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• How to handle all unhandled exceptions when using Task Parallel Library?

  - by Buu Nguyen

  I'm using the TPL (Task Parallel Library) in .NET 4.0. I want to be able to centralize the handling logic of all unhandled exceptions by using the Thread.GetDomain().UnhandledException event. However, in my application, the event is never fired for threads started with TPL code, e.g. Task.Factory.StartNew(...). The event is indeed fired if I use something like new Thread(threadStart).Start(). This MSDN article suggests to use Task#Wait() to catch the AggregateException when working with TPL, but that is not I want because it is not "centralized" enough a mechanism. Does anyone experience same problem at all or is it just me? Do you have any solution for this?

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• Handling Incoming Data from Multiple Sockets in Python

  - by user859434

  Background: I have a current implementation that receives data from about 120 different socket connections in python. In my current implementation, I handle each of these separate socket connections with a dedicated thread for each. Each of these threads parse the data and eventually store it within a shared locked dictionary. These sockets DO NOT have uniform data rates, some sockets get more data than others. Question: Is this the best way to handle incoming data in python, or does python have a better way on handling multiple sockets per thread?

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• Explicit call of Runnable.run

  - by klaudio

  Hi, I have a question. Somebody, who was working on my code before me, created some method and passed Runnable as parameter, more likely: void myMethod(Runnable runnable){ runnable.run(); } Then calling myMethod out of main looks like: public static void main(String args[]) { try { myMethod(new Runnable(){ public void run() { //do something...; }}); } catch (Throwable t) { } } So, to supply parameter to myMethod I need to instantiate object of (in this case anonymous) class implementing Runnable. My question is: is it necessary to use Runnable in this example? Can I use any different interface? I mean I can create new interface with single method i.e. interface MyInterface{ void doThis(); } then change look of myMethod: void myMethod(MyInterface myObject){ myObject.doThis(); } And of course client too: public static void main(String args[]) { try { myMethod(new MyInterface (){ public void doThis() { //do something...; }}); } catch (Throwable t) { } } Or maybe something is about Runnable?!

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• .NET threading: how can I capture an abort on an unstarted thread?

  - by Groxx

  I have a chunk of threads I wish to run in order, on an ASP site running .NET 2.0 with Visual Studio 2008 (no idea how much all that matters, but there it is), and they may have aborted-clean-up code which should be run regardless of how far through their task they are. So I make a thread like this: Thread t = new Thread(delegate() { try { /* do things */ System.Diagnostics.Debug.WriteLine("try"); } catch (ThreadAbortException) { /* cleanup */ System.Diagnostics.Debug.WriteLine("catch"); } }); Now, if I wish to abort the set of threads part way through, the cleanup may still be desirable later on down the line. Looking through MSDN implies you can .Abort() a thread that has not started, and then .Start() it, at which point it will receive the exception and perform normally. Or you can .Join() the aborted thread to wait for it to finish aborting. Presumably you can combine them. http://msdn.microsoft.com/en-us/library/ty8d3wta(v=VS.80).aspx To wait until a thread has aborted, you can call the Join method on the thread after calling the Abort method, but there is no guarantee the wait will end. If Abort is called on a thread that has not been started, the thread will abort when Start is called. If Abort is called on a thread that is blocked or is sleeping, the thread is interrupted and then aborted. Now, when I debug and step through this code: t.Abort(); // ThreadState == Unstarted | AbortRequested t.Start(); // throws ThreadStartException: "Thread failed to start." // so I comment it out, and t.Join(); // throws ThreadStateException: "Thread has not been started." At no point do I see any output, nor do any breakpoints on either the try or catch block get reached. Oddly, ThreadStartException is not listed as a possible throw of .Start(), from here: http://msdn.microsoft.com/en-us/library/a9fyxz7d(v=VS.80).aspx (or any other version) I understand this could be avoided by having a start parameter, which states if the thread should jump to cleanup code, and foregoing the Abort call (which is probably what I'll do). And I could .Start() the thread, and then .Abort() it. But as an indeterminate amount of time may pass between .Start and .Abort, I'm considering it unreliable, and the documentation seems to say my original method should work. Am I missing something? Is the documentation wrong? edit: ow. And you can't call .Start(param) on a non-parameterized Thread(Start). Is there a way to find out if a thread is parameterized or not, aside from trial and error? I see a private m_Delegate, but nothing public...

