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  • Improve disk read performance (multiple files) with threading

    - by pablo
    I need to find a method to read a big number of small files (about 300k files) as fast as possible. Reading them sequentially using FileStream and reading the entire file in a single call takes between 170 and 208 seconds (you know, you re-run, disk cache plays its role and time varies). Then I tried using PInvoke with CreateFile/ReadFile and using FILE_FLAG_SEQUENTIAL_SCAN, but I didn't appreciate any changes. I tried with several threads (divide the big set in chunks and have every thread reading its part) and this way I was able to improve speed just a little bit (not even a 5% with every new thread up to 4). Any ideas on how to find the most effective way to do this?

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  • Threading and cores

    - by Matt
    If I have X cores on my machine and I start X threads. Let's assume for the sake of argument that each thread is completely separated in terms of the memory, hdd, etc it uses. Is the OS going to know to send each thread to a core or do more time slicing on one core for multiple threads. What the question boils down to, is if I have X cores and my program must do independent calculations, should I start X threads, will they each get piped to a core, or is the presumption that because I have X cores I can start X threads completely wrong? I'm thinking it is. This is with C# --

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  • Oracle error when logging into database

    - by Bryan
    When I try to log into my db with a specific user I get this message. Below is from the alert log. I can login as system just fine. Anyone know how to figure out what is causing this? Thanks in advance for the help. ----- Error Stack Dump ----- ORA-00604: error occurred at recursive SQL level 1 ORA-01438: value larger than specified precision allowed for this column ORA-06512: at line 2 Oracle 10g OEL 5.5

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  • concurrent doubly-linked list (1 writer, n-readers)

    - by Arne
    Hi guys, I am back in the field of programming for my Diploma-thesis now and stumbled over the following issue: I need to implement a thread-safe doubly-linked list for one thread writing the list at any position (delete, insert, mutate node data) and one to many threads traversing and reading the list. I am well aware that mutexes can be used to serialize access to the list, still I presume that a naive lock around any write operation will be less than optimal. I am wondering whether there are better variants. (I am well aware that 'optimal' has not much of a practical meaning as long as no exact measure/profiling are available but this is an academic thesis after all..) I am very gratefull for code-samples as well as references to academic granted these have at least a tiny bit of practical relevance. Thanks at lot

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  • A non-blocking server with java.io

    - by Jon
    Everybody knows that java IO is blocking, and java NIO is non-blocking. In IO you will have to use the thread per client pattern, in NIO you can use one thread for all clients. Now my question follows: is it possible to make a non-blocking design using only the Java IO api. (not NIO) I was thinking about a pattern like this (obviously very simplified); List<Socket> li; for (Socket s : li) { InputStream in = s.getInputStream(); byte[] data = in.available(); in.read(data); // processData(data); (decoding packets, encoding outgoing packets } Also note that the client will always be ready for reading data. What are your opinions on this? Will this be suitable for a server that should at least hold a few hundred of clients without major performance issues?

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  • VS 2008 "Choose Data Source" wizard

    - by ELM
    Good Day, I'm using Visual Studio Professional 2008 SP 1. When I create a connection via the designer, the "Choose Data Source" dialog only lists the following data sources: Microsoft SQL Server Compact 3.5 Microsoft SQL Server Database File When I create a connection on the Server explorer the list is complete with : Microsoft SQL Server Compact 3.5, Microsoft SQL Server Database File, Microsoft SQL Server Compact, ODBC etc. Please help me out. I need to use SQL Server Compact. I have posted the same problem on the following thread with some screenshots: http://social.msdn.microsoft.com/Forums/en/vssetup/thread/906845c3-69e9-431a-ad07-7da2de684d33

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  • MPI_Bsend and MPI_Isend. How do they work ?

    - by GBBL
    Hi, using buffered send and non blocking send I was wondering how and if they implement a new level of parallelism in my application eventually generating a thread. Imagine that a slave process generates a large amount of data and want to send it to the master. My idea was to start a buffered or non blocking send then immediately begin to compute the next result. Just when I would have to send the new data I wold check if I can reuse the buffer. This would introduce a new level of parallelism in my application between CPU and communication. Does anybody knows how this is done in MPI ? Does MPI generate a new thread to handle the Bsend or Isend ? Thanks.

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  • How to generate distinct random numbers per distinct threads in .NET?

