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• PHP: Can pcntl_alarm() and socket_select() peacefully exist in the same thread?

  - by DWilliams

  I have a PHP CLI script mostly written that functions as a chat server for chat clients to connect to (don't ask me why I'm doing it in PHP, thats another story haha). My script utilizes the socket_select() function to hang execution until something happens on a socket, at which point it wakes up, processes the event, and waits until the next event. Now, there are some routine tasks that I need performed every 30 seconds or so (check of tempbanned users should be unbanned, save user databases, other assorted things). From what I can tell, PHP doesn't have very great multi-threading support at all. My first thought was to compare a timestamp every time the socket generates an event and gets the program flowing again, but this is very inconsistent since the server could very well sit idle for hours and not have any of my cleanup routines executed. I came across the PHP pcntl extensions, and it lets me use assign a time interval for SIGALRM to get sent and a function get executed every time it's sent. This seems like the ideal solution to my problem, however pcntl_alarm() and socket_select() clash with each other pretty bad. Every time SIGALRM is triggered, all sorts of crazy things happen to my socket control code. My program is fairly lengthy so I can't post it all here, but it shouldn't matter since I don't believe I'm doing anything wrong code-wise. My question is: Is there any way for a SIGALRM to be handled in the same thread as a waiting socket_select()? If so, how? If not, what are my alternatives here? Here's some output from my program. My alarm function simply outputs "Tick!" whenever it's called to make it easy to tell when stuff is happening. This is the output (including errors) after allowing it to tick 4 times (there were no actual attempts at connecting to the server despite what it says): [05-28-10 @ 20:01:05] Chat server started on 192.168.1.28 port 4050 [05-28-10 @ 20:01:05] Loaded 2 users from file PHP Notice: Undefined offset: 0 in /home/danny/projects/PHPChatServ/ChatServ.php on line 112 PHP Warning: socket_select(): unable to select [4]: Interrupted system call in /home/danny/projects/PHPChatServ/ChatServ.php on line 116 [05-28-10 @ 20:01:15] Tick! PHP Warning: socket_accept(): unable to accept incoming connection [4]: Interrupted system call in /home/danny/projects/PHPChatServ/ChatServ.php on line 126 [05-28-10 @ 20:01:25] Tick! PHP Warning: socket_getpeername() expects parameter 1 to be resource, boolean given in /home/danny/projects/PHPChatServ/ChatServ.php on line 129 [05-28-10 @ 20:01:25] Accepting socket connection from PHP Notice: Undefined offset: 1 in /home/danny/projects/PHPChatServ/ChatServ.php on line 112 PHP Warning: socket_select(): unable to select [4]: Interrupted system call in /home/danny/projects/PHPChatServ/ChatServ.php on line 116 [05-28-10 @ 20:01:35] Tick! PHP Warning: socket_accept(): unable to accept incoming connection [4]: Interrupted system call in /home/danny/projects/PHPChatServ/ChatServ.php on line 126 [05-28-10 @ 20:01:45] Tick! PHP Warning: socket_getpeername() expects parameter 1 to be resource, boolean given in /home/danny/projects/PHPChatServ/ChatServ.php on line 129 [05-28-10 @ 20:01:45] Accepting socket connection from PHP Notice: Undefined offset: 2 in /home/danny/projects/PHPChatServ/ChatServ.php on line 112

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• Does oneway declaration in Android .aidl guarantee that method will be called in a separate thread?

  - by Dan Menes

  I am designing a framework for a client/server application for Android phones. I am fairly new to both Java and Android (but not new to programming in general, or threaded programming in particular). Sometimes my server and client will be in the same process, and sometimes they will be in different processes, depending on the exact use case. The client and server interfaces look something like the following: IServer.aidl: package com.my.application; interface IServer { /** * Register client callback object */ void registerCallback( in IClient callbackObject ); /** * Do something and report back */ void doSomething( in String what ); . . . } IClient.aidl: package com.my.application; oneway interface IClient { /** * Receive an answer */ void reportBack( in String answer ); . . . } Now here is where it gets interesting. I can foresee use cases where the client calls IServer.doSomething(), which in turn calls IClient.reportBack(), and on the basis of what is reported back, IClient.reportBack() needs to issue another call to IClient.doSomething(). The issue here is that IServer.doSomething() will not, in general, be reentrant. That's OK, as long as IClient.reportBack() is always invoked in a new thread. In that case, I can make sure that the implementation of IServer.doSomething() is always synchronized appropriately so that the call from the new thread blocks until the first call returns. If everything works the way I think it does, then by declaring the IClient interface as oneway, I guarantee this to be the case. At least, I can't think of any way that the call from IServer.doSomething() to IClient.reportBack() can return immediately (what oneway is supposed to ensure), yet IClient.reportBack still be able to reinvoke IServer.doSomething recursively in the same thread. Either a new thread in IServer must be started, or else the old IServer thread can be re-used for the inner call to IServer.doSomething(), but only after the outer call to IServer.doSomething() has returned. So my question is, does everything work the way I think it does? The Android documentation hardly mentions oneway interfaces.

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• Why does ffmpeg stop randomly in the middle of a process?

  - by acidzombie24

  ffmpeg feels like its taking a long time. I then look at my output file and i see it stops between 6 and 8mbs. A fully encoded file is about 14mb. Why does ffmpeg stop? My code locks up on StandardOutput.ReadToEnd();. I had to kill the process (after seeing it not move for more then 10 seconds when i see it update every second previously) then i get the results of stdout and err. stdout is "" stderr is below. The output msg shows the filesize ended. I also see a drop in my CPU usage when it stops. I copyed the argument from visual studios. CD to the same working directory and ran the cmd (bin/ffmpeg) and pasted the argument. It was able to complete. int soundProcess(string infn, string outfn) { string aa, aa2; aa = aa2 = "DEAD"; var app = new Process(); app.StartInfo.UseShellExecute = false; app.StartInfo.RedirectStandardOutput = true; app.StartInfo.RedirectStandardError = true; //*/ app.StartInfo.FileName = @"bin\ffmpeg.exe"; app.StartInfo.Arguments = string.Format(@"-i ""{0}"" -ab 192k -y {2} ""{1}""", infn, outfn, param); app.Start(); try { app.PriorityClass = ProcessPriorityClass.BelowNormal; } catch (Exception ex) { if (!Regex.IsMatch(ex.Message, @"Cannot process request because the process .*has exited")) throw ex; } aa = app.StandardOutput.ReadToEnd(); aa2 = app.StandardError.ReadToEnd(); app.WaitForExit(); if (aa2.IndexOf("could not find codec parameters") != -1) return 1; else if (aa == "DEAD" || aa2 == "DEAD") return -1; else if (aa2.Length != 0) return -2; else return 0; } The output of stderr. stdout is empty. FFmpeg version SVN-r15815, Copyright (c) 2000-2008 Fabrice Bellard, et al. configuration: --enable-memalign-hack --enable-postproc --enable-swscale --enable-gpl --enable-libfaac --enable-libfaad --enable-libgsm --enable-libmp3lame --enable-libvorbis --enable-libtheora --enable-libx264 --enable-libxvid --disable-ffserver --disable-vhook --enable-avisynth --enable-pthreads libavutil 49.12. 0 / 49.12. 0 libavcodec 52. 3. 0 / 52. 3. 0 libavformat 52.23. 1 / 52.23. 1 libavdevice 52. 1. 0 / 52. 1. 0 libswscale 0. 6. 1 / 0. 6. 1 libpostproc 51. 2. 0 / 51. 2. 0 built on Nov 13 2008 10:28:29, gcc: 4.2.4 (TDM-1 for MinGW) Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'C:\dev\src\trunk\prjname\prjname\App_Data/temp/m/o/6304266424778814852': Duration: 00:12:53.36, start: 0.000000, bitrate: 154 kb/s Stream #0.0(und): Audio: aac, 44100 Hz, stereo, s16 Output #0, ipod, to 'C:\dev\src\trunk\prjname\prjname\App_Data\temp\m\o\2.m4a': Stream #0.0(und): Audio: libfaac, 44100 Hz, stereo, s16, 192 kb/s Stream mapping: Stream #0.0 -> #0.0 Press [q] to stop encoding size= 87kB time=4.74 bitrate= 150.7kbits/s size= 168kB time=9.06 bitrate= 151.9kbits/s size= 265kB time=14.28 bitrate= 151.8kbits/s size= 377kB time=20.29 bitrate= 152.1kbits/s size= 487kB time=26.22 bitrate= 152.1kbits/s size= 594kB time=32.02 bitrate= 152.1kbits/s size= 699kB time=37.64 bitrate= 152.1kbits/s size= 808kB time=43.54 bitrate= 152.0kbits/s size= 930kB time=50.09 bitrate= 152.2kbits/s size= 1058kB time=57.05 bitrate= 152.0kbits/s size= 1193kB time=64.23 bitrate= 152.1kbits/s size= 1329kB time=71.63 bitrate= 152.0kbits/s size= 1450kB time=78.16 bitrate= 152.0kbits/s size= 1578kB time=85.05 bitrate= 152.0kbits/s size= 1706kB time=92.00 bitrate= 152.0kbits/s size= 1836kB time=98.94 bitrate= 152.0kbits/s size= 1971kB time=106.25 bitrate= 151.9kbits/s size= 2107kB time=113.57 bitrate= 152.0kbits/s size= 2214kB time=119.33 bitrate= 152.0kbits/s size= 2345kB time=126.39 bitrate= 152.0kbits/s size= 2479kB time=133.56 bitrate= 152.0kbits/s size= 2611kB time=140.76 bitrate= 152.0kbits/s size= 2745kB time=147.91 bitrate= 152.1kbits/s size= 2880kB time=155.20 bitrate= 152.0kbits/s size= 3013kB time=162.40 bitrate= 152.0kbits/s size= 3146kB time=169.58 bitrate= 152.0kbits/s size= 3277kB time=176.61 bitrate= 152.0kbits/s size= 3412kB time=183.90 bitrate= 152.0kbits/s size= 3540kB time=190.80 bitrate= 152.0kbits/s size= 3670kB time=197.81 bitrate= 152.0kbits/s size= 3805kB time=205.08 bitrate= 152.0kbits/s size= 3932kB time=211.93 bitrate= 152.0kbits/s size= 4052kB time=218.38 bitrate= 152.0kbits/s size= 4171kB time=224.82 bitrate= 152.0kbits/s size= 4277kB time=230.55 bitrate= 152.0kbits/s size= 4378kB time=235.96 bitrate= 152.0kbits/s size= 4486kB time=241.79 bitrate= 152.0kbits/s size= 4592kB time=247.50 bitrate= 152.0kbits/s size= 4698kB time=253.21 bitrate= 152.0kbits/s size= 4804kB time=258.95 bitrate= 152.0kbits/s size= 4906kB time=264.41 bitrate= 152.0kbits/s size= 5012kB time=270.09 bitrate= 152.0kbits/s size= 5118kB time=275.85 bitrate= 152.0kbits/s size= 5234kB time=282.10 bitrate= 152.0kbits/s size= 5331kB time=287.39 bitrate= 151.9kbits/s size= 5445kB time=293.55 bitrate= 152.0kbits/s size= 5555kB time=299.40 bitrate= 152.0kbits/s size= 5665kB time=305.37 bitrate= 152.0kbits/s size= 5766kB time=310.80 bitrate= 152.0kbits/s size= 5876kB time=316.70 bitrate= 152.0kbits/s size= 5984kB time=322.50 bitrate= 152.0kbits/s size= 6094kB time=328.49 bitrate= 152.0kbits/s size= 6212kB time=334.76 bitrate= 152.0kbits/s size= 6327kB time=340.99 bitrate= 152.0kbits/s

