal for zero or more consumers to count. And all consumers must have the correct count over any given period of time. No polling by consumers is allowed (performance reasons). The ticker is just a few milliseconds (20 or so, but not perfectly regular). Raymen Chen (The Old New Thing) has a blog post pointing out the “fundamentally flawed” nature of the PulseEvent() function, but I do not see an alternative for my scenario from Chen or the posted comments. Can anyone please suggest one? Please keep in mind that the IPC signal must cross process boundries on the machine, not simply threads. And the solution needs to have high performance in that consumers must be able to act within 10ms of each event.

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• when long polling, Why are my other requests taking so long?

  - by Pascal

  The client makes 2 concurrent requests. (1 which takes 60 seconds - long polling) and another which is NOT long polling - supposed to return right away. It does return right away when I'm not doing long polling. But as soon as I start doing long polling with the other thread, the other one takes forever to execute. Firebug shows that the request is waiting for 10-50 seconds. On the server, I profiled ALL requests from the moment the php script starts to the time it goes back to the client, and it shows that each one only took 300ms or less. This problem started about the same time I started doing long polling (with the other XHR requests). I'm using jquery for both requests. The server shows that it is under very light load. CPU and memory less then 2%. 8 processes running out of a pool of 15. (it doesn't seem to deviate much from that number 8, even when I run more ajax requests). I guess each process can run multiple ajax threads concurrently. I made sure to EXIT from all processes as soon as their done executing. I don't see how the process pool has run out, if there are still 7 unused processes listed under prstat -J. Also, the problem happens somewhat intermittently. Firefox should be able to handle 2 concurrent ajax requests. i dont get what the problem is.

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• Flush separate Castle ActiveRecord Transaction, and refresh object in another Transaction

  - by eanticev

  I've got all of my ASP.NET requests wrapped in a Session and a Transaction that gets commited only at the very end of the request. At some point during execution of the request, I would like to insert an object and make it visible to other potential threads - i.e. split the insertion into a new transaction, commit that transaction, and move on. The reason is that the request in question hits an API that then chain hits another one of my pages (near-synchronously) to let me know that it processed, and thus double submits a transaction record, because the original request had not yet finished, and thus not committed the transaction record. So I've tried wrapping the insertion code with a new SessionScope, TransactionScope(TransactionMode.New), combination of both, flushing everything manually, etc. However, when I call Refresh on the object I'm still getting the old object state. Here's some code sample for what I'm seeing: Post outsidePost = Post.Find(id); // status of this post is Status.Old using (TransactionScope transaction = new TransactionScope(TransactionMode.New)) { Post p = Post.Find(id); p.Status = Status.New; // new status set here p.Update(); SessionScope.Current.Flush(); transaction.Flush(); transaction.VoteCommit(); } outsidePost.Refresh(); // refresh doesn't get the new status, status is still Status.Old Any suggestions, ideas, and comments are appreciated!

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• Cocoa Core data: cannot save Created Items in NSTableview

  - by Paul Rostorp

  Hello, I'm am a beginner in mac os x development and am trying to get started with all this. Here is my problem : I've create a non-document based cocoa app using core data as storage. I've added an entity and attributes to the xdatamodel. In IB i've created an NSArrayController and linked it properly. I've created an nstableview binded to the nsarraycontroller. Next I added a button linked to nsarraycontroller with the " add: " method. When I try it out, I can add and edit the items in the table. Here comes the problem: Core data is supposed to save everything automatically, but to make sure i linked the "save" button in the menu to the appdelegate and to the " file's owner" , first responder, application... everything possible ( with both " save :" and " saveaction:" methods ). And still it doesn't save when clicking save: when I restart the cell created ( and renamed ) are gone. And also, I didn't even edit the source code yet; core data for such simple tasks is supposed to only need Interface builder. Please help me for this, I haven't found any threads resolving this problem. Thank you in advance.

