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• Nonblocking Tcp server

  - by hoodoos

  It's not a question really, i'm just looking for some guidelines :) I'm currently writing some abstract tcp server which should use as low number of threads as it can. Currently it works this way. I have a thread doing listening and some worker threads. Listener thread is just sits and wait for clients to connect I expect to have a single listener thread per server instance. Worker threads are doing all read/write/processing job on clients socket. So my problem is in building efficient worker process. And I came to some problem I can't really solve yet. Worker code is something like that(code is really simple just to show a place where i have my problem): List<Socket> readSockets = new List<Socket>(); List<Socket> writeSockets = new List<Socket>(); List<Socket> errorSockets = new List<Socket>(); while( true ){ Socket.Select( readSockets, writeSockets, errorSockets, 10 ); foreach( readSocket in readSockets ){ // do reading here } foreach( writeSocket in writeSockets ){ // do writing here } // POINT2 and here's the problem i will describe below } it works all smothly accept for 100% CPU utilization because of while loop being cycling all over again, if I have my clients doing send-receive-disconnect routine it's not that painful, but if I try to keep alive doing send-receive-send-receive all over again it really eats up all CPU. So my first idea was to put a sleep there, I check if all sockets have their data send and then putting Thread.Sleep in POINT2 just for 10ms, but this 10ms later on produces a huge delay of that 10ms when I want to receive next command from client socket.. For example if I don't try to "keep alive" commands are being executed within 10-15ms and with keep alive it becomes worse by atleast 10ms :( Maybe it's just a poor architecture? What can be done so my processor won't get 100% utilization and my server to react on something appear in client socket as soon as possible? Maybe somebody can point a good example of nonblocking server and architecture it should maintain?

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• Python: nonblocking read from stdout of threaded subprocess

  - by sberry2A

  I have a script (worker.py) that prints unbuffered output in the form... 1 2 3 . . . n where n is some constant number of iterations a loop in this script will make. In another script (service_controller.py) I start a number of threads, each of which starts a subprocess using subprocess.Popen(stdout=subprocess.PIPE, ...); Now, in my main thread (service_controller.py) I want to read the output of each thread's worker.py subprocess and use it to calculate an estimate for the time remaining till completion. I have all of the logic working that reads the stdout from worker.py and determines the last printed number. The problem is that I can not figure out how to do this in a non-blocking way. If I read a constant bufsize then each read will end up waiting for the same data from each of the workers. I have tried numerous ways including using fcntl, select + os.read, etc. What is my best option here? I can post my source if needed, but I figured the explanation describes the problem well enough. Thanks for any help here. EDIT Adding sample code I have a worker that starts a subprocess. class WorkerThread(threading.Thread): def __init__(self): self.completed = 0 self.process = None self.lock = threading.RLock() threading.Thread.__init__(self) def run(self): cmd = ["/path/to/script", "arg1", "arg2"] self.process = subprocess.Popen(cmd, stdout=subprocess.PIPE, bufsize=1, shell=False) #flags = fcntl.fcntl(self.process.stdout, fcntl.F_GETFL) #fcntl.fcntl(self.process.stdout.fileno(), fcntl.F_SETFL, flags | os.O_NONBLOCK) def get_completed(self): self.lock.acquire(); fd = select.select([self.process.stdout.fileno()], [], [], 5)[0] if fd: self.data += os.read(fd, 1) try: self.completed = int(self.data.split("\n")[-2]) except IndexError: pass self.lock.release() return self.completed I then have a ThreadManager. class ThreadManager(): def __init__(self): self.pool = [] self.running = [] self.lock = threading.Lock() def clean_pool(self, pool): for worker in [x for x in pool is not x.isAlive()]: worker.join() pool.remove(worker) del worker return pool def run(self, concurrent=5): while len(self.running) + len(self.pool) > 0: self.clean_pool(self.running) n = min(max(concurrent - len(self.running), 0), len(self.pool)) if n > 0: for worker in self.pool[0:n]: worker.start() self.running.extend(self.pool[0:n]) del self.pool[0:n] time.sleep(.01) for worker in self.running + self.pool: worker.join() and some code to run it. threadManager = ThreadManager() for i in xrange(0, 5): threadManager.pool.append(WorkerThread()) threadManager.run() I have stripped out a log of the other code in hopes to try to pinpoint the issue.