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• Asynchronous subprocess on Windows

  - by Stigma

  First of all, the overall problem I am solving is a bit more complicated than I am showing here, so please do not tell me 'use threads with blocking' as it would not solve my actual situation without a fair, FAIR bit of rewriting and refactoring. I have several applications which are not mine to modify, which take data from stdin and poop it out on stdout after doing their magic. My task is to chain several of these programs. Problem is, sometimes they choke, and as such I need to track their progress which is outputted on STDERR. pA = subprocess.Popen(CommandA, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE) # ... some more processes make up the chain, but that is irrelevant to the problem pB = subprocess.Popen(CommandB, shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=pA.stdout ) Now, reading directly through pA.stdout.readline() and pB.stdout.readline(), or the plain read() functions, is a blocking matter. Since different applications output in different paces and different formats, blocking is not an option. (And as I wrote above, threading is not an option unless at a last, last resort.) pA.communicate() is deadlock safe, but since I need the information live, that is not an option either. Thus google brought me to this asynchronous subprocess snippet on ActiveState. All good at first, until I implement it. Comparing the cmd.exe output of pA.exe | pB.exe, ignoring the fact both output to the same window making for a mess, I see very instantaneous updates. However, I implement the same thing using the above snippet and the read_some() function declared there, and it takes over 10 seconds to notify updates of a single pipe. But when it does, it has updates leading all the way upto 40% progress, for example. Thus I do some more research, and see numerous subjects concerning PeekNamedPipe, anonymous handles, and returning 0 bytes available even though there is information available in the pipe. As the subject has proven quite a bit beyond my expertise to fix or code around, I come to Stack Overflow to look for guidance. :) My platform is W7 64-bit with Python 2.6, the applications are 32-bit in case it matters, and compatibility with Unix is not a concern. I can even deal with a full ctypes or pywin32 solution that subverts subprocess entirely if it is the only solution, as long as I can read from every stderr pipe asynchronously with immediate performance and no deadlocks. :)

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• Problems doing asynch operations in C# using Mutex.

  - by firoso

  I've tried this MANY ways, here is the current iteration. I think I've just implemented this all wrong. What I'm trying to accomplish is to treat this Asynch result in such a way that until it returns AND I finish with my add-thumbnail call, I will not request another call to imageProvider.BeginGetImage. To Clarify, my question is two-fold. Why does what I'm doing never seem to halt at my Mutex.WaitOne() call, and what is the proper way to handle this scenario? /// <summary> /// re-creates a list of thumbnails from a list of TreeElementViewModels (directories) /// </summary> /// <param name="list">the list of TreeElementViewModels to process</param> public void BeginLayout(List<AiTreeElementViewModel> list) { // *removed code for canceling and cleanup from previous calls* // Starts the processing of all folders in parallel. Task.Factory.StartNew(() => { thumbnailRequests = Parallel.ForEach<AiTreeElementViewModel>(list, options, ProcessFolder); }); } /// <summary> /// Processes a folder for all of it's image paths and loads them from disk. /// </summary> /// <param name="element">the tree element to process</param> private void ProcessFolder(AiTreeElementViewModel element) { try { var images = ImageCrawler.GetImagePaths(element.Path); AsyncCallback callback = AddThumbnail; foreach (var image in images) { Console.WriteLine("Attempting Enter"); synchMutex.WaitOne(); Console.WriteLine("Entered"); var result = imageProvider.BeginGetImage(callback, image); } } catch (Exception exc) { Console.WriteLine(exc.ToString()); // TODO: Do Something here. } } /// <summary> /// Adds a thumbnail to the Browser /// </summary> /// <param name="result">an async result used for retrieving state data from the load task.</param> private void AddThumbnail(IAsyncResult result) { lock (Thumbnails) { try { Stream image = imageProvider.EndGetImage(result); string filename = imageProvider.GetImageName(result); string imagePath = imageProvider.GetImagePath(result); var imageviewmodel = new AiImageThumbnailViewModel(image, filename, imagePath); thumbnailHash[imagePath] = imageviewmodel; HostInvoke(() => Thumbnails.Add(imageviewmodel)); UpdateChildZoom(); //synchMutex.ReleaseMutex(); Console.WriteLine("Exited"); } catch (Exception exc) { Console.WriteLine(exc.ToString()); // TODO: Do Something here. } } }

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• Hung JVM consuming 100% CPU