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• Google App Engine: Unit testing concurrent access to memcache

  - by Phuong Nguyen de ManCity fan

  Would you guys show me a way to simulating concurrent access to memcache on Google App Engine? I'm trying with LocalServiceTestHelpers and threads but don't have any luck. Every time I try to access Memcache within a thread, then I get this error: ApiProxy$CallNotFoundException: The API package 'memcache' or call 'Increment()' was not found I guess that the testing library of GAE SDK tried to mimic the real environment and thus setup the environment for only one thread (the thread that running the test) which cannot be seen by other thread. Here is a piece of code that can reproduce the problem package org.seamoo.cache.memcacheImpl; import org.testng.Assert; import org.testng.annotations.AfterMethod; import org.testng.annotations.BeforeMethod; import org.testng.annotations.Test; import com.google.appengine.api.memcache.MemcacheService; import com.google.appengine.api.memcache.MemcacheServiceFactory; import com.google.appengine.tools.development.testing.LocalMemcacheServiceTestConfig; import com.google.appengine.tools.development.testing.LocalServiceTestHelper; public class MemcacheTest { LocalServiceTestHelper helper; public MemcacheTest() { LocalMemcacheServiceTestConfig memcacheConfig = new LocalMemcacheServiceTestConfig(); helper = new LocalServiceTestHelper(memcacheConfig); } /** * */ @BeforeMethod public void setUp() { helper.setUp(); } /** * @see LocalServiceTest#tearDown() */ @AfterMethod public void tearDown() { helper.tearDown(); } @Test public void memcacheConcurrentAccess() throws InterruptedException { final MemcacheService service = MemcacheServiceFactory.getMemcacheService(); Runnable runner = new Runnable() { @Override public void run() { // TODO Auto-generated method stub service.increment("test-key", 1L, 1L); try { Thread.sleep(200L); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } service.increment("test-key", 1L, 1L); } }; Thread t1 = new Thread(runner); Thread t2 = new Thread(runner); t1.start(); t2.start(); while (t1.isAlive()) { Thread.sleep(100L); } Assert.assertEquals((Long) (service.get("test-key")), new Long(4L)); } }

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• AsyncTask and Contexts

  - by Michael

  So I'm working out my first multi-threaded application using Android with the AsyncTask class. I'm trying to use it to fire off a Geocoder in a second thread, then update the UI with onPostExecute, but I keep running into an issue with the proper Context. I kind of hobbled my way through using Contexts on the main thread, but I'm not exactly sure what the Context is or how to use it on background threads, and I haven't found any good examples on it. Any help? Here is an excerpt of what I'm trying to do: public class GeoCode extends AsyncTask<GeoThread, Void, GeoThread> { @Override protected GeoThread doInBackground(GeoThread... i) { List<Address> addresses = null; Geocoder geoCode = null; geoCode = new Geocoder(null); //Expects at minimum Geocoder(Context context); addresses = geoCode.getFromLocation(GoldenHour.lat, GoldenHour.lng, 1); } } It keeps failing at the sixth line there, because of the improper Context.

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• Replacing/Extending Visual Studio's Generate Stub in Visual Studio 2010

  - by devoured elysium

  When we write the name of a method that doesn't exist, Visual Studio 2010 asks us if we'd like to generate a method stub with that name. What I'd like to know if is it possible to replace that same code stub generating command with one made by myself. I never did any kind of extensibility programming for Visual Studio so I have a couple of questions: How hard is it? Is it something I can learn in a couple of nights, or is it something that'll make me "lose" a lot of time? It seems to me that there isn't a lot of support for that kind of programming, as generally people are not that interested in developing solutions that extend the Visual Studio IDE. I searched on SO and it doesn't appear to have many threads about extending Visual Studio. I don't know how the generate method stub thing works in Visual Studio, but I just wanted to turn it into something a bit more flexible and useful. Has anyone dealt with these kind of things before, that can give me a pointer to where to start? I know of MS VSX site but that has a lot of resources and can be overwhelming for someone new to the subject as I am. What technology will I need to use? T4? Maybe I'll need to know a lot about the code, like Visual Studio does, so I can know other method's type arguments, names, etc. Is that what T4 is for? Thanks