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• python: nonblocking subprocess, check stdout

  - by Will Cavanagh

  Ok so the problem I'm trying to solve is this: I need to run a program with some flags set, check on its progress and report back to a server. So I need my script to avoid blocking while the program executes, but I also need to be able to read the output. Unfortunately, I don't think any of the methods available from Popen will read the output without blocking. I tried the following, which is a bit hack-y (are we allowed to read and write to the same file from two different objects?) import time import subprocess from subprocess import * with open("stdout.txt", "wb") as outf: with open("stderr.txt", "wb") as errf: command = ['Path\\To\\Program.exe', 'para', 'met', 'ers'] p = subprocess.Popen(command, stdout=outf, stderr=errf) isdone = False while not isdone : with open("stdout.txt", "rb") as readoutf: #this feels wrong for line in readoutf: print(line) print("waiting...\\r\\n") if(p.poll() != None) : done = True time.sleep(1) output = p.communicate()[0] print(output) Unfortunately, Popen doesn't seem to write to my file until after the command terminates. Does anyone know of a way to do this? I'm not dedicated to using python, but I do need to send POST requests to a server in the same script, so python seemed like an easier choice than, say, shell scripting. Thanks! Will

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• If a nonblocking recv with MSG_PEEK succeeds, will a subsequent recv without MSG_PEEK also succeed?

  - by Michael Wolf

  Here's a simplified version of some code I'm working on: void stuff(int fd) { int ret1, ret2; char buffer[32]; ret1 = recv(fd, buffer, 32, MSG_PEEK | MSG_DONTWAIT); /* Error handling -- and EAGAIN handling -- would go here. Bail if necessary. Otherwise, keep going. */ /* Can this call to recv fail, setting errno to EAGAIN? */ ret2 = recv(fd, buffer, ret1, 0); } If we assume that the first call to recv succeeds, returning a value between 1 and 32, is it safe to assume that the second call will also succeed? Can ret2 ever be less than ret1? In which cases? (For clarity's sake, assume that there are no other error conditions during the second call to recv: that no signal is delivered, that it won't set ENOMEM, etc. Also assume that no other threads will look at fd. I'm on Linux, but MSG_DONTWAIT is, I believe, the only Linux-specific thing here. Assume that the right fnctl was set previously on other platforms.)

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• recv with MSG_NONBLOCK and MSG_WAITALL

  - by osgx

  Hello I want to use recv syscall with nonblocking flags MSG_NONBLOCK. But with this flag syscall can return before full request is satisfied. So, can I add MSG_WAITALL flag? Will it be nonblocking? or how should I rewrite blocking recv into the loop with nonblocking recv

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• Nonblocking texture upload on iPhone and other OpenGL ES platforms

  - by spurserh

  Hello, I am doing some work which involves drawing video frames in real time in OpenGL ES. Right now I am using glTexImage2D to transfer the data, in the absence of Pixel Buffer Objects and the like. A below answer suggests that glTexImage2D is always blocking, even if texture object referenced does is not used for any drawing. Is there a way to do a nonblocking texture upload with OpenGL ES (any version)? Thank you very much, Sean

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• Nonblocking io webserver/framework for java

  - by SeekingNonblockingIo

  Does anyone know of any node.js style webserver framework for java? I realized that having nonblocking callback behavior while handling a web request will require deep support at the webserver level. I am interested in node.js, but when I have a web server that ends up persisting data, I would like to take advantage of the static type system that Java offers. However, I want the scalability of non-blocking io.