  - by Bogdan

  We have a JAVA server running on Sun JRE 6u20 on Linux 32-bit (CentOS). We use the Server Hotspot with CMS collector with the following options (I've only provided the relevant ones): -Xmx896m -Xss128k -XX:NewSize=384M -XX:MaxPermSize=96m -XX:+UseParNewGC -XX:+UseConcMarkSweepGC Sometimes, after running for a while, the JVM seems to slip into a hung state, whereby even though we don't make any requests to the application, the CPU continues to spin at 100% (we have 8 logical CPUs, so it looks like only one CPU does the spinning). In this state the JVM doesn't respond to SIGHUP signals (kill -3) and we can't connect to it normally with jstack. We CAN connect with "jstack -F", but the output is dodgy (we can see lots of NullPointerExceptions from JStack apparently because it wasn't able to 'walk' some stacks). So the "jstack -F" output seems to be useless. We have run a stack dump from "gdb" though, and we were able to match the thread id that spins the CPU (we found that using "top" with a per-thread view - "H" option) with a thread stack that appears in the gdb result and this is how it looks like: Thread 443 (Thread 0x7e5b90 (LWP 26310)): #0 0x0115ebd3 in CompactibleFreeListSpace::block_size(HeapWord const*) const () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #1 0x01160ff9 in CompactibleFreeListSpace::prepare_for_compaction(CompactPoint*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #2 0x0123456c in Generation::prepare_for_compaction(CompactPoint*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #3 0x01229b2c in GenCollectedHeap::prepare_for_compaction() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #4 0x0122a7fc in GenMarkSweep::invoke_at_safepoint(int, ReferenceProcessor*, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #5 0x01186024 in CMSCollector::do_compaction_work(bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #6 0x011859ee in CMSCollector::acquire_control_and_collect(bool, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #7 0x01185705 in ConcurrentMarkSweepGeneration::collect(bool, bool, unsigned int, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #8 0x01227f53 in GenCollectedHeap::do_collection(bool, bool, unsigned int, bool, int) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #9 0x0115c7b5 in GenCollectorPolicy::satisfy_failed_allocation(unsigned int, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #10 0x0122859c in GenCollectedHeap::satisfy_failed_allocation(unsigned int, bool) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #11 0x0158a8ce in VM_GenCollectForAllocation::doit() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #12 0x015987e6 in VM_Operation::evaluate() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #13 0x01597c93 in VMThread::evaluate_operation(VM_Operation*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #14 0x01597f0f in VMThread::loop() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #15 0x015979f0 in VMThread::run() () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #16 0x0145c24e in java_start(Thread*) () from /usr/java/jdk1.6.0_20/jre/lib/i386/server/libjvm.so #17 0x00ccd46b in start_thread () from /lib/libpthread.so.0 #18 0x00bc2dbe in clone () from /lib/libc.so.6 It seems that a JVM thread is spinning while doing some CMS related work. We have checked the memory usage on the box, there seems to be enough memory available and the system is not swapping. Has anyone come across such a situation? Does it look like a JVM bug? UPDATE I've obtained some more information about this problem (it happened again on a server that has been running for more than 7 days). When the JVM entered the "hung" state it stayed like that for 2 hours until the server was manually restarted. We have obtained a core dump of the process and the gc log. We tried to get a heap dump as well, but "jmap" failed. We tried to use jmap -F but then only a 4Mb file was written before the program aborted with an exception (something about the a memory location not being accessible). So far I think the most interesting information comes from the gc log. It seems that the GC logging stopped as well (possibly at the time when the VM thread went into the long loop): 657501.199: [Full GC (System) 657501.199: [CMS: 400352K->313412K(524288K), 2.4024120 secs] 660634K->313412K(878208K), [CMS Perm : 29455K->29320K(68568K)], 2.4026470 secs] [Times: user=2.39 sys=0.01, real=2.40 secs] 657513.941: [GC 657513.941: [ParNew: 314624K->13999K(353920K), 0.0228180 secs] 628036K->327412K(878208K), 0.0230510 secs] [Times: user=0.08 sys=0.00, real=0.02 secs] 657523.772: [GC 657523.772: [ParNew: 328623K->17110K(353920K), 0.0244910 secs] 642036K->330523K(878208K), 0.0247140 secs] [Times: user=0.08 sys=0.00, real=0.02 secs] 657535.473: [GC 657535.473: [ParNew: 331734K->20282K(353920K), 0.0259480 secs] 645147K->333695K(878208K), 0.0261670 secs] [Times: user=0.11 sys=0.00, real=0.02 secs] .... .... 688346.765: [GC [1 CMS-initial-mark: 485248K(524288K)] 515694K(878208K), 0.0343730 secs] [Times: user=0.03 sys=0.00, real=0.04 secs] 688346.800: [CMS-concurrent-mark-start] 688347.964: [CMS-concurrent-mark: 1.083/1.164 secs] [Times: user=2.52 sys=0.09, real=1.16 secs] 688347.964: [CMS-concurrent-preclean-start] 688347.969: [CMS-concurrent-preclean: 0.004/0.005 secs] [Times: user=0.00 sys=0.01, real=0.01 secs] 688347.969: [CMS-concurrent-abortable-preclean-start] CMS: abort preclean due to time 688352.986: [CMS-concurrent-abortable-preclean: 2.351/5.017 secs] [Times: user=3.83 sys=0.38, real=5.01 secs] 688352.987: [GC[YG occupancy: 297806 K (353920 K)]688352.987: [Rescan (parallel) , 0.1815250 secs]688353.169: [weak refs processing, 0.0312660 secs] [1 CMS-remark: 485248K(524288K)] 783055K(878208K), 0.2131580 secs] [Times: user=1.13 sys =0.00, real=0.22 secs] 688353.201: [CMS-concurrent-sweep-start] 688353.903: [CMS-concurrent-sweep: 0.660/0.702 secs] [Times: user=0.91 sys=0.07, real=0.70 secs] 688353.903: [CMS-concurrent-reset-start] 688353.912: [CMS-concurrent-reset: 0.008/0.008 secs] [Times: user=0.01 sys=0.00, real=0.01 secs] 688354.243: [GC 688354.243: [ParNew: 344928K->30151K(353920K), 0.0305020 secs] 681955K->368044K(878208K), 0.0308880 secs] [Times: user=0.15 sys=0.00, real=0.03 secs] .... .... 688943.029: [GC 688943.029: [ParNew: 336531K->17143K(353920K), 0.0237360 secs] 813250K->494327K(878208K), 0.0241260 secs] [Times: user=0.10 sys=0.00, real=0.03 secs] 688950.620: [GC 688950.620: [ParNew: 331767K->22442K(353920K), 0.0344110 secs] 808951K->499996K(878208K), 0.0347690 secs] [Times: user=0.11 sys=0.00, real=0.04 secs] 688956.596: [GC 688956.596: [ParNew: 337064K->37809K(353920K), 0.0488170 secs] 814618K->515896K(878208K), 0.0491550 secs] [Times: user=0.18 sys=0.04, real=0.05 secs] 688961.470: [GC 688961.471: [ParNew (promotion failed): 352433K->332183K(353920K), 0.1862520 secs]688961.657: [CMS I suspect this problem has something to do with the last line in the log (I've added some "...." in order to skip some lines that were not interesting). The fact that the server stayed in the hung state for 2 hours (probably trying to GC and compact the old generation) seems quite strange to me. Also, the gc log stops suddenly with that message and nothing else gets printed any more, probably because the VM Thread gets into some sort of infinite loop (or something that takes 2+ hours).

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• Erasing and modifying elements in Boost MultiIndex Container

  - by Sarah

  I'm trying to use a Boost MultiIndex container in my simulation. My knowledge of C++ syntax is very weak, and I'm concerned I'm not properly removing an element from the container or deleting it from memory. I also need to modify elements, and I was hoping to confirm the syntax and basic philosophy here too. // main.cpp ... #include <boost/multi_index_container.hpp> #include <boost/multi_index/hashed_index.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/mem_fun.hpp> #include <boost/tokenizer.hpp> #include <boost/shared_ptr.hpp> ... #include "Host.h" // class Host, all members private, using get fxns to access using boost::multi_index_container; using namespace boost::multi_index; typedef multi_index_container< boost::shared_ptr< Host >, indexed_by< hashed_unique< const_mem_fun<Host,int,&Host::getID> > // ordered_non_unique< BOOST_MULTI_INDEX_MEM_FUN(Host,int,&Host::getAge) > > // end indexed_by > HostContainer; typedef HostContainer::nth_index<0>::type HostsByID; int main() { ... HostContainer allHosts; Host * newHostPtr; newHostPtr = new Host( t, DOB, idCtr, 0, currentEvents ); allHosts.insert( boost::shared_ptr<Host>(newHostPtr) ); // allHosts gets filled up int randomHostID = 4; int newAge = 50; modifyHost( randomHostID, allHosts, newAge ); killHost( randomHostID, allHosts ); } void killHost( int id, HostContainer & hmap ){ HostsByID::iterator it = hmap.find( id ); cout << "Found host id " << (*it)->getID() << "Attempting to kill. hmap.size() before is " << hmap.size() << " and "; hmap.erase( it ); // Is this really erasing (freeing from mem) the underlying Host object? cout << hmap.size() << " after." << endl; } void modifyHost( int id, HostContainer & hmap, int newAge ){ HostsByID::iterator it = hmap.find( id ); (*it) -> setAge( newAge ); // Not actually the "modify" function for MultiIndex... } My questions are In the MultiIndex container allHosts of shared_ptrs to Host objects, is calling allHosts.erase( it ) on an iterator to the object's shared_ptr enough to delete the object permanently and free it from memory? It appears to be removing the shared_ptr from the container. The allhosts container currently has one functioning index that relies on the host's ID. If I introduce an ordered second index that calls on a member function (Host::getAge()), where the age changes over the course of the simulation, is the index always going to be updated when I refer to it? What is the difference between using the MultiIndex's modify to modify the age of the underlying object versus the approach I show above? I'm vaguely confused about what is assumed/required to be constant in MultiIndex. Thanks in advance. Update Here's my attempt to get the modify syntax working, based on what I see in a related Boost example. struct update_age { update_age():(){} // have no idea what this really does... elicits error void operator() (boost::shared_ptr<Host> ptr) { ptr->incrementAge(); // incrementAge() is a member function of class Host } }; and then in modifyHost, I'd have hmap.modify(it,update_age). Even if by some miracle this turns out to be right, I'd love some kind of explanation of what's going on.