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• can a python script know that another instance of the same script is running... and then talk to it?

  - by Justin Grant

  I'd like to prevent multiple instances of the same long-running python command-line script from running at the same time, and I'd like the new instance to be able to send data to the original insance before the new instance commits suicide. How can I do this in a cross-platform way? Specifically, I'd like to enable the following behavior: "foo.py" is launched from the command line, and it will stay running for a long time-- days or weeks until the machine is rebooted or the parent process kills it. every few minutes the same script is launched again, but with different command-line parameters when launched, the script should see if any other instances are running. if other instances are running, then instance #2 should send its command-line parameters to instance #1, and then instance #2 should exit. instance #1, if it receives command-line parameters from another script, should spin up a new thread and (using the command-line parameters sent in the step above) start performing the work that instance #2 was going to perform. So I'm looking for two things: how can a python program know another instance of itself is running, and then how can one python command-line program communicate with another? Making this more complicated, the same script needs to run on both Windows and Linux, so ideally the solution would use only the Python standard library and not any OS-specific calls. Although if I need to have a Windows codepath and an *nix codepath (and a big if statement in my code to choose one or the other), that's OK if a "same code" solution isn't possible. I realize I could probably work out a file-based approach (e.g. instance #1 watches a directory for changes and each instance drops a file into that directory when it wants to do work) but I'm a little concerned about cleaning up those files after a non-graceful machine shutdown. I'd ideally be able to use an in-memory solution. But again I'm flexible, if a persistent-file-based approach is the only way to do it, I'm open to that option. More details: I'm trying to do this because our servers are using a monitoring tool which supports running python scripts to collect monitoring data (e.g. results of a database query or web service call) which the monitoring tool then indexes for later use. Some of these scripts are very expensive to start up but cheap to run after startup (e.g. making a DB connection vs. running a query). So we've chosen to keep them running in an infinite loop until the parent process kills them. This works great, but on larger servers 100 instances of the same script may be running, even if they're only gathering data every 20 minutes each. This wreaks havoc with RAM, DB connection limits, etc. We want to switch from 100 processes with 1 thread to one process with 100 threads, each executing the work that, previously, one script was doing. But changing how the scripts are invoked by the monitoring tool is not possible. We need to keep invocation the same (launch a process with different command-line parameters) but but change the scripts to recognize that another one is active, and have the "new" script send its work instructions (from the command line params) over to the "old" script.

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• Is a new thread in a Visual Studio test project aborted when the test ends?

  - by Michel

  Hi, i have to do some message exchange with a 3rd party (in a website). When the client posts a page, i start the message exchange. When that doesn't succeed for some reason, i report this to the client by rendering the page with a message. On the background, in a separate thread, i start a process to send abort messages to the 3rd party. I can't do this while the user is waiting for the page to come back, because it might take a few minutes. But in a test project, the test ends when the message to the 3rd party is sent, and after the new thread is started. But it seems that the new thread also ends, when the test is done. Is that normal behaviour? I do start the thread in a new class with a reference to 2 objects from the class which tries to send the message in the first place, may that be a problem?