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• Google Javascript v8 - multithreading

  - by willem

  Hi guys Suppose I have the following piece of code bool run (void) { HandleScope hande_scope; Handle<String> source; Local<Script> script; Persistent<Context> context; context = Context::New(); Context::Scope context_scope(context); script = Script::Compile("var a = 1; var b = 2;"); Local<Value> result = script->Run(); if (result.IsEmpty()) return false; else return true; } Is it true that one cannot execute this code using multiple threads? It seems like HandleScope is not designed to be used in multithreaded applications. I can use the v8::Locker and v8::Unlocker methodes but that would always give me execution traces as this: t1: a = 1 t1: b = 2 t2: a = 1 t2: b = 2 I hope someone can give me a hint on getting this code multithreaded so that a possible execution trace could like this: t1: a = 1 t2: a = 1 t1: b = 2 t2: b = 2 Thanks already in advance! Willem -- EDIT -- So I guess that this question has no answer :)

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• Prerequisites for Account management via an IPhone App?

  - by Icky

  Hello. I have been reading a couple of threads for this topic on this site. I want to create an App, which communicates with a server and has the following features: the User can create/manage an account on the server the App communicates with the server via a secure connection the User is updated about important news through messages From what I understood so far, I need to take care of the following: establish a secure connection with the server send account information(user data, password) to the server and authenticate the client side management and encryption of account data/information is handled by the server, so the App only sends data, the server stores/encrypts (no need for me to take care of anything) So far, I think, I have covered the most important features. I have read, that NSURLConnection can be used, to send the authentication data. But how is further communication ensured? And how is the encryption managed? Are there any useful tutorials on this, because this is the first time I delve into this topic, and any guidance is greatly appreciated! Also, if I have missed anything important (e.g. with managing accounts) please tell me.

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• Linux 2.6.31 Scheduler and Multithreaded Jobs

  - by dsimcha

  I run massively parallel scientific computing jobs on a shared Linux computer with 24 cores. Most of the time my jobs are capable of scaling to 24 cores when nothing else is running on this computer. However, it seems like when even one single-threaded job that isn't mine is running, my 24-thread jobs (which I set for high nice values) only manage to get ~1800% CPU (using Linux notation). Meanwhile, about 500% of the CPU cycles (again, using Linux notation) are idle. Can anyone explain this behavior and what I can do about it to get all of the 23 cores that aren't being used by someone else? Notes: In case it's relevant, I have observed this on slightly different kernel versions, though I can't remember which off the top of my head. The CPU architecture is x64. Is it at all possible that the fact that my 24-core jobs are 32-bit and the other jobs I'm competing w/ are 64-bit is relevant? Edit: One thing I just noticed is that going up to 30 threads seems to alleviate the problem to some degree. It gets me up to ~2100% CPU.

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• question about InnoDB deadlock in MySQL?

  - by WilliamLou

  I found this kind of interesting problem in MySQL InnoDB engine, could anyone explain why the engine always claim it's a deadlock. First, I created a table with a single row, single column: CREATE TABLE `SeqNum` (`current_seq_num` bigint(30) NOT NULL default '0', PRIMARY KEY (`current_seq_num`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | Now, I have two MySQL connector threads, In thread1: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select `current_seq_num` into @curr_seq FROM SeqNum FOR UPDATE; Query OK, 1 row affected (0.00 sec) Now, in thread2, I did the exactly same: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select `current_seq_num` into @curr_seq FROM SeqNum FOR UPDATE; before the default innodb_lock_wait_timeout, the thread2 just wait for thread1 to release its exclusive lock on the table, and it's normal. However, in thread1, if I input the following update query: mysql> update SeqNum set `current_seq_num` = 8; ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction Now, thread2 get the select query finished because thread1 quits. In addition, in thread1, if I input the update query with a where clause, it can be executed very well: mysql> update SeqNum set `current_seq_num` = 8 where `current_seq_num` =5 Query OK, 1 row affected (0.00 sec) Could anyone explain this?