    - by mark
    Dear ladies and sirs. I have to generate 19 bit random numbers. However, there is a constraint - two threads may not generate the same random number when running certain code. The simplest solution is lock the entire code. However, I would like to know if there is a non locking solution. I thought, I can incorporate ManagedThreadId within the produced random numbers, but the ManagedThreadId documentation on the Internet mentions that it may span the whole Int32 range. Unmanaged thread id seems to be limited to 11 bits, still this leaves me with just 8 truly random bits. Are there any other ways? Somehow to utilize the Thread Local Storage, may be? Thanks.

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  • networkstream always empty!

    - by ALEX
    hey I'm writing on an Server-Client program but when my client sends something, it never reaches my server! I'm sending like this: public void Send(string s) { char[] chars = s.ToCharArray(); byte[] bytes = chars.CharToByte(); nstream.Write(bytes, 0, bytes.Length); nstream.Flush(); } and Receiving in a background thread like this void CheckIncoming(object dd) { RecievedDelegate d = (RecievedDelegate)dd; try { while (true) { List<byte> bytelist = new List<byte>(); System.Threading.Thread.Sleep(1000); int ssss; ssss = nstream.ReadByte(); if (ssss > 1) { System.Diagnostics.Debugger.Break(); } if (bytelist.Count != 0) { d.Invoke(bytelist.ToArray()); } } } catch (Exception exp) { MSGBOX("ERROR:\n" + exp.Message); } } the ssss int is never 1 whats happening here???

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  • Boost Shared Pointer: Simultaneous Read Access Across Multiple Threads

    - by Nikhil
    I have a thread A which allocates memory and assigns it to a shared pointer. Then this thread spawns 3 other threads X, Y and Z and passes a copy of the shared pointer to each. When X, Y and Z go out of scope, the memory is freed. But is there a possibility that 2 threads X, Y go out of scope at the exact same point in time and there is a race condition on reference count so instead of decrementing it by 2, it only gets decremented once. So, now the reference count newer drops to 0, so there is a memory leak. Note that, X, Y and Z are only reading the memory. Not writing or resetting the shared pointer. To cut a long story short, can there be a race condition on the reference count and can that lead to memory leaks?

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  • Does a CPU assigns a value atomically to memory?

    - by Poni
    Hi! A quick question I've been wondering about for some time; Does the CPU assign values atomically, or, is it bit by bit (say for example a 32bit integer). If it's bit by bit, could another thread accessing this exact location get a "part" of the to-be-assigned value? Think of this: I have two threads and one shared "unsigned int" variable (call it "g_uiVal"). Both threads loop. On is printing "g_uiVal" with printf("%u\n", g_uiVal). The second just increase this number. Will the printing thread ever print something that is totally not or part of "g_uiVal"'s value? In code: unsigned int g_uiVal; void thread_writer() { g_uiVal++; } void thread_reader() { while(1) printf("%u\n", g_uiVal); }

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  • C++: is it safe to read an integer variable that's being concurrently modified without locking?

    - by Hongli
    Suppose that I have an integer variable in a class, and this variable may be concurrently modified by other threads. Writes are protected by a mutex. Do I need to protect reads too? I've heard that there are some hardware architectures on which, if one thread modifies a variable, and another thread reads it, then the read result will be garbage; in this case I do need to protect reads. I've never seen such architectures though. This question assumes that a single transaction only consists of updating a single integer variable so I'm not worried about the states of any other variables that might also be involved in a transaction.

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  • IntentService android download and return file to Activity

    - by Andrew G
    I have a fairly tricky situation that I'm trying to determine the best design for. The basics are this: I'm designing a messaging system with a similar interface to email. When a user clicks a message that has an attachment, an activity is spawned that shows the text of that message along with a paper clip signaling that there is an additional attachment. At this point, I begin preloading the attachment so that when the user clicks on it - it loads more quickly. currently, when the user clicks the attachment, it prompts with a loading dialog until the download is complete at which point it loads a separate attachment viewer activity, passing in the bmp byte array. I don't ever want to save attachments to persistent storage. The difficulty I have is in supporting rotation as well as home button presses etc. The download is currently done with a thread and handler setup. Instead of this, I'd like the flow to be the following: User loads message as before, preloading begins of attachment as before (invisible to user). When the user clicks on the attachment link, the attachment viewer activity is spawned right away. If the download was done, the image is displayed. If not, a dialog is shown in THIS activity until it is done and can be displayed. Note that ideally the download never restarts or else I've wasted cycles on the preload. Obviously I need some persistent background process that is able to keep downloading and is able to call back to arbitrarily bonded Activities. It seems like the IntentService almost fits my needs as it does its work in a background thread and has the Service (non UI) lifecycle. However, will it work for my other needs? I notice that common implementations for what I want to do get a Messenger from the caller Activity so that a Message object can be sent back to a Handler in the caller's thread. This is all well and good but what happens in my case when the caller Activity is Stopped or Destroyed and the currently active Activity (the attachment viewer) is showing? Is there some way to dynamically bind a new Activity to a running IntentService so that I can send a Message back to the new Activity? The other question is on the Message object. Can I send arbitrarily large data back in this package? For instance, rather than send back that "The file was downloaded", I need to send back the byte array of the downloaded file itself since I never want to write it to disk (and yes this needs to be the case). Any advice on achieving the behavior I want is greatly appreciated. I've not been working with Android for that long and I often get confused with how to best handle asynchronous processes over the course of the Activity lifecycle especially when it comes to orientation changes and home button presses...