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• LINQ InsertOnSubmit Required Fields needed for debugging

  - by Derek Hunziker

  Hi All, I've been using the ADO.NET Strogly-Typed DataSet model for about 2 years now for handling CRUD and stored procedure executions. This past year I built my first MVC app and I really enjoyed the ease and flexibility of LINQ. Perhaps the biggest selling point for me was that with LINQ I didn't have to create "Insert" stored procedures that would return the SCOPE_IDENTITY anymore (The auto-generated insert statements in the DataSet model were not capable of this without modification). Currently, I'm using LINQ with ASP.NET 3.5 WebForms. My inserts are looking like this: ProductsDataContext dc = new ProductsDataContext(); product p = new product { Title = "New Product", Price = 59.99, Archived = false }; dc.products.InsertOnSubmit(p); dc.SubmitChanges(); int productId = p.Id; So, this product example is pretty basic, right, and in the future, I'll probably be adding more fields to the database such as "InStock", "Quantity", etc... The way I understand it, I will need to add those fields to the database table and then delete and re-add the tables to the LINQ to SQL Class design view in order to refresh the DataContext. Does that sound right? The problem is that any new fields that are non-null are NOT caught by the ASP.NET build processes. For example, if I added a non-null field of "Quantity" to the database, the code above would still build. In the DataSet model, the stored procedure method would accept a certain amount of parameters and would warn me that my Insert would fail if I didn't include a quantity value. The same goes for LINQ stored procedure methods, however, to my knowledge, LINQ doesn't offer a way to auto generate the insert statements and that means I'm back to where I started. The bottom line is if I used insert statements like the one above and I add a non-null field to my database, it would break my app in about 10-20 places and there would be no way for me to detect it. Is my only option to do a solution-side search for the keyword "products.InsertOnSubmit" and make sure the new field is getting assigned? Is there a better way? Thanks!

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• Keeping files or database records? Java and Python

  - by danpalmer

  My website will use a Neural Network to predict thing based on user data. The user can select the data to be used in training the network and then use their trained network to predict things. I am using a framework to create, train and query the networks. This uses Java. The framework has persistence for saving a network to an XML file. What is the best way to store these files? I can see several potential ideas, but I need help on choosing which is best: Save each network to a separate XML file with a name that is stored in the database. Load this each time. Save all the networks to the same XML file with each network having a different name that is stored in the database. Somehow pass what would normally be written to an XML file to the Django site for writing to the database. This would need to be returned to the Java code when a prediction needs to be made. I am able to do 1 or 2, but I think their performance will be quite limited and I am on shared hosting at the moment, so I don't know how pleased they would be with thousands of files. Also, after adding a few thousand records to one XML file, I was noticing a massive performance hit on saving to it. If I were able to implement version 3 somehow I think it would be best. No issues with separate processes accessing the database and I think performance would be better. Not to mention having no files lying around. However, the stuff in the neural network framework I am using (Encog) for saving to a file needs access to a Java file object, not a string that could be saved to a database. Unless there is some Java magic I can do here (I know very little Java), the only way I can see of doing this would be with a temporary files but I don't know if this is the correct way to do it. I would appreciate any ideas on the best way to implement any of the above 3 ideas or any alternatives. Thanks!

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• Why does one loop take longer to detect a shared memory update than another loop?

  - by Joseph Garvin

  I've written a 'server' program that writes to shared memory, and a client program that reads from the memory. The server has different 'channels' that it can be writing to, which are just different linked lists that it's appending items too. The client is interested in some of the linked lists, and wants to read every node that's added to those lists as it comes in, with the minimum latency possible. I have 2 approaches for the client: For each linked list, the client keeps a 'bookmark' pointer to keep its place within the linked list. It round robins the linked lists, iterating through all of them over and over (it loops forever), moving each bookmark one node forward each time if it can. Whether it can is determined by the value of a 'next' member of the node. If it's non-null, then jumping to the next node is safe (the server switches it from null to non-null atomically). This approach works OK, but if there are a lot of lists to iterate over, and only a few of them are receiving updates, the latency gets bad. The server gives each list a unique ID. Each time the server appends an item to a list, it also appends the ID number of the list to a master 'update list'. The client only keeps one bookmark, a bookmark into the update list. It endlessly checks if the bookmark's next pointer is non-null ( while(node->next_ == NULL) {} ), if so moves ahead, reads the ID given, and then processes the new node on the linked list that has that ID. This, in theory, should handle large numbers of lists much better, because the client doesn't have to iterate over all of them each time. When I benchmarked the latency of both approaches (using gettimeofday), to my surprise #2 was terrible. The first approach, for a small number of linked lists, would often be under 20us of latency. The second approach would have small spats of low latencies but often be between 4,000-7,000us! Through inserting gettimeofday's here and there, I've determined that all of the added latency in approach #2 is spent in the loop repeatedly checking if the next pointer is non-null. This is puzzling to me; it's as if the change in one process is taking longer to 'publish' to the second process with the second approach. I assume there's some sort of cache interaction going on I don't understand. What's going on?

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• I need help with Widget and PendingIntents