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• BackgroundWorker

  - by vdh_ant

  Hi guys I'm working on some code that calls a service. This service call could fail and if it does I want the system to try again until it works or too much time has passed. I am wondering where I am going wrong as the following code doesn't seem to be working correctly... It randomly only does one to four loops... protected virtual void ProcessAsync(object data, int count) { var worker = new BackgroundWorker(); worker.DoWork += (sender, e) => { throw new InvalidOperationException("oh shiznit!"); }; worker.RunWorkerCompleted += (sender, e) => { //If an error occurs we need to tell the data about it if (e.Error != null) { count++; System.Threading.Thread.Sleep(count * 5000); if (count <= 10) { if (count % 5 == 0) this.Logger.Fatal("LOAD ERROR - The system can't load any data", e.Error); else this.Logger.Error("LOAD ERROR - The system can't load any data", e.Error); this.ProcessAsync(data, count); } } }; worker.RunWorkerAsync(); } Cheers Anthony

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• Do something else if ReadWriteSlimlock is held

  - by user43838

  Hi everyone, I have implemented ReaderWriterLockSlim, Now i don't want it to wait at the lock. I want to do something else if the lock is held. I considered using is isWriterLockHeld but it does not makes much sense to me, Since if two threads come in at the same time and enter the if statement at the same time one will still be waiting at the lock here is my code. ReaderWriterLockSlim rw = GetLoadingLock(parameters); rw = GetLoadingLock(parameters); try { rw.EnterWriteLock(); item = this.retrieveCacheItem(parameters.ToString(), false); if (item != null) { parameters.DataCameFromCache = true; // if the data was found in the cache, return it immediately return item.data; } else { try { object loaditem = null; itemsLoading[parameters.ToString()] = true; loaditem = this.retrieveDataFromStore(parameters); return loaditem; } finally { itemsLoading.Remove(parameters.ToString()); } } } finally { rw.ExitWriteLock(); } Can anyone please guide me in the right direction with this. Thanks

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• Does an asynchronous call always create/call a new thread?

  - by Ted Smith

  Does asynchronous call always create a new thread? Example: If Javascript is single threaded then how can it do an async postback? Is it actually blocking until it gets a callback? If so, is this really an async call?

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• Fixed strptime exception with thread lock, but slows down the program

  - by eWizardII

  I have the following code, which when is running inside of a thread (the full code is here - https://github.com/eWizardII/homobabel/blob/master/lovebird.py) for null in range(0,1): while True: try: with open('C:/Twitter/tweets/user_0_' + str(self.id) + '.json', mode='w') as f: f.write('[') threadLock.acquire() for i, seed in enumerate(Cursor(api.user_timeline,screen_name=self.ip).items(200)): if i>0: f.write(", ") f.write("%s" % (json.dumps(dict(sc=seed.author.statuses_count)))) j = j + 1 threadLock.release() f.write("]") except tweepy.TweepError, e: with open('C:/Twitter/tweets/user_0_' + str(self.id) + '.json', mode='a') as f: f.write("]") print "ERROR on " + str(self.ip) + " Reason: ", e with open('C:/Twitter/errors_0.txt', mode='a') as a_file: new_ii = "ERROR on " + str(self.ip) + " Reason: " + str(e) + "\n" a_file.write(new_ii) break Now without the thread lock I generate the following error: Exception in thread Thread-117: Traceback (most recent call last): File "C:\Python27\lib\threading.py", line 530, in __bootstrap_inner self.run() File "C:/Twitter/homobabel/lovebird.py", line 62, in run for i, seed in enumerate(Cursor(api.user_timeline,screen_name=self.ip).items(200)): File "build\bdist.win-amd64\egg\tweepy\cursor.py", line 110, in next self.current_page = self.page_iterator.next() File "build\bdist.win-amd64\egg\tweepy\cursor.py", line 85, in next items = self.method(page=self.current_page, *self.args, **self.kargs) File "build\bdist.win-amd64\egg\tweepy\binder.py", line 196, in _call return method.execute() File "build\bdist.win-amd64\egg\tweepy\binder.py", line 182, in execute result = self.api.parser.parse(self, resp.read()) File "build\bdist.win-amd64\egg\tweepy\parsers.py", line 75, in parse result = model.parse_list(method.api, json) File "build\bdist.win-amd64\egg\tweepy\models.py", line 38, in parse_list results.append(cls.parse(api, obj)) File "build\bdist.win-amd64\egg\tweepy\models.py", line 49, in parse user = User.parse(api, v) File "build\bdist.win-amd64\egg\tweepy\models.py", line 86, in parse setattr(user, k, parse_datetime(v)) File "build\bdist.win-amd64\egg\tweepy\utils.py", line 17, in parse_datetime date = datetime(*(time.strptime(string, '%a %b %d %H:%M:%S +0000 %Y')[0:6])) File "C:\Python27\lib\_strptime.py", line 454, in _strptime_time return _strptime(data_string, format)[0] File "C:\Python27\lib\_strptime.py", line 300, in _strptime _TimeRE_cache = TimeRE() File "C:\Python27\lib\_strptime.py", line 188, in __init__ self.locale_time = LocaleTime() File "C:\Python27\lib\_strptime.py", line 77, in __init__ raise ValueError("locale changed during initialization") ValueError: locale changed during initialization The problem is with thread lock on, each thread runs itself serially basically, and it takes way to long for each loop to run for there to be any advantage to having a thread anymore. So if there isn't a way to get rid of the thread lock, is there a way to have it run the for loop inside of the try statement faster?