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• Cooperative/Non-preemptive threading avoiding threadlooks?

  - by Wayne

  Any creative ideas to avoid deadlocks on a yield or sleep with cooperative/non-preemptive multitasking without doing an O/S Thread.Sleep(10)? Typically the yield or sleep call will call back into the scheduler to run other tasks. But this can sometime produce deadlocks. Some background: This application has enormous need for speed and, so far, it's extremely fast as compared to other systems in the same industry. One of the speed techniques is cooperative/non-preemptive threading rather then the cost of a context switch from O/S threads. The high level design a priority manager which calls out to tasks depending on priority and processing time. Each task does one "iteration" of work and returns to wait its turn again in the priority queue. The tricky thing with non-preemptive threading is what to do when you want to a particular task to stop in the middle of work and wait for some other event from a different task before continuing. In this case, we have 3 tasks, A B and C where A is a controller that must synchronize the activity of B and C. First, A starts both B and C. Then B yields so C gets invoked. When C yields, A sees they are both inactive, decides it's time for B to run but not time for C yet. Well B is now stuck in a yield that has called C, so it can never run. Sincerely, Wayne

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• sh: dot: command not found + doxygen + Lion

  - by Salil

  MacOS version : 10.7.2 ( lion ) Doxygen version : 1.7.5.1 Graphviz version : 2.29 Doxygen configuration - DOT_PATH = ../../../../Applications/Contents/MacOS/Graphviz HAVE_DOT = YES SHORT_NAMES = YES From the log console - First line it gives a warning - warning: the dot tool could not be found at ../../../../Applications/Contents/MacOS/Graphviz - I have tried various combinations but the warning does not go , although it generates the images. Generating dot graphs using 9 parallel threads... Running dot for graph 1/68 sh: dot: command not found Problems running dot: exit code=127, command='dot', arguments='"/Users/salilk/Documents/project/DoxygenDocs/html/a00033.dot" -Tpng -o "/Users/salilk/Documents/project/DoxygenDocs/html/a00033.png"' In the html directory the .dot files have been generated but no .png. Now if I execute the same command from the Terminal the .png file gets generated and is displayed in its .html file. Another error from the console is - error: problems opening map file /Users/salilk/Documents/A2O Collaborate/DoxygenDocs/html/a00032.map for inclusion in the docs! If you installed Graphviz/dot after a previous failing run, try deleting the output directory and rerun doxygen. - Is this related to the above problem ? I have used Doxygen before on a Windows machine and didn't have these errors , do we need to do any configurations specific for Mac ? - Salil.

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• How to use SQLAlchemy to dump an SQL file from query expressions to bulk-insert into a DBMS?

  - by Mahmoud Abdelkader

  Please bear with me as I explain the problem, how I tried to solve it, and my question on how to improve it is at the end. I have a 100,000 line csv file from an offline batch job and I needed to insert it into the database as its proper models. Ordinarily, if this is a fairly straight-forward load, this can be trivially loaded by just munging the CSV file to fit a schema, but I had to do some external processing that requires querying and it's just much more convenient to use SQLAlchemy to generate the data I want. The data I want here is 3 models that represent 3 pre-exiting tables in the database and each subsequent model depends on the previous model. For example: Model C --> Foreign Key --> Model B --> Foreign Key --> Model A So, the models must be inserted in the order A, B, and C. I came up with a producer/consumer approach: - instantiate a multiprocessing.Process which contains a threadpool of 50 persister threads that have a threadlocal connection to a database - read a line from the file using the csv DictReader - enqueue the dictionary to the process, where each thread creates the appropriate models by querying the right values and each thread persists the models in the appropriate order This was faster than a non-threaded read/persist but it is way slower than bulk-loading a file into the database. The job finished persisting after about 45 minutes. For fun, I decided to write it in SQL statements, it took 5 minutes. Writing the SQL statements took me a couple of hours, though. So my question is, could I have used a faster method to insert rows using SQLAlchemy? As I understand it, SQLAlchemy is not designed for bulk insert operations, so this is less than ideal. This follows to my question, is there a way to generate the SQL statements using SQLAlchemy, throw them in a file, and then just use a bulk-load into the database? I know about str(model_object) but it does not show the interpolated values. I would appreciate any guidance for how to do this faster. Thanks!