  - by YaW

  Hi, I've asked here a question about Task Killers and widgets stop working (SO Question) but now, I have reports of user that they don't use any Task Killer and the widgets didn't work after a while. I have a Nexus One and I don't have this problem. I don't know if this is a problem of memory or something. Based on the API: A PendingIntent itself is simply a reference to a token maintained by the system describing the original data used to retrieve it. This means that, even if its owning application's process is killed, the PendingIntent itself will remain usable from other processes that have been given it. So, I don't know why widget stop working, if Android doesn't kill the PendingIntent by itself, what's the problem? This is my manifest code: <receiver android:name=".widget.InstantWidget" android:label="@string/app_name"> <intent-filter> <action android:name="android.appwidget.action.APPWIDGET_UPDATE" /> </intent-filter> <meta-data android:name="android.appwidget.provider" android:resource="@xml/widget_provider" /> </receiver> And the widget code: public class InstantWidget extends AppWidgetProvider { public static ArrayList<Integer> alWidgetsId = new ArrayList<Integer>(); private static final String PREFS_NAME = "com.cremagames.instant.InstantWidget"; private static final String PREF_PREFIX_NOM = "nom_"; private static final String PREF_PREFIX_RAW = "raw_"; /** * Esto se llama cuando se crea el widget. Metemos en las preferencias los valores de nombre y raw para tenerlos en proximos reboot. * @param context * @param appWidgetManager * @param appWidgetId * @param nombreSound * @param rawSound */ static void updateAppWidget(Context context, AppWidgetManager appWidgetManager, int appWidgetId, String nombreSound, int rawSound){ //Guardamos en las prefs los valores SharedPreferences.Editor prefs = context.getSharedPreferences(PREFS_NAME, 0).edit(); prefs.putString(PREF_PREFIX_NOM + appWidgetId, nombreSound); prefs.putInt(PREF_PREFIX_RAW + appWidgetId, rawSound); prefs.commit(); //Actualizamos la interfaz updateWidgetGrafico(context, appWidgetManager, appWidgetId, nombreSound, rawSound); } /** * Actualiza la interfaz gráfica del widget (pone el nombre y crea el intent con el raw) * @param context * @param appWidgetManager * @param appWidgetId * @param nombreSound * @param rawSound */ private static void updateWidgetGrafico(Context context, AppWidgetManager appWidgetManager, int appWidgetId, String nombreSound, int rawSound){ RemoteViews remoteViews = new RemoteViews(context.getPackageName(), R.layout.widget); //Nombre del Button remoteViews.setTextViewText(R.id.tvWidget, nombreSound); //Creamos el PendingIntent para el onclik del boton Intent active = new Intent(context, InstantWidget.class); active.setAction(String.valueOf(appWidgetId)); active.putExtra("sonido", rawSound); PendingIntent actionPendingIntent = PendingIntent.getBroadcast(context, 0, active, 0); actionPendingIntent.cancel(); actionPendingIntent = PendingIntent.getBroadcast(context, 0, active, 0); remoteViews.setOnClickPendingIntent(R.id.btWidget, actionPendingIntent); appWidgetManager.updateAppWidget(appWidgetId, remoteViews); } public void onReceive(Context context, Intent intent) { final String action = intent.getAction(); //Esto se usa en la 1.5 para que se borre bien el widget if (AppWidgetManager.ACTION_APPWIDGET_DELETED.equals(action)) { final int appWidgetId = intent.getExtras().getInt( AppWidgetManager.EXTRA_APPWIDGET_ID, AppWidgetManager.INVALID_APPWIDGET_ID); if (appWidgetId != AppWidgetManager.INVALID_APPWIDGET_ID) { this.onDeleted(context, new int[] { appWidgetId }); } } else { //Listener de los botones for(int i=0; i<alWidgetsId.size(); i++){ if (intent.getAction().equals(String.valueOf(alWidgetsId.get(i)))) { int sonidoRaw = 0; try { sonidoRaw = intent.getIntExtra("sonido", 0); } catch (NullPointerException e) { } MediaPlayer mp = MediaPlayer.create(context, sonidoRaw); mp.start(); mp.setOnCompletionListener(completionListener); } } super.onReceive(context, intent); } } /** Al borrar el widget, borramos también las preferencias **/ public void onDeleted(Context context, int[] appWidgetIds) { for(int i=0; i<appWidgetIds.length; i++){ //Recogemos las preferencias SharedPreferences.Editor prefs = context.getSharedPreferences(PREFS_NAME, 0).edit(); prefs.remove(PREF_PREFIX_NOM + appWidgetIds[i]); prefs.remove(PREF_PREFIX_RAW + appWidgetIds[i]); prefs.commit(); } super.onDeleted(context, appWidgetIds); } /**Este método se llama cada vez que se refresca un widget. En nuestro caso, al crearse y al reboot del telefono. Al crearse lo único que hace es guardar el id en el arrayList Al reboot, vienen varios ID así que los recorremos y guardamos todos y también recuperamos de las preferencias el nombre y el sonido*/ public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) { for(int i=0; i<appWidgetIds.length; i++){ //Metemos en el array los IDs de los widgets alWidgetsId.add(appWidgetIds[i]); //Recogemos las preferencias SharedPreferences prefs = context.getSharedPreferences(PREFS_NAME, 0); String nomSound = prefs.getString(PREF_PREFIX_NOM + appWidgetIds[i], null); int rawSound = prefs.getInt(PREF_PREFIX_RAW + appWidgetIds[i], 0); //Si están creadas, actualizamos la interfaz if(nomSound != null){ updateWidgetGrafico(context, appWidgetManager, appWidgetIds[i], nomSound, rawSound); } } } MediaPlayer.OnCompletionListener completionListener = new MediaPlayer.OnCompletionListener(){ public void onCompletion(MediaPlayer mp) { if(mp != null){ mp.stop(); mp.release(); mp = null; } } }; } Sorry for the comments in Spanish. I have the possibility to put differents widgets on the desktop, that's why I use the widgetId as the "unique id" for the PendingIntent. Any ideas please? The 70% of the functionality of my app is the widgets, and it isn't working for some users :( Thanks in advance and sorry for my English.

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• crash in calloc

  - by mmd

  I'm trying to debug a program I wrote. I ran it inside gdb and I managed to catch a SIGABRT from inside calloc(). I'm completely confused about how this can arise. Can it be a bug in gcc or even libc?? More details: My program uses OpenMP. I ran it through valgrind in single-threaded mode with no errors. I also use mmap() to load a 40GB file, but I doubt that is relevant. Inside gdb, I'm running with 30 threads. Several identical runs (same input&CL) finished correctly, until the problematic one that I caught. On the surface this suggests there might be a race condition of some type. However, the SIGABRT comes from calloc() which is out of my control. Here is some relevant gdb output: (gdb) info threads [...] * 11 Thread 0x7ffff0056700 (LWP 73449) 0x00007ffff6a948a5 in raise () from /lib64/libc.so.6 [...] (gdb) thread 11 [Switching to thread 11 (Thread 0x7ffff0056700 (LWP 73449))]#0 0x00007ffff6a948a5 in raise () from /lib64/libc.so.6 (gdb) bt #0 0x00007ffff6a948a5 in raise () from /lib64/libc.so.6 #1 0x00007ffff6a96085 in abort () from /lib64/libc.so.6 #2 0x00007ffff6ad1fe7 in __libc_message () from /lib64/libc.so.6 #3 0x00007ffff6ad7916 in malloc_printerr () from /lib64/libc.so.6 #4 0x00007ffff6adb79f in _int_malloc () from /lib64/libc.so.6 #5 0x00007ffff6adbdd6 in calloc () from /lib64/libc.so.6 #6 0x000000000040e87f in my_calloc (re=0x7fff2867ef10, st=0, options=0x632020) at gmapper/../gmapper/../common/my-alloc.h:286 #7 read_get_hit_list_per_strand (re=0x7fff2867ef10, st=0, options=0x632020) at gmapper/mapping.c:1046 #8 0x000000000041308a in read_get_hit_list (re=<value optimized out>, options=0x632010, n_options=1) at gmapper/mapping.c:1239 #9 handle_read (re=<value optimized out>, options=0x632010, n_options=1) at gmapper/mapping.c:1806 #10 0x0000000000404f35 in launch_scan_threads (.omp_data_i=<value optimized out>) at gmapper/gmapper.c:557 #11 0x00007ffff7230502 in ?? () from /usr/lib64/libgomp.so.1 #12 0x00007ffff6dfc851 in start_thread () from /lib64/libpthread.so.0 #13 0x00007ffff6b4a11d in clone () from /lib64/libc.so.6 (gdb) f 6 #6 0x000000000040e87f in my_calloc (re=0x7fff2867ef10, st=0, options=0x632020) at gmapper/../gmapper/../common/my-alloc.h:286 286 res = calloc(size, 1); (gdb) p size $2 = 814080 (gdb) The function my_calloc() is just a wrapper, but the problem is not in there, as the real calloc() call looks legit. These are the limits set in the shell: $ ulimit -a core file size (blocks, -c) 0 data seg size (kbytes, -d) unlimited scheduling priority (-e) 0 file size (blocks, -f) unlimited pending signals (-i) 2067285 max locked memory (kbytes, -l) 64 max memory size (kbytes, -m) unlimited open files (-n) 1024 pipe size (512 bytes, -p) 8 POSIX message queues (bytes, -q) 819200 real-time priority (-r) 0 stack size (kbytes, -s) 10240 cpu time (seconds, -t) unlimited max user processes (-u) 1024 virtual memory (kbytes, -v) unlimited file locks (-x) unlimited The program is not out of memory, it's using 41GB on a machine with 256GB available: $ top -b -n 1 | grep gmapper 73437 user 20 0 41.5g 16g 15g T 0.0 6.6 55:17.24 gmapper-ls $ free -m total used free shared buffers cached Mem: 258437 195567 62869 0 82 189677 -/+ buffers/cache: 5807 252629 Swap: 0 0 0 I compiled using gcc (GCC) 4.4.6 20120305 (Red Hat 4.4.6-4), with flags -g -O2 -DNDEBUG -mmmx -msse -msse2 -fopenmp -Wall -Wno-deprecated -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS.

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• A simple Python deployment problem - a whole world of pain

  - by Evgeny

  We have several Python 2.6 applications running on Linux. Some of them are Pylons web applications, others are simply long-running processes that we run from the command line using nohup. We're also using virtualenv, both in development and in production. What is the best way to deploy these applications to a production server? In development we simply get the source tree into any directory, set up a virtualenv and run - easy enough. We could do the same in production and perhaps that really is the most practical solution, but it just feels a bit wrong to run svn update in production. We've also tried fab, but it just never works first time. For every application something else goes wrong. It strikes me that the whole process is just too hard, given that what we're trying to achieve is fundamentally very simple. Here's what we want from a deployment process. We should be able to run one simple command to deploy an updated version of an application. (If the initial deployment involves a bit of extra complexity that's fine.) When we run this command it should copy certain files, either out of a Subversion repository or out of a local working copy, to a specified "environment" on the server, which probably means a different virtualenv. We have both staging and production version of the applications on the same server, so they need to somehow be kept separate. If it installs into site-packages, that's fine too, as long as it works. We have some configuration files on the server that should be preserved (ie. not overwritten or deleted by the deployment process). Some of these applications import modules from other applications, so they need to be able to reference each other as packages somehow. This is the part we've had the most trouble with! I don't care whether it works via relative imports, site-packages or whatever, as long as it works reliably in both development and production. Ideally the deployment process should automatically install external packages that our applications depend on (eg. psycopg2). That's really it! How hard can it be?