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• How to use pipes for nonblocking IPC (UART emulation)

  - by codebauer

  I would like to write some test/emulation code that emulates a serial port connection. The real code looks like this: DUT <- UART - testtool.exe My plan is to use create a test application (CodeUnderTest.out) on linux that forks to launch testool.out with two (read & write) named pipes as arguments. But I cannot figure out how to make all the pipe IO non-blocking! The setup would look like this:. CodeUnderTest.out <- named pipes - testTool.out (lauched from CodeUnderTest.out) I have tried opening the pipes as following: open(wpipe,O_WRONLY|O_NONBLOCK); open(rpipe,O_RDONLY|O_NONBLOCK); But the write blocks until the reader opens the wpipe. Next I tried the following: open(wpipe,O_RDWR|O_NONBLOCK); open(rpipe,O_RDONLY|O_NONBLOCK); But then the reader of the first message never gets any data (doesn't block though) I also tried adding open and close calls around each message, but that didn't work either... Here is some test code: #include <stdio.h> #include <sys/types.h> #include <unistd.h> #include <fcntl.h> pid_t pid; char* rpipe, *wpipe,*x; FILE *rh,*wh; int rfd,wfd; void openrpipe( void ) { rfd = open(rpipe,O_RDONLY|O_NONBLOCK); rh = fdopen(rfd,"rb"); printf("%sopeningr %x\n",x,rh); } void openwpipe( void ) { //Fails when reader not already opened //wfd = open(wpipe,O_WRONLY|O_NONBLOCK); wfd = open(wpipe,O_RDWR|O_NONBLOCK); wh = fdopen(wfd,"wb"); printf("%sopeningw %x\n",x,wh); } void closerpipe( void ) { int i; i = fclose(rh); printf("%sclosingr %d\n",x,i); } void closewpipe( void ) { int i; i = fclose(wh); printf("%sclosingw %d\n",x,i); } void readpipe( char* expect, int len) { char buf[1024]; int i=0; printf("%sreading\n",x); while(i==0) { //printf("."); i = fread(buf,1,len,rh); } printf("%sread (%d) %s\n",x,i,buf); } void writepipe( char* data, int len) { int i,j; printf("%swriting\n",x); i = fwrite(data,1,len,rh); j = fflush(rh); //No help! printf("%sflush %d\n",x,j); printf("%swrite (%d) %s\n",x,i,data); } int main(int argc, char **argv) { rpipe = "readfifo"; wpipe = "writefifo"; x = ""; pid = fork(); if( pid == 0) { wpipe = "readfifo"; rpipe = "writefifo"; x = " "; openrpipe(); openwpipe(); writepipe("paul",4); readpipe("was",3); writepipe("here",4); closerpipe(); closewpipe(); exit(0); } openrpipe(); openwpipe(); readpipe("paul",4); writepipe("was",3); readpipe("here",4); closerpipe(); closewpipe(); return( -1 ); } BTW: To use the testocd above you need to pipes in the cwd: mkfifo ./readfifo mkfifo ./writefifo

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• Django Asynchronous Processing

  - by freyrs

  Hello all, I have a bunch of Django requests which executes some mathematical computations ( written in C and executed via a Cython module ) which may take an indeterminate amount ( on the order of 1 second ) of time to execute. Also the requests don't need to access the database. Right now everything is synchronous ( using Gunicorn with sync worker types ) but I'd like to make this asynchronous and nonblocking. I am very new to asynchronous Django, and so my question is what is the best stack for doing this. Is this sort of process something a task queue is well suited for? Would anyone recommend Tornado + Celery + RabbitMQ, or perhaps something else? Thanks in advance!

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• socket timeout and remove O_NONBLOCK option