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• HttpWebRequest Timeouts After Ten Consecutive Requests

  - by Bob Mc

  I'm writing a web crawler for a specific site. The application is a VB.Net Windows Forms application that is not using multiple threads - each web request is consecutive. However, after ten successful page retrievals every successive request times out. I have reviewed the similar questions already posted here on SO, and have implemented the recommended techniques into my GetPage routine, shown below: Public Function GetPage(ByVal url As String) As String Dim result As String = String.Empty Dim uri As New Uri(url) Dim sp As ServicePoint = ServicePointManager.FindServicePoint(uri) sp.ConnectionLimit = 100 Dim request As HttpWebRequest = WebRequest.Create(uri) request.KeepAlive = False request.Timeout = 15000 Try Using response As HttpWebResponse = DirectCast(request.GetResponse, HttpWebResponse) Using dataStream As Stream = response.GetResponseStream() Using reader As New StreamReader(dataStream) If response.StatusCode <> HttpStatusCode.OK Then Throw New Exception("Got response status code: " + response.StatusCode) End If result = reader.ReadToEnd() End Using End Using response.Close() End Using Catch ex As Exception Dim msg As String = "Error reading page """ & url & """. " & ex.Message Logger.LogMessage(msg, LogOutputLevel.Diagnostics) End Try Return result End Function Have I missed something? Am I not closing or disposing of an object that should be? It seems strange that it always happens after ten consecutive requests. Notes: In the constructor for the class in which this method resides I have the following: ServicePointManager.DefaultConnectionLimit = 100 If I set KeepAlive to true, the timeouts begin after five requests. All the requests are for pages in the same domain. EDIT I added a delay between each web request of between two and seven seconds so that I do not appear to be "hammering" the site or attempting a DOS attack. However, the problem still occurs.

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• UIScrollView notifications

  - by ryyst

  Hi, I'm coding an app that works much like Apple's Weather.app: There's a UIPageControl at the bottom and a UIScrollView in the middle of the screen. In my code, I implemented the - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView method to figure out when the user did move to a new page. If they move to a new page, I load the adjacent pages' data, as to make further page-switching faster. (In one of Apple's examples, the - (void)scrollViewDidScroll:(UIScrollView *)sender is used, but that causes my app to shortly hang when loading a new page, so it's not suitable.) That code works very well. I'm using scrollRectToVisible:: to programmatically scroll inside the scrollview when the user clicks the UIPageControl. The problem is that the scrollRectToVisible: doesn't post a notification to the UIScrollViewDelegate when it's done scrolling - so the code responsible for loading adjacent pages never get's called when using the UIPageControl. Is there any way to make the UIScrollView notify its delegate when it gets called by the scrollRectToVisible: method? Or will I have to use threads in order to prevent my app from freezing? Thanks! -- Ry

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• cx_Oracle makes subprocess give OSError