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• What limits scaling in this simple OpenMP program?

  - by Douglas B. Staple

  I'm trying to understand limits to parallelization on a 48-core system (4xAMD Opteron 6348, 2.8 Ghz, 12 cores per CPU). I wrote this tiny OpenMP code to test the speedup in what I thought would be the best possible situation (the task is embarrassingly parallel): // Compile with: gcc scaling.c -std=c99 -fopenmp -O3 #include <stdio.h> #include <stdint.h> int main(){ const uint64_t umin=1; const uint64_t umax=10000000000LL; double sum=0.; #pragma omp parallel for reduction(+:sum) for(uint64_t u=umin; u<umax; u++) sum+=1./u/u; printf("%e\n", sum); } I was surprised to find that the scaling is highly nonlinear. It takes about 2.9s for the code to run with 48 threads, 3.1s with 36 threads, 3.7s with 24 threads, 4.9s with 12 threads, and 57s for the code to run with 1 thread. Unfortunately I have to say that there is one process running on the computer using 100% of one core, so that might be affecting it. It's not my process, so I can't end it to test the difference, but somehow I doubt that's making the difference between a 19~20x speedup and the ideal 48x speedup. To make sure it wasn't an OpenMP issue, I ran two copies of the program at the same time with 24 threads each (one with umin=1, umax=5000000000, and the other with umin=5000000000, umax=10000000000). In that case both copies of the program finish after 2.9s, so it's exactly the same as running 48 threads with a single instance of the program. What's preventing linear scaling with this simple program?

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• Thread sleep and thread join.

  - by Dhruv Gairola

  hi guys, if i put a thread to sleep in a loop, netbeans gives me a caution saying Invoking Thread.sleep in loop can cause performance problems. However, if i were to replace the sleep with join, no such caution is given. Both versions compile and work fine tho. My code is below (check the last few lines for "Thread.sleep() vs t.join()"). public class Test{ //Display a message, preceded by the name of the current thread static void threadMessage(String message) { String threadName = Thread.currentThread().getName(); System.out.format("%s: %s%n", threadName, message); } private static class MessageLoop implements Runnable { public void run() { String importantInfo[] = { "Mares eat oats", "Does eat oats", "Little lambs eat ivy", "A kid will eat ivy too" }; try { for (int i = 0; i < importantInfo.length; i++) { //Pause for 4 seconds Thread.sleep(4000); //Print a message threadMessage(importantInfo[i]); } } catch (InterruptedException e) { threadMessage("I wasn't done!"); } } } public static void main(String args[]) throws InterruptedException { //Delay, in milliseconds before we interrupt MessageLoop //thread (default one hour). long patience = 1000 * 60 * 60; //If command line argument present, gives patience in seconds. if (args.length > 0) { try { patience = Long.parseLong(args[0]) * 1000; } catch (NumberFormatException e) { System.err.println("Argument must be an integer."); System.exit(1); } } threadMessage("Starting MessageLoop thread"); long startTime = System.currentTimeMillis(); Thread t = new Thread(new MessageLoop()); t.start(); threadMessage("Waiting for MessageLoop thread to finish"); //loop until MessageLoop thread exits while (t.isAlive()) { threadMessage("Still waiting..."); //Wait maximum of 1 second for MessageLoop thread to //finish. /*******LOOK HERE**********************/ Thread.sleep(1000);//issues caution unlike t.join(1000) /**************************************/ if (((System.currentTimeMillis() - startTime) > patience) && t.isAlive()) { threadMessage("Tired of waiting!"); t.interrupt(); //Shouldn't be long now -- wait indefinitely t.join(); } } threadMessage("Finally!"); } } As i understand it, join waits for the other thread to complete, but in this case, arent both sleep and join doing the same thing? Then why does netbeans throw the caution?