  - by juxstapose

  Hello, I implemented a socket timeout and retry but in order to do it I had to set the socket as a non-blocking socket. However, I need the socket to block. This was my attempt at a solution to these two problems. This is not working. Subsequent send calls block but never send any data. When I connect without the select and the timeout, subsequent send calls work normally. References: C: socket connection timeout How to reset a socket back to blocking mode (after I set it to nonblocking mode)? Code: fd_set fdset; struct timeval tv; fcntl(dsock, F_SETFL, O_NONBLOCK); tv.tv_sec = theDeviceTimeout; tv.tv_usec = 0; int retries=0; logi(theLogOutput, LOG_INFO, "connecting to device socket num retrys: %i", theDeviceRetry); for(retries=0;retries<theDeviceRetry;retries++) { connect(dsock, (struct sockaddr *)&daddr, sizeof daddr); FD_ZERO(&fdset); FD_SET(dsock, &fdset); if (select(dsock + 1, NULL, &fdset, NULL, &tv) == 1) { int so_error; socklen_t slen = sizeof so_error; getsockopt(dsock, SOL_SOCKET, SO_ERROR, &so_error, &slen); if (so_error == 0) { logi(theLogOutput, LOG_INFO, "connected to socket on port %i on %s", theDevicePort, theDeviceIP); break; } else { logi(theLogOutput, LOG_WARN, "connect to %i failed on ip %s because %s retries %i", theDevicePort, theDeviceIP, strerror(errno), retries); logi(theLogOutput, LOG_WARN, "failed to connect to device %s", strerror(errno)); logi(theLogOutput, LOG_WARN, "error: %i %s", so_error, strerror(so_error)); continue; } } } int opts; opts = fcntl(dsock,F_GETFL); logi(theLogOutput, LOG_DEBUG, "clearing nonblock option %i retries %i", opts, retries); opts ^= O_NONBLOCK; fcntl(dsock, F_SETFL, opts);

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• Non-blocking read on a stream in python.

  - by Mathieu Pagé

  Hi, I'm using the subprocess module to start a subprocess and connect to it's output stream (stdout). I want to be able to execute non-blocking reads on its stdout. Is there a way to make .readline non-bloking or to check if there is data on the stream before I invoke .readline? I'd like this to be portable or at least work under Windows and Linux. here is how I do it for now (It's blocking on the .readline if no data is avaible): p = subprocess.Popen('myprogram.exe', stdout = subprocess.PIPE) str = p.stdout.readline() Thanks for your help.

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• how to do asynchronous http requests with epoll and python 3.1

  - by flow

  there is an interesting page http://scotdoyle.com/python-epoll-howto.html about how to do asnchronous / non-blocking / AIO http serving in python 3. there is the tornado web server which does include a non-blocking http client. i have managed to port parts of the server to python 3.1, but the implementation of the client requires pyCurl and seems to have problems (with one participant stating how ‘Libcurl is such a pain in the neck’, and looking at the incredibly ugly pyCurl page i doubt pyCurl will arrive in py3+ any time soon). now that epoll is available in the standard library, it should be possible to do asynchronous http requests out of the box with python. i really do not want to use asyncore or whatnot; epoll has a reputation for being the ideal tool for the task, and it is part of the python distribution, so using anything but epoll for non-blocking http is highly counterintuitive (prove me wrong if you feel like it). oh, and i feel threading is horrible. no threading. i use stackless. people further interested in the topic of asynchronous http should not miss out on this talk by peter portante at PyCon2010; also of interest is the keynote, where speaker antonio rodriguez at one point emphasizes the importance of having up-to-date web technology libraries right in the standard library.

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• Java / Groovy Socket - Detecting the socket being closed in a non-blocking way

  - by John Arrowwood

  I'm trying to create a small HTTP proxy that can re-write the request/headers as needed to suit my requirements. If one already exists, please, point me to it. Otherwise... I've written something that ALMOST works. It can do the proxy function, but not the re-write (yet). Problem is, I can't detect when the remote socket has been closed down without doing a blocking read. It is CRITICAL for the functionality of this thing that it be able to detect the socket being closed without blocking. I have SCOURED the Java API documentation, and I can't find ANY indication that it is even possible. Here's what I have: while ( this.inbound.isConnected() && this.outbound.isConnected() ) { try { while ( ( available = readFromClient.available() ) != 0 ) { if ( available > 1024 ) available = 1024 bytesRead = readFromClient.read( buffer, 0, available ) writeToServer.write( buffer, 0, bytesRead ) } while ( ( available = readFromServer.available() ) != 0 ) { if ( available > 1024 ) available = 1024 bytesRead = readFromServer.read( buffer, 0, available ) writeToClient.write( buffer, 0, bytesRead ) } } catch (e) { print e } println "Connected: " + this.inbound.isConnected() println "Bound: " + this.inbound.isBound() println "InputShutdown: " + this.inbound.isInputShutdown() println "OutputShutdown: " + this.inbound.isOutputShutdown() print "\n"; Thread.sleep( 10 ) } The tests for the socket being closed never indicate that the socket was closed. And, as I mentioned, I can't find ANY examples of how to detect the 'END OF FILE' condition on the stream without doing a blocking read. There HAS to be a way. Does anyone here know what it is?