  - by Shrikant Sharat

  I am trying to use the cx_Oracle module with python 2.6.6 on ubuntu Maverick, with Oracle 11gR2 Enterprise edition. I am able to connect to my oracle db just fine, but once I do that, the subprocess module does not work anymore. Here is an iPython session that reproduces the problem... In [1]: import subprocess as sp, cx_Oracle as dbh In [2]: sp.call(['whoami']) sharat Out[2]: 0 In [3]: con = dbh.connect('system', 'password') In [4]: con.close() In [5]: sp.call(['whomai']) --------------------------------------------------------------------------- OSError Traceback (most recent call last) /home/sharat/desk/calypso-launcher/<ipython console> in <module>() /usr/lib/python2.6/subprocess.pyc in call(*popenargs, **kwargs) 468 retcode = call(["ls", "-l"]) 469 """ --> 470 return Popen(*popenargs, **kwargs).wait() 471 472 /usr/lib/python2.6/subprocess.pyc in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags) 621 p2cread, p2cwrite, 622 c2pread, c2pwrite, --> 623 errread, errwrite) 624 625 if mswindows: /usr/lib/python2.6/subprocess.pyc in _execute_child(self, args, executable, preexec_fn, close_fds, cwd, env, universal_newlines, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite) 1134 1135 if data != "": -> 1136 _eintr_retry_call(os.waitpid, self.pid, 0) 1137 child_exception = pickle.loads(data) 1138 for fd in (p2cwrite, c2pread, errread): /usr/lib/python2.6/subprocess.pyc in _eintr_retry_call(func, *args) 453 while True: 454 try: --> 455 return func(*args) 456 except OSError, e: 457 if e.errno == errno.EINTR: OSError: [Errno 10] No child processes So, the call to sp.call works fine before connecting to oracle, but breaks after that. Even if I have closed the connection to the database. Looking around, I found http://bugs.python.org/issue1731717 as somewhat related to this issue, but I am not dealing with threads here. I don't know if cx_Oracle is. Moreover, the above issue mentions that adding a time.sleep(1) fixes it, but it didn't help me. Any help appreciated. Thanks.

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• Python Socket Getting Connection Reset

  - by Ian

  I created a threaded socket listener that stores newly accepted connections in a queue. The socket threads then read from the queue and respond. For some reason, when doing benchmarking with 'ab' (apache benchmark) using a concurrency of 2 or more, I always get a connection reset before it's able to complete the benchmark (this is taking place locally, so there's no external connection issue). class server: _ip = '' _port = 8888 def __init__(self, ip=None, port=None): if ip is not None: self._ip = ip if port is not None: self._port = port self.server_listener(self._ip, self._port) def now(self): return time.ctime(time.time()) def http_responder(self, conn, addr): httpobj = http_builder() httpobj.header('HTTP/1.1 200 OK') httpobj.header('Content-Type: text/html; charset=UTF-8') httpobj.header('Connection: close') httpobj.body("Everything looks good") data = httpobj.generate() sent = conn.sendall(data) def http_thread(self, id): self.log("THREAD %d: Starting Up..." % id) while True: conn, addr = self.q.get() ip, port = addr self.log("THREAD %d: responding to request: %s:%s - %s" % (id, ip, port, self.now())) self.http_responder(conn, addr) self.q.task_done() conn.close() def server_listener(self, host, port): self.q = Queue.Queue(0) sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) sock.bind( (host, port) ) sock.listen(5) for i in xrange(4): #thread count thread.start_new(self.http_thread, (i+1, )) while True: self.q.put(sock.accept()) sock.close() server('', 9999) When running the benchmark, I get totally random numbers of good requests before it errors out, usually between 4 and 500. Edit: Took me a while to figure it out, but the problem was in sock.listen(5). Because I was using apache benchmark with a higher concurrency (5 and up) it was causing the backlog of connections to pile up, at which point the connections started getting dropped by the socket.

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• Blocking on DBCP connection pool (open and close connnection). Is database connection pooling in OpenEJB pluggable?