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• What to do when you need more verbs in REST

  - by Richard Levasseur

  There is another similar question to mine, but the discussion veered away from the problem I'm encounting. Say I have a system that deals with expense reports (ER). You can create and edit them, add attachments, and approve/reject them. An expense report might look like this: GET /er/1 => {"title": "Trip to NY", "totalcost": "400 USD", "comments": [ "john: Please add the total cost", "mike: done, can you approve it now?" ], "approvals": [ {"john": "Pending"}, {"finance-group": "Pending"}] } That looks fine, right? Thats what an expense report document looks like. If you want to update it, you can do this: POST /er/1 {"title": "Trip to NY 2010"} If you want to approve it, you can do this: POST /er/1/approval {"approved": true} But, what if you want to update the report and approve it at the same time? How do we do that? If you only wanted to approve, then doing a POST to something like /er/1/approval makes sense. We could put a flag in the URL, POST /er/1?approve=1, and send the data changes as the body, but that flag doesn't seem RESTful. We could put special field to be submitted, too, but that seems a bit hacky, too. If we did that, then why not send up data with attributes like set_title or add_to_cost? We could create a new resource for updating and approving, but (1) I can't think of how to name it without verbs, and (2) it doesn't seem right to name a resource based on what actions can be done to it (what happens if we add more actions?) We could have an X-Approve: True|False header, but headers seem like the wrong tool for the job. It'd also be difficult to get set headers without using javascript in a browser. We could use a custom media-type, application/approve+yes, but that seems no better than creating a new resource. We could create a temporary "batch operations" url, /er/1/batch/A. The client then sends multiple requests, perhaps POST /er/1/batch/A to update, then POST /er/1/batch/A/approval to approve, then POST /er/1/batch/A/status to end the batch. On the backend, the server queues up all the batch requests somewhere, then processes them in the same backend-transaction when it receives the "end batch processing" request. The downside with this is, obviously, that it introduces a lot of complexity. So, what is a good, general way to solve the problem of performing multiple actions in a single request? General because its easy to imagine additional actions that might be done in the same request: Suppress or send notifications (to email, chat, another system, whatever) Override some validation (maximum cost, names of dinner attendees) Trigger backend workflow that doesn't have a representation in the document.

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• How to design this ?

  - by Akku

  how can i make this entire process as 1 single event??? http://code.google.com/apis/visualization/documentation/dev/dsl_get_started.html and draw the chart on single click? I am new to servlets please guide me When a user clicks the "go " button with some input. The data goes to the servlet say "Test3". The servlet processes the data by the user and generates/feeds the data table dynamically Then I call the html page to draw the chart as shown in the tutorial link above. The problem is when I call the servlet it gives me a long json string in the browser as given in the tutorials "google.visualization.Query.setResponse({version:'0.6',status:'ok',sig:'1333639331',table:{cols:[{............................" Then when i manually call the html page to draw the chart i am see the chart. But when I call html page directly using the request dispatcher via the servlet I dont get the result. This is my code and o/p...... I need sugession as to how should be my approach to call the chart public class Test3 extends HttpServlet implements DataTableGenerator { protected void processRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { DataSourceHelper.executeDataSourceServletFlow(request, response, this , isRestrictedAccessMode() ); RequestDispatcher rd; rd = request.getRequestDispatcher("new.html");// it call's the html page which draws the chart as per the data added by the servlet..... rd.include(request, response);//forward(request, response); @Override public Capabilities getCapabilities() { return Capabilities.NONE; } protected boolean isRestrictedAccessMode() { return false; } @Override public DataTable generateDataTable(Query query, HttpServletRequest request) { // Create a data table. DataTable data = new DataTable(); ArrayList<ColumnDescription> cd = new ArrayList<ColumnDescription>(); cd.add(new ColumnDescription("name", ValueType.TEXT, "Animal name")); cd.add......... I get the following result along with unprocessed html page google.visualization.Query.setResponse({version:'0.6',statu..... <html> <head> <title>Getting Started Example</title> .... Entire html page as it is on the Browser. What I need is when a user clicks the go button the servlet should process the data and call the html page to draw the chart....Without the json string appearing on the browser.(all in one user click) What should be my approach or how should i design this.... there are no error in the code. since when i run the servlet i get the json string on the browser and then when i run the html page manually i get the chart drawn. So how can I do (servlet processing + html page drawing chart as final result) at one go without the long json string appearing on the browser. There is no problem with the html code....

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• Scala actors: receive vs react

  - by jqno

  Let me first say that I have quite a lot of Java experience, but have only recently become interested in functional languages. Recently I've started looking at Scala, which seems like a very nice language. However, I've been reading about Scala's Actor framework in Programming in Scala, and there's one thing I don't understand. In chapter 30.4 it says that using react instead of receive makes it possible to re-use threads, which is good for performance, since threads are expensive in the JVM. Does this mean that, as long as I remember to call react instead of receive, I can start as many Actors as I like? Before discovering Scala, I've been playing with Erlang, and the author of Programming Erlang boasts about spawning over 200,000 processes without breaking a sweat. I'd hate to do that with Java threads. What kind of limits am I looking at in Scala as compared to Erlang (and Java)? Also, how does this thread re-use work in Scala? Let's assume, for simplicity, that I have only one thread. Will all the actors that I start run sequentially in this thread, or will some sort of task-switching take place? For example, if I start two actors that ping-pong messages to each other, will I risk deadlock if they're started in the same thread? According to Programming in Scala, writing actors to use react is more difficult than with receive. This sounds plausible, since react doesn't return. However, the book goes on to show how you can put a react inside a loop using Actor.loop. As a result, you get loop { react { ... } } which, to me, seems pretty similar to while (true) { receive { ... } } which is used earlier in the book. Still, the book says that "in practice, programs will need at least a few receive's". So what am I missing here? What can receive do that react cannot, besides return? And why do I care? Finally, coming to the core of what I don't understand: the book keeps mentioning how using react makes it possible to discard the call stack to re-use the thread. How does that work? Why is it necessary to discard the call stack? And why can the call stack be discarded when a function terminates by throwing an exception (react), but not when it terminates by returning (receive)? I have the impression that Programming in Scala has been glossing over some of the key issues here, which is a shame, because otherwise it's a truly excellent book.

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• What happens when several Java servlet apps running on the same port ?

  - by Frank

  Something strange happened to my servlets and I think I've figured out why, yet I'm more confused. I used Netbean6.7 to develop a Paypal IPN (Instant Payment Notification) message servlet, it listens on port 8080 by default for Paypal IPN messages. I used some sample Java code from it's web site, but when it ran, only about 1 in 10 messages came through, and they looked correct, but why 1 in 10 ? Not 100% or none ? So I asked some questions here and got some advices, one in particular points me to Google's App Engine, so I downloaded it and ran the demo guestbook while my IPN servlet is still running on Netbeans, the strange thing happened, after I entered "appengine-java-sdk-1.3.2\bin\dev_appserver.cmd appengine-java-sdk-1.3.2\demos\guestbook\war" from the command prompt, I went to the following url on my browser "http://localhost:8080/", I thought I would see the Google demo guestbook page, NO, what I saw was another servlet I developed 2 years ago : "Web Academy", online course registration app. How can that happen ? I never started it, and I haven't touch that project for years. I guess because it's also listening on port 8080, so now I understand why the IPN messages only came through 1 in 10 times, because another servlet was also listening on that port and could have got the messages intended for IPN, or some how those two servlets' processes mixed up and therefore couldn't respond to Paypal properly, and failed. In order to verify some of my guesses, I turn off Netbeans, and ran the Google guestbook again at the prompt, this time on my browser http://localhost:8080/ points to the demo guestbook page. My Urls look like this : [A] Paypal IPN : http://localhost:8080/PayPal_App/PayPal_Servlet [B] Web Academy : http://localhost:8080/ So now, my questions are : <1> Why the "Web Academy" servlet was auto started when I ran the Paypal servlet ? <2> If I change the IPN listening port to 8083, would that mean I can run both of them on my PC at the same time without affecting each other ? <3> But I still don't understand, [A] and [B] look different, if a page for [A] is refreshed, it should show the Paypal content, and another page looking at [B] should show the Web Academy content, and that's exactly what happens when I started Netbeans to run the Paypal servlet, both pages show their respective content correctly side by side without interfering with each other, how come the IPN messages couldn't get through 100% of the time ? <4> In Netbeans how to assign 8080 to servlet [A] and assign port 8083 to servlet [B] ? <5> How to turn off auto start of Web Academy by Netbeans ?