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• Python : How to close a UDP socket while is waiting for data in recv ?

  - by alexroat

  Hello, let's consider this code in python: import socket import threading import sys import select class UDPServer: def __init__(self): self.s=None self.t=None def start(self,port=8888): if not self.s: self.s=socket.socket(socket.AF_INET, socket.SOCK_DGRAM) self.s.bind(("",port)) self.t=threading.Thread(target=self.run) self.t.start() def stop(self): if self.s: self.s.close() self.t.join() self.t=None def run(self): while True: try: #receive data data,addr=self.s.recvfrom(1024) self.onPacket(addr,data) except: break self.s=None def onPacket(self,addr,data): print addr,data us=UDPServer() while True: sys.stdout.write("UDP server> ") cmd=sys.stdin.readline() if cmd=="start\n": print "starting server..." us.start(8888) print "done" elif cmd=="stop\n": print "stopping server..." us.stop() print "done" elif cmd=="quit\n": print "Quitting ..." us.stop() break; print "bye bye" It runs an interactive shell with which I can start and stop an UDP server. The server is implemented through a class which launches a thread in which there's a infinite loop of recv/*onPacket* callback inside a try/except block which should detect the error and the exits from the loop. What I expect is that when I type "stop" on the shell the socket is closed and an exception is raised by the recvfrom function because of the invalidation of the file descriptor. Instead, it seems that recvfrom still to block the thread waiting for data even after the close call. Why this strange behavior ? I've always used this patter to implements an UDP server in C++ and JAVA and it always worked. I've tried also with a "select" passing a list with the socket to the xread argument, in order to get an event of file descriptor disruption from select instead that from recvfrom, but select seems to be "insensible" to the close too. I need to have a unique code which maintain the same behavior on Linux and Windows with python 2.5 - 2.6. Thanks.

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• Queue access to the database to avoid multiple cache items

  - by MikeJ

  I have a music related ASP.NET web site which caches a lot of static information from the database on the first request. Sometimes, the application is reset and cache is cleared while the application is on heavy load and then all http requests go to the database to retrieve that static data and cache it for other requests. How can I ensure that only one request go to the database and cache the results, so that other request simply read that info from cache and not needlessly retrieve the same info over and over again. Can I use thread locking? For example, can I do something like lock(this) { db access here }?

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• How to wait for thread to finish with .NET?

  - by Maxim Z.

  I've never really used threading before in C# where I need to have two threads, as well as the main UI thread. Basically, I have the following. public void StartTheActions() { //Starting thread 1.... Thread t1 = new Thread(new ThreadStart(action1)); t1.Start(); //Now, I want for the main thread (which is calling StartTheActions() ) to wait for t1 to finish (I have created an event in action1() for this) and then start t2... //HOW DO I DO THIS? Thread t2 = new Thread(new ThreadStart(action2)); t2.Start(); } So, essentially, my question is how to have a thread wait for another one to finish. What is the best way to do this? Thanks!

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• Should I pass a SqlDataReader by reference or not when passing it out to multiple threads.