  - by topchef

  We use OpenEJB on Tomcat (used to run on JBoss, Weblogic, etc.). While running load tests we experience significant performance problems with handling JMS messages (queues). Problem was localized to blocking on database connection pool getting or releasing connection to the pool. Blocking prevented concurrent MDB instances (threads) from running hence performance suffered 10-fold and worse. The same code used to run on application servers (with their respective connection pool implementations) with no blocking at all. Example of thread blocked: Name: JMS Resource Adapter-worker-23 State: BLOCKED on org.apache.commons.pool.impl.GenericObjectPool@1ea6b4a owned by: JMS Resource Adapter-worker-19 Total blocked: 18,426 Total waited: 0 Stack trace: org.apache.commons.pool.impl.GenericObjectPool.returnObject(GenericObjectPool.java:916) org.apache.commons.dbcp.PoolableConnection.close(PoolableConnection.java:91) - locked org.apache.commons.dbcp.PoolableConnection@1bcba8 org.apache.commons.dbcp.managed.ManagedConnection.close(ManagedConnection.java:147) com.xxxxx.persistence.DbHelper.closeConnection(DbHelper.java:290) .... Couple of questions. I am almost certain that some transactional attributes and properties contribute to this blocking, but MDBs are defined as non-transactional (we use both annotations and ejb-jar.xml). Some EJBs do use container-managed transactions though (and we can observe blocking there as well). Are there any DBCP configurations that may fix blocking? Is DBCP connection pool implementation replaceable in OpenEJB? How easy (difficult) to replace it with another library? Just in case this is how we define data source in OpenEJB (openejb.xml): <Resource id="MyDataSource" type="DataSource"> JdbcDriver oracle.jdbc.driver.OracleDriver JdbcUrl ${oracle.jdbc} UserName ${oracle.user} Password ${oracle.password} JtaManaged true InitialSize 5 MaxActive 30 ValidationQuery SELECT 1 FROM DUAL TestOnBorrow true </Resource>

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• How can I implement a proper counter bean with EJB 3.0?

  - by Aaron Digulla

  I have this entity bean: import javax.persistence.*; @Entity public class CounterTest { private int id; private int counter; @Id public int getId() { return id; } public void setId(int id) { this.id = id; } public int getCounter() { return counter; } public void setCounter(int counter) { this.counter = counter; } } and this stateful bean to increment a counter: import java.rmi.RemoteException; import javax.ejb.*; import javax.persistence.*; @Stateful public class CounterTestBean implements CounterTestRemote { @PersistenceContext(unitName = "JavaEE") EntityManager manager; public void initDB() { CounterTest ct = new CounterTest(); ct.setNr(1); ct.setWert(1); manager.persist(ct); } public boolean testCounterWithLock() { try { CounterTest ct = manager.find(CounterTest.class, 1); manager.lock(ct, LockModeType.WRITE); int wert = ct.getWert(); ct.setWert(wert + 1); manager.flush(); return true; } catch (Throwable t) { return false; } } } When I call testCounterWithLock() from three threads 500 times each, the counter gets incremented between 13 and 1279 times. How do I fix this code so that it is incremented 1500 times?

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• Stream Reuse in C#

  - by MikeD

  I've been playing around with what I thought was a simple idea. I want to be able to read in a file from somewhere (website, filesystem, ftp), perform some operations on it (compress, encrypt, etc.) and then save it somewhere (somewhere may be a filesystem, ftp, or whatever). It's a basic pipeline design. What I would like to do is to read in the file and put it onto a MemoryStream, then perform the operations on the data in the MemoryStream, and then save that data in the MemoryStream somewhere. I was thinking I could use the same Stream to do this but run into a couple of problems: Everytime I use a StreamWriter or StreamReader I need to close it and that closes the stream so that I cannot use it anymore. That seems like there must be some way to get around that. Some of these files may be big and so I may run out of memory if I try to read the whole thing in at once. I was hoping to be able to spin up each of the steps as separate threads and have the compression step begin as soon as there is data on the stream, and then as soon as the compression has some compressed data available on the stream I could start saving it (for example). Is anything like this easily possible with the C# Streams? ANyone have thoughts as to how to accomplish this best? Thanks, Mike

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• Semaphore race condition?

  - by poindexter12

  I have created a "Manager" class that contains a limited set of resources. The resources are stored in the "Manager" as a Queue. I initialize the Queue and a Semaphore to the same size, using the semaphore to block a thread if there are no resources available. I have multiple threads calling into this class to request a resource. Here is the psuedo code: public IResource RequestResource() { IResource resource = null; _semaphore.WaitOne(); lock (_syncLock) { resource = _resources.Dequeue(); } return resource; } public void ReleaseResource(IResource resource) { lock (_syncLock) { _resources.Enqueue(resource); } _semaphore.Release(); } While running this application, it seems to run fine for a while. Then, it seems like my Queue is giving out the same object. Does this seem like its possible? I'm pulling my hair out over here, and any help would be greatly appreciated. Feel free to ask for more information if you need it. Thanks!