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• Adobe Reader process fails when starting second instance

  - by Reddog

  In our C# WinForms application, we generate PDF files and launch Adobe Reader (or whatever the default system .pdf handler is) via the Process class. Since our PDF files can be large (approx 200K), we handle the Exited event to then clean up the temp file afterwards. The system works as required when a file is opened and then closed again. However, when a second file is opened (before closing Adobe Reader) the second process immediately exits (since Reader is now using it's MDI powers) and in our Exited handler our File.Delete call should fail because it's locked by the now joined Adobe process. However, in Reader we instead get: There was an error opening this document. This file cannot be found. The unusual thing is that if I put a debugger breakpoint before the file deletion and allow it to attempt (and fail) the deletion, then the system behaves as expected! I'm positive that the file exists and fairly positive that all handles/file streams to the file are closed before starting the process. We are launching with the following code: // Open the file for viewing/printing (if the default program supports it) var pdfProcess = new Process(); pdfProcess.StartInfo.FileName = tempFileName; if (pdfProcess.StartInfo.Verbs.Contains("open", StringComparer.InvariantCultureIgnoreCase)) { var verb = pdfProcess.StartInfo.Verbs.First(v => v.Equals("open", StringComparison.InvariantCultureIgnoreCase)); pdfProcess.StartInfo.Verb = verb; } pdfProcess.StartInfo.Arguments = "/N"; // Specifies a new window will be used! (But not definitely...) pdfProcess.SynchronizingObject = this; pdfProcess.EnableRaisingEvents = true; pdfProcess.Exited += new EventHandler(pdfProcess_Exited); _pdfProcessDictionary.Add(pdfProcess, tempFileName); pdfProcess.Start(); Note: We are using the _pdfProcessDictionary to store references to the Process objects so that they stay in scope so that Exited event can successfully be raised. Our cleanup/exited event is: void pdfProcess_Exited(object sender, EventArgs e) { Debug.Assert(!InvokeRequired); var p = sender as Process; try { if (_pdfProcessDictionary.ContainsKey(p)) { var tempFileName = _pdfProcessDictionary[p]; if (File.Exists(tempFileName)) // How else can I check if I can delete it!!?? { // NOTE: Will fail if the Adobe Reader application instance has been re-used! File.Delete(tempFileName); _pdfProcessDictionary.Remove(p); } CleanOtherFiles(); // This function will clean up files for any other previously exited processes in our dictionary } } catch (IOException ex) { // Just swallow it up, we will deal with trying to delete it at another point } } Possible solutions: Detect that the file is still open in another process Detect that the second process hasn't really been fully exited and that the file is opened in the first process instead

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• do I need to close an audio Clip?

  - by Michael

  have an application that processes real-time data and is supposed to beep when a certain event occurs. The triggering event can occur multiple times per second, and if the beep is already playing when another event triggers the code is just supposed to ignore it (as opposed to interrupting the current beep and starting a new one). Here is the basic code: Clip clickClip public void prepareProcess() { super.prepareProcess(); clickClip = null; try { clipFile = new File("C:/WINDOWS/Media/CHIMES.wav"); ais = AudioSystem.getAudioInputStream(clipFile); clickClip = AudioSystem.getClip(); clickClip.open(ais); fileIsLoaded = true; } catch (Exception ex) { clickClip = null; fileIsLoaded = false; } } public void playSound() { if (fileIsLoaded) { if ((clickClip==null) || (!clickClip.isRunning())) { try { clickClip.setFramePosition(0); clickClip.start(); } catch (Exception ex) { System.out.println("Cannot play click noise"); ex.printStackTrace(); } } } The prepareProcess method gets run once in the beginning, and the playSound method is called every time a triggering event occurs. My question is: do I need to close the clickClip object? I know I could add an actionListener to monitor for a Stop event, but since the event occurs so frequently I'm worried the extra processing is going to slow down the real-time data collection. The code seems to run fine, but my worry is memory leaks. The code above is based on an example I found while searching the net, but the example used an actionListener to close the Clip specifically "to eliminate memory leaks that would occur when the stop method wasn't implemented". My program is intended to run for hours so any memory leaks I have will cause problems. I'll be honest: I have no idea how to verify whether or not I've got a problem. I'm using Netbeans, and running the memory profiler just gave me a huge list of things that I don't know how to read. This is supposed to be the simple part of the program, and I'm spending hours on it. Any help would be greatly appreciated! Michael

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• Ajax to read updated values from XML

  - by punit

  I am creating file upload progress bar. I have a CGI script which copies the data, and here I increment the progress bar value by ONE after certain iterations. I am storing the incremented value in XML file (I also tried using plain text file). On the other side I have ajax reading incremented value from xml and depending on that it increments the DIV element. However, what happens here is, it seems to me that although the ajax reads all the incremented values but it processes it after the CGI has finished execution. That is progress bar starts execution once the file copying and other stuff in CGI is completed. My code is: AJAX:::: function polling_start() { //GETS CALLED WHEN USER HITS FILE UPLOAD BUTTON intervalID = window.setInterval(send_request,100); } window.onload = function (){ request = initXMLHttpClient(); request.overrideMimeType('text/xml'); progress = document.getElementById('progress'); } function initXMLHttpClient() { if (window.XMLHttpRequest){ // code for IE7+, Firefox, Chrome, Opera, Safari xmlhttp = new XMLHttpRequest(); } else{ // code for IE6, IE5 xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); } return xmlhttp } function send_request() { request.open("GET","progress_bar.xml",true); request.onreadystatechange = request_handler; request.send(); } function request_handler() { if (request.readyState == 4 && request.status == 200) { var level=request.responseXML.getElementsByTagName('PROGRESS')[0].firstChild; progress.style.width = progress.innerHTML = level.nodeValue + '%'; progress.style.backgroundColor = "green"; } } /****ON SERVER SIDE*********/ char xmlDat1[] = "<DOCUMENT><PROGRESS>"; char xmlDat2[] = "</PROGRESS></DOCUMENT>"; fptr = fopen("progress_bar.xml", "w"); .........OTHER STUFF.............................. ................................. if(i == inc && j<=100) { fprintf(fptr, "%s\n", "\n\n\n]"); //fprintf(fptr, "%s\n", ""); fprintf(fptr, "%s", xmlDat1); // fprintf(fptr, "%d" ,j); fprintf(fptr, "%s" ,xmlDat2); fseek(fptr, 0, SEEK_SET); /*fprintf(fptr, "%d" ,j); fseek(fptr, 0, SEEK_SET);*/ i = 0; //sleep(1); j++; } (I also tried to write in .text, but same response) Any quick response would be appreciable.

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• Event sourcing: Write event before or after updating the model

  - by Magnus

  I'm reasoning about event sourcing and often I arrive at a chicken and egg problem. Would be grateful for some hints on how to reason around this. If I execute all I/O-bound processing async (ie writing to the event log) then how do I handle, or sometimes even detect, failures? I'm using Akka Actors so processing is sequential for each event/message. I do not have any database at this time, instead I would persist all the events in an event log and then keep an aggregated state of all the events in a model stored in memory. Queries are all against this model, you can consider it to be a cache. Example Creating a new user: Validate that the user does not exist in model Persist event to journal Update model (in memory) If step 3 breaks I still have persisted my event so I can replay it at a later date. If step 2 breaks I can handle that as well gracefully. This is fine, but since step 2 is I/O-bound I figured that I should do I/O in a separate actor to free up the first actor for queries: Updating a user while allowing queries (A0 = Front end/GUI actor, A1 = Processor Actor, A2 = IO-actor, E = event bus). (A0-E-A1) Event is published to update user 'U1'. Validate that the user 'U1' exists in model (A1-A2) Persist event to journal (separate actor) (A0-E-A1-A0) Query for user 'U1' profile (A2-A1) Event is now persisted continue to update model (A0-E-A1-A0) Query for user 'U1' profile (now returns fresh data) This is appealing since queries can be processed while I/O-is churning along at it's own pace. But now I can cause myself all kinds of problems where I could have two incompatible commands (delete and then update) be persisted to the event log and crash on me when replayed up at a later date, since I do the validation before persisting the event and then update the model. My aim is to have a simple reasoning around my model (since Actor processes messages sequentially single threaded) but not be waiting for I/O-bound updates when Querying. I get the feeling I'm modeling a database which in itself is might be a problem. If things are unclear please write a comment.