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  • How to pass sockets created to another Java Process

    - by whoi
    Hi; We have an application which creates many sockets which belongs to its thread, By design if this application somehow fails, all threads stop which is not wanted. So to overcome this issue, each thread must be separated from the main application, if one of the threads fails, the other ones should be running. One thing in our mind is to pass created socket to another java process, so what is the correct way? An other approach also is welcome? Waiting for your suggestions...

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  • Waiting for ServerSocket accept() to put socket into "listen" mode

    - by inazaruk
    I need a simple client-server communication in order to implement unit-test. My steps: Create server thread Wait for server thread to put server socket into listen mode ( serverSocket.accept() ) Create client Make some request, verify responses Basically, I have a problem with step #2. I can't find a way to signal me when server socket is put to "listen" state. An asynchronous call to "accept" will do in this case, but java doesn't support this (it seems to support only asynchronous channels and those are incompatible with "accept()" method according to documentation). Of cause I can put a simple "sleep", but that is not really a solution for production code. So, to summarize, I need to detect when ServerSocket has been put into listen mode without using sleeps and/or polling.

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  • Numeric GUI bottleneck

    - by Physic
    Hi all, I've made a GUI to set up and start a numerical integrator using PyQT4, Wing, QT, and Python 2.6.6, on my Mac. The thing is, when I run the integrator form the GUI, it takes very many times longer than when I crudely run the integrator from the command line. As an example, a 1000 year integration took 98 seconds on the command line and ~570 seconds from the GUI. In the GUI, the integration runs from a thread and then returns. It uses a a queue to communicate back to the GUI. Does anyone have any ideas as to where the bottleneck is? I suspect that others may be experiencing something like this just on a smaller scale. t = threading.Thread( target=self.threadsafe_start_thread, args=( self.queue, self.selected ) ) t.start() Thanks!

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  • [c#] SoundPlayer.PlaySync stopping prematurely

    - by JeffE
    I want to play a wav file synchronously on the gui thread, but my call to PlaySync is returning early (and prematurely stopping playback). The wav file is 2-3 minutes. Here's what my code looks like: //in gui code (event handler) //play first audio file JE_SP.playSound("example1.wav"); //do a few other statements doSomethingUnrelated(); //play another audio file JE_SP.playSound("example2.wav"); //library method written by me, called in gui code, but located in another assembly public static int playSound(string wavFile, bool synchronous = true, bool debug = true, string logFile = "", int loadTimeout = FIVE_MINUTES_IN_MS) { SoundPlayer sp = new SoundPlayer(); sp.LoadTimeout = loadTimeout; sp.SoundLocation = wavFile; sp.Load(); switch (synchronous) { case true: sp.PlaySync(); break; case false: sp.Play(); break; } if (debug) { string writeMe = "JE_SP: \r\n\tSoundLocation = " + sp.SoundLocation + "\r\n\t" + "Synchronous = " + synchronous.ToString(); JE_Log.logMessage(writeMe); } sp.Dispose(); sp = null; return 0; } Some things I've thought of are the load timeout, and playing the audio on another thread and then manually 'freeze' the gui by forcing the gui thread to wait for the duration of the sound file. I tried lengthening the load timeout, but that did nothing. I'm not quite sure what the best way to get the duration of a wav file is without using code written by somebody who isn't me/Microsoft. I suppose this can be calculated since I know the file size, and all of the encoding properties (bitrate, sample rate, sample size, etc) are consistent across all files I intend to play. Can somebody elaborate on how to calculate the duration of a wav file using this info? That is, if nobody has an idea about why PlaySync is returning early. Of Note: I encountered a similar problem in VB 6 a while ago, but that was caused by a timeout, which I don't suspect to be a problem here. Shorter (< 1min) files seem to play fine, so I might decide to manually edit the longer files down, then play them separately with multiple calls.