  - by deroby

  Hi all, being new to c# I've run into this 'conundrum' when passing around a SqlDataReader between different threads. Without going into too much detail, the idea is to have a main thread fetching data from the database (a large recordset) and then have a helper-task run through this record by record and doing some stuff based upon the contents of this. There is no feedback to the recordset, it simply wades through until no records are left. This works fine, but given the nature of the job at hand it should be possible to have this job spread over different threads (CPUs) to maximize throughput (the order of execution is of no significance). The question then becomes, when I pass this recordset in a SqlDataReader, do I have to use ref or not ? It kind of boils down to the question : if I pass the object around without specifying ref, won't it create new copies in memory and have records processed n times ? Or, don't I risk having the record-position being moved forward while not all fields have been fully read yet ? The latter seems more like a 'data racing' issue and probably is covered by the lock()ing mechanism (or not?). My initial take on the problem was that it doesn't really hurt passing the variable using ref, yet as a colleague put it : "you only need ref when you're doing something wrong" =) Additionally using ref restricts me from applying a Using() construction too which isn't very nice either. I thus create a "basic" project that tackles the same approach but without the ref notation. Tests so far show that it works flawlessly on a Core2Duo (2cpu) using any number of threads, yet I'm still a bit wary... What do you experts think about this ? Use ref or not ? You can find the test-project here as it seems I can't upload it to this question directly ?!? ps: it's just a test-project and I'm new to c#, so please be gentle on me when breaking down the code =P

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• embedding multiple lua instances in a multiple threaded program

  - by anon

  I have a program with 4 threads. Within each thread, I do a luaL_newstate(); Each thread only has access to it's own lua instance. Is there anything I need to worry about? [I.e. is there some hidden state that all lua instances share behind my back?] Thanks!

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• Efficiently display file status when using background thread

  - by schmoopy

  How can i efficiently display the status of a file when using a background thread? For instance, lets say i have a 100MB file: when i do the code below via a thread (just as an example) it runs in about 1 min: foreach(byte b in file.bytes) { WriteByte(b, xxx); } But... if i want to update the user i have to use a delegate to update the UI from the main thread, the code below takes - FOREVER - literally i don't know how long im still waiting, ive created this post and its not even 30% done. int total = file.length; int current = 0; foreach(byte b in file.bytes) { current++; UpdateCurrentFileStatus(current, total); WriteByte(b, xxx); } public delegate void UpdateCurrentFileStatus(int cur, int total); public void UpdateCurrentFileStatus(int cur, int total) { // Check if invoke required, if so create instance of delegate // the update the UI if(this.InvokeRequired) { } else { UpdateUI(...) } }

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• different thread accessing MemoryStream

  - by Wayne

  There's a bit of code which writes data to a MemoryStream object directly into it's data buffer by calling GetBuffer(). It also uses and updates the Position and SetLength() properties appropriately. This code works purposes 99.9999% of the time. Literally. Only every so many 100,000's of iterations it will barf. The specific problem is that the memory.Position property suddenly returns zero instead of the appropriate value. However, code was added that checks for the 0 and throws an exception which include log of the MemoryStream properties like Position and Length in a separate method. Those return the correct value. Further addition shows that when this rare condition occurs, the memory.Position only has zero inside this particular method. Okay. Obviously, this must be a threading issue. But this code is well locked. However, the nature of this software is that it's organized by "tasks" with a scheduler and so any one of several actual O/S thread may run this code at any give time--but never more than one at a time. So it's my guess that ordinarily it so happens that the same thread keeps getting used for this method and then on a rare occasion a different thread get used. Then due to compiler optimizations, the different thread never gets the correct value. It gets a "stale" value. Ordinarily in a situation like this I would apply a "volatile" keyword to the variable in question. But that (those) variables are inside the MemoryStream object. Does anyone have any other idea? Or does this mean we have to implement our own MemoryStream object? (Just like we end up having to do with practically every collection in .NET?) It's a shame to have such an awesome platform as .NET and have virtually the entire system useless as-is for seriously parallelized applications. If I'm wrong or you have other ideas, please advise. Sincerely, Wayne

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• Threads to make video out of images