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• Simple thread-safe non-blocking file logger class in c#

  - by Jason Renlan

  I have a web application, that will log some information to a file. I am looking for a simple thread-safe non-blocking file logger class in c#. I have little experience with threading. I known there are great logging components out there like log4Net, Enterprise Library Logging Block, ELMAH, but I do not want an external dependence for my application. I was thinking about using this queue implementation http://www.codeproject.com/KB/cpp/lockfreeq.aspx

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• Problem with non blocking fifo in bash

  - by timdel

  Hi! I'm running a few Team Fortress 2 servers and I want to write a little management script. Basically the TF2 servers are a fg process which provides a server console, so I can start the server, type status and get an answer from it: ***@purple:~/tf2$ ./start_server_testing Auto detecting CPU Using AMD Optimised binary. Server will auto-restart if there is a crash. Console initialized. [bla bla bla] Connection to Steam servers successful. VAC secure mode is activated. status hostname: Team Fortress version : 1.0.6.1/15 3883 secure udp/ip : ***.***.133.31:27600 map : ctf_2fort at: 0 x, 0 y, 0 z players : 0 (2 max) # userid name uniqueid connected ping loss state adr Great, now I want to create a script which sends the command sm_reloadadmins to all my servers. The best way I found to do this is using a fifo named pipe. Now what I want to do is having this pipe readonly and non blocking to the server process, so I can write into the pipe and the server executes it, but still I want to write via console one the server, so if I switch back to the fg process of the server and I type status I want an answer printed. I tried this (assuming serverfifo is mkfifo serverfifo): ./start_server_testing < serverfifo Not working, the server won't start until something is written to the pipe. ./start_server_testing <> serverfifo Thats actually working pretty good, I can see the console output of the server and I can write to the fifo and the server executes the commands, but I can't write via console to the server anymore. Also, if I write 'exit' to the pipe (which should end the server) and I'm running it in a screen the screen window is getting killed for some reason (wtf why?). I only need the server to read the fifo without blocking AND all my keyboard input on the server itself should be send to the server AND all server ouput should be written to the console. Is that possible? If yes, how?

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• Jetty 7 NIO issue?

  - by Continuation

  I saw this test showing Jetty 7's performance drops drastically when switched from blocking IO to NIO (95% drop): http://wiki.apache.org/HttpComponents/HttpCoreBenchmark Is this a known issue? Have you experienced it first hand? Should I be avoiding NIO on Jetty?

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• Simple, non-blocking way to sleep?

  - by OverTheRainbow

  Hello I googled for this and read some threads here, but I haven't found a simple way to have a VB.Net application sleep for a little while and still keep the application responsive: Imports System.Net Imports System.IO Imports System.Text Imports System.Text.RegularExpressions Imports System.Threading.Thread [...] 'How to keep screen frop freezing? While True ListBox1.Items.Clear() ListBox1.Items.Add("blah") 'Not much difference ListBox1.Refresh() 'Wait 1mn Sleep(60000) End While Is there really no simple, non-blocking solution to have a VB.Net application wait for a few seconds? Thank you.

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• Non-blocking TCP buffer issues.

  - by Poni

  Hi! I think I'm in a problem. I have two TCP apps connected to each other which use winsock I/O completion ports to send/receive data (non-blocking sockets). Everything works just fine until there's a data transfer burst. The sender starts sending incorrect/malformed data. I allocate the buffers I'm sending on the stack, and if I understand correctly, that's a wrong to do, because these buffers should remain as I sent them until I get the "write complete" notification from IOCP. Take this for example: void some_function() { char cBuff[1024]; // filling cBuff with some data WSASend(...); // sending cBuff, non-blocking mode // filling cBuff with other data WSASend(...); // again, sending cBuff // ..... and so forth! } If I understand correctly, each of these WSASend() calls should have its own unique buffer, and that buffer can be reused only when the send completes. Correct? Now, what strategies can I implement in order to maintain a big sack of such buffers, how should I handle them, how can I avoid performance penalty, etc'? And, if I am to use buffers that means I should copy the data to be sent from the source buffer to the temporary one, thus, I'd set SO_SNDBUF on each socket to zero, so the system will not re-copy what I already copied. Are you with me? Please let me know if I wasn't clear.