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• help merging perl code routines together for file processing

  - by jdamae

  I need some perl help in putting these (2) processes/code to work together. I was able to get them working individually to test, but I need help bringing them together especially with using the loop constructs. I'm not sure if I should go with foreach..anyways the code is below. Also, any best practices would be great too as I'm learning this language. Thanks for your help. Here's the process flow I am looking for: -read a directory -look for a particular file -use the file name to strip out some key information to create a newly processed file -process the input file -create the newly processed file for each input file read (if i read in 10, I create 10 new files) Sample Recs: col1,col2,col3,col4,col5 [email protected],[email protected],8,2009-09-24 21:00:46,1 [email protected],[email protected],16,2007-08-18 22:53:12,33 [email protected],[email protected],16,2007-08-18 23:41:23,33 Here's my test code: Target Filetype: `/backups/test/foo101.name.aue-foo_p002.20110124.csv` Part 1: my $target_dir = "/backups/test/"; opendir my $dh, $target_dir or die "can't opendir $target_dir: $!"; while (defined(my $file = readdir($dh))) { next if ($file =~ /^\.+$/); #Get filename attributes if ($file =~ /^foo(\d{3})\.name\.(\w{3})-foo_p(\d{1,4})\.\d+.csv$/) { print "$1\n"; print "$2\n"; print "$3\n"; } print "$file\n"; } Part 2: use strict; use Digest::MD5 qw(md5_hex); #Create new file open (NEWFILE, ">/backups/processed/foo$1.name.$2-foo_p$3.out") || die "cannot create file"; my $data = ''; my $line1 = <>; chomp $line1; my @heading = split /,/, $line1; my ($sep1, $sep2, $eorec) = ( "^A", "^E", "^D"); while (<>) { my $digest = md5_hex($data); chomp; my (@values) = split /,/; my $extra = "__mykey__$sep1$digest$sep2" ; $extra .= "$heading[$_]$sep1$values[$_]$sep2" for (0..scalar(@values)); $data .= "$extra$eorec"; print NEWFILE "$data"; } #print $data; close (NEWFILE);

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• iPhone App is leaking memory; Instruments and Clang cannot find the leak

  - by Norbert

  Hi, i've developed an iPhone program which is kind of an image manipulation program: The user get an UIImagePickerController and selects an image. Then the program does some heavy calculating in a new thread (for responsiveness of the application). The thread has, of course, its own autorelease pool. When calculation is done, the seperated thread signals the main thread that the result can be presented. The app creates a new view controller, pushes it onto the navigation controller. In short: UIImagePickerController new thread (autorelease pool) does some heavy calculation with image data signal to main thread that it's done main thread creates view controller and pushes it onto navigation controller view controller presents image result My program works well, but if I dismiss the navigation controller's top view controller by tapping on the back button and repeat the whole process several times, my app crashes. But only on the device! Instruments cannot find any leaks (except for some minor ones which I don't feel responsible for: thread creation, NSCFString; overall about 10 kB). Even Clang static analyzer tells me that my could seems to be all right. I know that the UIImage class can cache images and objects returned from convenience methods get freed only whet their autorelease pool gets drained. But most of the time I work with CGImageRef and I use UIImage' alloc, init & release methods to free memory as soon as possible. Currently, I don't know how to isolate the problem. How would you approach this problem? Crash Log: Incident Identifier: F4C202C9-1338-48FC-80AD-46248E6C7154 CrashReporter Key: bb6f526d8b9bb680f25ea8e93bb071566ccf1776 OS Version: iPhone OS 3.1.1 (7C145) Date: 2009-09-26 14:18:57 +0200 Free pages: 372 Wired pages: 7754 Purgeable pages: 0 Largest process: _MY_APP_ Processes Name UUID Count resident pages _MY_APP_ <032690e5a9b396058418d183480a9ab3> 17766 (jettisoned) (active) debugserver <ec29691560aa0e2994f82f822181bffd> 107 syslog_relay <21e13fa2b777218bdb93982e23fb65d3> 62 notification_pro <8a7725017106a28b545fd13ed58bf98c> 64 notification_pro <8a7725017106a28b545fd13ed58bf98c> 64 afcd <98b45027fbb1350977bf1ca313dee527> 65 mediaserverd <eb8fe997a752407bea573cd3adf568d3> 319 ptpd <b17af9cf6c4ad16a557d6377378e8a1e> 142 syslogd <ec8a5bc4483638539fa1266363dee8b8> 68 BTServer <1bb74831f93b1d07c48fb46cc31c15da> 119 apsd <a639ba83e666cc1d539223923ce59581> 165 notifyd <2ed3a1166da84d8d8868e64d549cae9d> 101 CommCenter <f4239480a623fb1c35fa6c725f75b166> 161 SpringBoard <8919df8091fdfab94d9ae05f513c0ce5> 2681 (active) accessoryd <b66bcf6e77c3ee740c6a017f54226200> 90 configd <41e9d763e71dc0eda19b0afec1daee1d> 275 fairplayd <cdce5393153c3d69d23c05de1d492bd4> 108 mDNSResponder <f3ef7a6b24d4f203ed147f476385ec53> 103 lockdownd <6543492543ad16ff0707a46e512944ff> 297 launchd <73ce695fee09fc37dd70b1378af1c818> 71 **End**

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• How can I pass managed objects from one AppDomain to another?

  - by Dennis P

  I have two assemblies that I'm trying to link together. One is a sort of background process that's built with WinForms and will be designed to run as a Windows Service. I have a second project that will act as a UI for the background process whenever a user launches it. I've never tried attempting something like this with managed code before, so I've started trying to use windows messages to communicate between the two processes. I'm struggling when it comes to passing more than just IntPtrs back and forth, however. Here's the code from a control in my UI project that registers itself with the background process: public void Init() { IntPtr hwnd = IntPtr.Zero; Process[] ps = Process.GetProcessesByName("BGServiceApp"); Process mainProcess = null; if(ps == null || ps.GetLength(0) == 0) { mainProcess = LaunchApp(); } else { mainProcess = ps[0]; } SendMessage(mainProcess.MainWindowHandle, INIT_CONNECTION, this.Handle, IntPtr.Zero); } protected override void WndProc(ref Message m) { if(m.Msg == INIT_CONFIRMED && InitComplete != null) { string message = Marshal.PtrToStringAuto(m.WParam); Marshal.FreeHGlobal(m.WParam); InitComplete(message, EventArgs.Empty); } base.WndProc(ref m); } This is the code from the background process that's supposed to receive a request from the UI process to register for status updates and send a confirmation message. protected override void WndProc(ref Message m) { if(m.Msg == INIT_CONNECTION) { RegisterUIDispatcher(m.WParam); Respond(m.WParam); } if(m.Msg == UNINIT_CONNECTION) { UnregisterUIDispatcher(m.WParam); if(m_RegisteredDispatchers.Count == 0) { this.Close(); } } base.WndProc(ref m); } private void Respond(IntPtr caller) { string test = "Registration confirmed!"; IntPtr ptr = Marshal.StringToHGlobalAuto(test); SendMessage(caller, INIT_CONFIRMED, ptr, IntPtr.Zero); } } The UI process receives the INIT_CONFIRMED message from my background process, but when I try to marshal the IntPtr back into a string, I get an empty string. Is the area of heap I'm using out of scope to the other process or am I missing some security attribute maybe? Is there a better and cleaner way to go about something like this using an event driven model?

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• Array Sorting Question for News System

  - by lemonpole

  Hello all. I'm currently stuck trying to figure out how to sort my array files. I have a simple news posting system that stores the content in seperate .dat files and then stores them in an array. I numbered the files so that my array can sort them from lowest number to greatest; however, I have run into a small problem. To begin here is some more information on my system so that you can understand it better. The function that gathers my files is: function getNewsList() { $fileList = array(); // Open the actual directory if($handle = opendir(ABSPATH . ADMIN . "data")) { // Read all file from the actual directory while($file = readdir($handle)) { if(!is_dir($file)) { $fileList[] = $file; } } } // Return the array. return $fileList; } On a seperate file is the programming that processes the news post. I didn't post that code for simplicity's sake but I will explain how the files are named. The files are numbered and the part of the post's title is used... for the numbering I get a count of the array and add "1" as an offset. I get the title of the post, encode it to make it file-name-friendly and limit the amount of text so by the end of it all I end up with: // Make the variable that names the file that will contain // the post. $filename = "00{$newnumrows}_{$snipEncode}"; When running print_r on the above function I get: Array ( [0] => 0010_Mira_mi_Soledad.dat [1] => 0011_WOah.dat [2] => 0012_Sinep.dat [3] => 0013_Living_in_Warfa.dat [4] => 0014_Hello.dat [5] => 001_AS.dat [6] => 002_ASASA.dat [7] => 003_SSASAS.dat ... [13] => 009_ASADADASADAFDAF.dat ) And this is how my content is displayed. For some reason according to the array sorting 0010 comes before 001...? Is there a way I can get my array to sort 001 before 0010?

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