  - by masood

  updates: I think/ suspect the imageIO is not thread safe. shared by all threads. the read() call might use resources that are also shared. Thus it will give the performance of a single thread no matter how many threads used. ? if its correct . what is the solution (in practical code) Single request and response model at one time do not utilizes full network/internet bandwidth, thus resulting in low performance. (benchmark is of half speed utilization or even lower) This is to make a video out of an IP cam that gives a new image on each request. http://149.5.43.10:8001/snapshot.jpg It makes a delay of 3 - 8 seconds no matter what I do. Changed thread no. and thread time intervals, debugged the code by System.out.println statements to see if threads work. All seems normal. Any help? Please show some practical code. You may modify mine. This code works (javascript) with much smoother frame rate and max bandwidth usage. but the later code (java) dont. same 3 to 8 seconds gap. <!DOCTYPE html> <html> <head> <script type="text/javascript"> (function(){ var img="/*url*/"; var interval=50; var pointer=0; function showImg(image,idx) { if(idx<=pointer) return; document.body.replaceChild(image,document.getElementsByTagName("img")[0]); pointer=idx; preload(); } function preload() { var cache=null,idx=0;; for(var i=0;i<5;i++) { idx=Date.now()+interval*(i+1); cache=new Image(); cache.onload=(function(ele,idx){return function(){showImg(ele,idx);};})(cache,idx); cache.src=img+"?"+idx; } } window.onload=function(){ document.getElementsByTagName("img")[0].onload=preload; document.getElementsByTagName("img")[0].src="/*initial url*/"; }; })(); </script> </head> <body> <img /> </body> </html> and of java (with problem) : package camba; import java.applet.Applet; import java.awt.Button; import java.awt.Graphics; import java.awt.Image; import java.awt.Label; import java.awt.Panel; import java.awt.TextField; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.net.URL; import java.security.Timestamp; import java.util.Date; import java.util.concurrent.TimeUnit; import java.util.concurrent.atomic.AtomicBoolean; import javax.imageio.ImageIO; public class Camba extends Applet implements ActionListener{ Image img; TextField textField; Label label; Button start,stop; boolean terminate = false; long viewTime; public void init(){ label = new Label("please enter camera URL "); add(label); textField = new TextField(30); add(textField); start = new Button("Start"); add(start); start.addActionListener(this); stop = new Button("Stop"); add(stop); stop.addActionListener(this); } public void actionPerformed(ActionEvent e){ Button source = (Button)e.getSource(); if(source.getLabel() == "Start"){ for (int i = 0; i < 7; i++) { myThread(50*i); } System.out.println("start..."); } if(source.getLabel() == "Stop"){ terminate = true; System.out.println("stop..."); } } public void paint(Graphics g) { update(g); } public void update(Graphics g){ try{ viewTime = System.currentTimeMillis(); g.drawImage(img, 100, 100, this); } catch(Exception e) { e.printStackTrace(); } } public void myThread(final int sleepTime){ new Thread(new Runnable() { public void run() { while(!terminate){ try { TimeUnit.MILLISECONDS.sleep(sleepTime); } catch (InterruptedException ex) { ex.printStackTrace(); } long requestTime= 0; Image tempImage = null; try { URL pic = null; requestTime= System.currentTimeMillis(); pic = new URL(getDocumentBase(), textField.getText()); tempImage = ImageIO.read(pic); } catch(Exception e) { e.printStackTrace(); } if(requestTime >= /*last view time*/viewTime){ img = tempImage; Camba.this.repaint(); } } }}).start(); System.out.println("thread started..."); } }

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• Pass a Message From Thread to Update UI