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• Makefile : Build in a separate directory tree

  - by Simone Margaritelli

  My project (an interpreted language) has a standard library composed by multiple files, each of them will be built into an .so dynamic library that the interpreter will load upon user request (with an import directive). Each source file is located into a subdirectory representing its "namespace", for instance : The build process has to create a "build" directory, then when each file is compiling has to create its namespace directory inside the "build" one, for instance, when compiling std/io/network/tcp.cc he run an mkdir command with mkdir -p build/std/io/network The Makefile snippet is : STDSRC=stdlib/std/hashing/md5.cc \ stdlib/std/hashing/crc32.cc \ stdlib/std/hashing/sha1.cc \ stdlib/std/hashing/sha2.cc \ stdlib/std/io/network/http.cc \ stdlib/std/io/network/tcp.cc \ stdlib/std/io/network/smtp.cc \ stdlib/std/io/file.cc \ stdlib/std/io/console.cc \ stdlib/std/io/xml.cc \ stdlib/std/type/reflection.cc \ stdlib/std/type/string.cc \ stdlib/std/type/matrix.cc \ stdlib/std/type/array.cc \ stdlib/std/type/map.cc \ stdlib/std/type/type.cc \ stdlib/std/type/binary.cc \ stdlib/std/encoding.cc \ stdlib/std/os/dll.cc \ stdlib/std/os/time.cc \ stdlib/std/os/threads.cc \ stdlib/std/os/process.cc \ stdlib/std/pcre.cc \ stdlib/std/math.cc STDOBJ=$(STDSRC:.cc=.so) all: stdlib stdlib: $(STDOBJ) .cc.so: mkdir -p `dirname $< | sed -e 's/stdlib/stdlib\/build/'` $(CXX) $< -o `dirname $< | sed -e 's/stdlib/stdlib\/build/'`/`basename $< .cc`.so $(CFLAGS) $(LDFLAGS) I have two questions : 1 - The problem is that the make command, i really don't know why, doesn't check if a file was modified and launch the build process on ALL the files no matter what, so if i need to build only one file, i have to build them all or use the command : make path/to/single/file.so Is there any way to solve this? 2 - Any way to do this in a "cleaner" way without have to distribute all the build directories with sources? Thanks

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• Looking for merge tool with very good in-line-comparison support

  - by peter p

  I have seen this topic discussed several times, but emphasis is on "very good in-line-comparison" here, which was not really covered by those threads. E.g. I would like the tool to recognize and highlight that the resource "colorpicker_newstring" has been added when comparing the following two blocks. WinMerge and Kdiff both fail... Does anyone know a software that does not? I am using Windows. Ah, and I'd prefer free/OS software, of course. Thanks a lot in advance, Peter File A: <resource name="colorpicker_title">Color picker</resource> <resource name="colorpicker_apply">Apply</resource> <resource name="colorpicker_transparent">Transparent</resource> <resource name="colorpicker_htmlcolor">HTML color</resource> <resource name="colorpicker_red">Red</resource> <resource name="colorpicker_newstring">New String</resource> <resource name="colorpicker_green">Green</resource> <resource name="colorpicker_blue">Blue</resource> <resource name="colorpicker_alpha">Alpha</resource> <resource name="colorpicker_recentcolors">Recently used colors</resource> File B: <resource name="colorpicker_title">Sélecteur de couleur</resource> <resource name="colorpicker_apply">Appliquer</resource> <resource name="colorpicker_transparent">Transparent</resource> <resource name="colorpicker_htmlcolor">Couleur HTML</resource> <resource name="colorpicker_red">Rouge</resource> <resource name="colorpicker_green">Vert</resource> <resource name="colorpicker_blue">Bleu</resource> <resource name="colorpicker_alpha">Alpha</resource> <resource name="colorpicker_recentcolors">Couleurs récentes</resource>

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