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  • What happens if you break out of a Lock() statement?

    - by cyclotis04
    I'm writing a program which listens to an incoming TcpClient and handles data when it arrives. The Listen() method is run on a separate thread within the component, so it needs to be threadsafe. If I break out of a do while loop while I'm within a lock() statement, will the lock be released? If not, how do I accomplish this? Thanks! (Any other advice on the subject of Asynchronous TCP Sockets is welcome as well.) private void Listen() { do { lock (_client) { if (!_client.Connected) break; lock (_stateLock) { if (!_listening) break; if (_client.GetStream().DataAvailable) HandleData(); } } Thread.Sleep(0); } while (true); }

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  • Why use threading data race will occur, but will not use gevent

    - by onlytiancai
    My test code is as follows, using threading, count is not 5,000,000 , so there has been data race, but using gevent, count is 5,000,000, there was no data race . Is not gevent coroutine execution will atom "count + = 1", rather than split into a one CPU instruction to execute? # -*- coding: utf-8 -*- import threading use_gevent = True use_debug = False cycles_count = 100*10000 if use_gevent: from gevent import monkey monkey.patch_thread() count = 0 class Counter(threading.Thread): def __init__(self, name): self.thread_name = name super(Counter, self).__init__(name=name) def run(self): global count for i in xrange(cycles_count): if use_debug: print '%s:%s' % (self.thread_name, count) count = count + 1 counters = [Counter('thread:%s' % i) for i in range(5)] for counter in counters: counter.start() for counter in counters: counter.join() print 'count=%s' % count

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  • database structure for threads that are editable by many users?

    - by fayer
    at the moment i have a column "user_id" in the "threads" table cause one thread belongs to an user. i want to make it like Stackoverflow that one thread can be editable by many users and you can see when they edited, what they edited, roll back changes and so on. im using symfony, is there a plugin for this? if no, are there any 3rd part libraries/plugins to download for this to integrate to existing database? cause i have no idea how to implement this. it sounds like mediawiki, something that already exists? thanks

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  • Java: Can't implement runnable on a test case: void run() collides

    - by Zombies
    So I have a test case that I want to make into a thread. I cannot extend Thread nor can I implement runnable since TestCase already has a method void run(). The compilation error I am getting is Error(62,17): method run() in class com.util.SeleneseTestCase cannot override method run() in class junit.framework.TestCase with different return type, was class junit.framework.TestResult. What I am trying to do is to scale a Selenium testcase up to perform stress testing. I am not able to use selenium grid/pushtotest.com/amazon cloud at this time (installation issues/install time/resource issues). So this really is more of a Java language issue for me.

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  • Is pthread_spin_trylock safe inside of sigsegv handler of multithreaded application?

    - by TWMouton
    I am trying to implement a handler that on SIGSEGV will collect some information such as process-id, thread-id and a backtrace and write this information to a file/pipe/socket. The problem lies in that there is the (probably pretty high) possibility that if one thread experienced a SIGSEGV that the others will shortly follow. If two threads happen to make it to the bit of code where they're writing their report out at the same time then they'll interleave their writing (to the same file). I know that I should only be using async-signal-safe functions as detailed in signal(7) I also have seen at least two cases here and video linked in top answer here where others have used pthread_spin_trylock to get around this problem. Is this a safe way to prevent the above problem?

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  • Should i use lock.lock(): in this method?

    - by user962800
    I wrote this method whose purpose is to give notice of the fact that a thread is leaving a specific block of code A thread stands for a car which is leaving a bridge so other cars can traverse it . The bridge is accessible to a given number of cars (limited capacity) and it's one way only. public void getout(int diection){ // release the lock semaphore.release(); try{ lock.lock(); //access to shared data if(direction == Car.NORTH) nNordTraversing--; //decreasing traversing threads else nSudTraversing--; bridgeCond.signal(); }finally{ lock.unlock(); } } My question is: should I use lock.lock(); or it's just nonsense? thanks in advance

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  • Multithreaded SDL error in C++

    - by wyatt
    I'm building a program in C++, using SDL, and am occasionally receiving this error: * glibc detected * ./assistant: double free or corruption (!prev) It's difficult to replicate, so I can't find exactly what's causing it, but I just added a second thread to the program, and neither thread run on its own seems to cause the error. The threads don't share any variables, though they both run the functions SDL_BlitSurface and SDL_Flip. Could running these concurrently throw up such an error, or am I barking up the wrong tree? If this is the cause, should I simply throw a mutex around all SDL calls? Thanks

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