  - by Jay Dee

  Ive created a new thread for a file browser. The thread reads the contents of a directory. What I want to do is update the UI thread to draw a graphical representation of the files and folders. I know I can't update the UI from within a new thread so what I want to do is: whilst the file scanning thread iterates through a directories files and folders pass a file path string back to the UI thread. The handler in the UI thread then draws the graphical representation of the file passed back. public class New_Project extends Activity implements Runnable { private Handler handler = new Handler() { @Override public void handleMessage(Message msg) { Log.d("New Thread","Proccess Complete."); Intent intent = new Intent(); setResult(RESULT_OK, intent); finish(); } }; public void getFiles(){ //if (!XMLEFunctions.canReadExternal(this)) return; pd = ProgressDialog.show(this, "Reading Directory.", "Please Wait...", true, false); Log.d("New Thread","Called"); Thread thread = new Thread(this); thread.start(); } public void run() { Log.d("New Thread","Reading Files"); getFiles(); handler.sendEmptyMessage(0); } public void getFiles() { for (int i=0;i<=allFiles.length-1;i++){ //I WANT TO PASS THE FILE PATH BACK TU A HANDLER IN THE UI //SO IT CAN BE DRAWN. **passFilePathBackToBeDrawn(allFiles[i].toString());** } } }

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• Background thread in C#

  - by Xodarap

  When the user saves some data, I want to spin off a background thread to update my indexes and do some other random stuff. Even if there is an error in this indexing the user can't do anything about it, so there is no point in forcing the main thread to wait until the background thread finishes. I'm doing this from a ASP.NET process, so I think I should be able to do this (as the main thread exiting won't kill the process). When I set a breakpoint in the background thread's method though, the main thread also appears to stop. Is this just an artifact of visual studio's debugger, or is the main thread really not going to return until the background thread stops?

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• Best way to implement game loop without freezing UI thread

  - by Matt H

  I'm trying to make a simple 2D game in Java. So far I have a JFrame, with a menubar, and a class which extends JPanel and overrides it's paint method. Now, I need to get a game loop going, where I will update the position of images and so on. However, I'm stuck at how best to achieve this. Should I use multi-threading, because surely, if you put an infinite loop on the main thread, the UI (and thus my menu bar) will freeze up? Here's my code so far: import java.awt.Color; import java.awt.Graphics; import javax.swing.JPanel; @SuppressWarnings("serial") public class GameCanvas extends JPanel { public void paint(Graphics g) { while (true) { g.setColor(Color.DARK_GRAY); try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } } } } import javax.swing.JFrame; import javax.swing.JMenu; import javax.swing.JMenuBar; import javax.swing.JMenuItem; @SuppressWarnings("serial") public class Main extends JFrame { GameCanvas canvas = new GameCanvas(); final int FRAME_HEIGHT = 400; final int FRAME_WIDTH = 400; public static void main(String args[]) { new Main(); } public Main() { super("Game"); JMenuBar menuBar = new JMenuBar(); JMenu fileMenu = new JMenu("File"); JMenuItem startMenuItem = new JMenuItem("Pause"); menuBar.add(fileMenu); fileMenu.add(startMenuItem); super.add(canvas); super.setVisible(true); super.setSize(FRAME_WIDTH, FRAME_WIDTH); super.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); super.setJMenuBar(menuBar); } } Any pointers/tips? Also, where should I put my loop? In my main class, or my GameCanvas class? Any help is appreciated, thanks.

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• What Use are Threads Outside of Parallel Problems on MultiCore Systesm?

  - by Robert S. Barnes

  Threads make the design, implementation and debugging of a program significantly more difficult. Yet many people seem to think that every task in a program that can be threaded should be threaded, even on a single core system. I can understand threading something like an MPEG2 decoder that's going to run on a multicore cpu ( which I've done ), but what can justify the significant development costs threading entails when you're talking about a single core system or even a multicore system if your task doesn't gain significant performance from a parallel implementation? Or more succinctly, what kinds of non-performance related problems justify threading? Edit Well I just ran across one instance that's not CPU limited but threads make a big difference: TCP, HTTP and the Multi-Threading Sweet Spot Multiple threads are pretty useful when trying to max out your bandwidth to another peer over a high latency network connection. Non-blocking I/O would use significantly less local CPU resources, but would be much more difficult to design and implement.

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• How to build libpthread.so from source code?

  - by Tristan Su

  I need a non-stripped version of libpthread.so for debugging. How can I compile it from source code? Host is Linux 2.6.

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