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• Is O_NONBLOCK being set a property of the file descriptor or underlying file?

  - by Daniel Trebbien

  From what I have been reading on The Open Group website on fcntl, open, read, and write, I get the impression that whether O_NONBLOCK is set on a file descriptor, and hence whether non-blocking I/O is used with the descriptor, should be a property of that file descriptor rather than the underlying file. Being a property of the file descriptor means, for example, that if I duplicate a file descriptor or open another descriptor to the same file, then I can use blocking I/O with one and non-blocking I/O with the other. Experimenting with a FIFO, however, it appears that it is not possible to have a blocking I/O descriptor and non-blocking I/O descriptor to the FIFO simultaneously (so whether O_NONBLOCK is set is a property of the underlying file [the FIFO]): #include <errno.h> #include <fcntl.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> int main(int argc, char **argv) { int fds[2]; if (pipe(fds) == -1) { fprintf(stderr, "`pipe` failed.\n"); return EXIT_FAILURE; } int fd0_dup = dup(fds[0]); if (fd0_dup <= STDERR_FILENO) { fprintf(stderr, "Failed to duplicate the read end\n"); return EXIT_FAILURE; } if (fds[0] == fd0_dup) { fprintf(stderr, "`fds[0]` should not equal `fd0_dup`.\n"); return EXIT_FAILURE; } if ((fcntl(fds[0], F_GETFL) & O_NONBLOCK)) { fprintf(stderr, "`fds[0]` should not have `O_NONBLOCK` set.\n"); return EXIT_FAILURE; } if (fcntl(fd0_dup, F_SETFL, fcntl(fd0_dup, F_GETFL) | O_NONBLOCK) == -1) { fprintf(stderr, "Failed to set `O_NONBLOCK` on `fd0_dup`\n"); return EXIT_FAILURE; } if ((fcntl(fds[0], F_GETFL) & O_NONBLOCK)) { fprintf(stderr, "`fds[0]` should still have `O_NONBLOCK` unset.\n"); return EXIT_FAILURE; // RETURNS HERE } char buf[1]; if (read(fd0_dup, buf, 1) != -1) { fprintf(stderr, "Expected `read` on `fd0_dup` to fail immediately\n"); return EXIT_FAILURE; } else if (errno != EAGAIN) { fprintf(stderr, "Expected `errno` to be `EAGAIN`\n"); return EXIT_FAILURE; } return EXIT_SUCCESS; } This leaves me thinking: is it ever possible to have a non-blocking I/O descriptor and blocking I/O descriptor to the same file and if so, does it depend on the type of file (regular file, FIFO, block special file, character special file, socket, etc.)?

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• Non blocking IO call from Django controller from a Windows service

  - by Anders

  Hi all, I have a CherryPy server with a Django application running as a Windows service, inside a controller I need to make a call to wmic, the problem is, so far I have only been able to implement a blocking operation. Does anyone have any recommendation for a non blocking operation so, at least more then one person at a time can access this controller and extract information from wmic? Thanks in advance, Anders

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• Using multiple sockets, is non-blocking or blocking with select better?

  - by JPhi1618

  Lets say I have a server program that can accept connections from 10 (or more) different clients. The clients send data at random which is received by the server, but it is certain that at least one client will be sending data every update. The server cannot wait for information to arrive because it has other processing to do. Aside from using asynchronous sockets, I see two options: Make all sockets non-blocking. In a loop, call recv on each socket and allow it to fail with WSAEWOULDBLOCK if there is no data available and if I happen to get some data, then keep it. Leave the sockets as blocking. Add all sockets to a fd_set and call select(). If the return value is non-zero (which it will be most of the time), loop through all the sockets to find the appropriate number of readable sockets with FD_ISSET() and only call recv on the readable sockets. The first option will create a lot more calls to the recv function. The second method is a bigger pain from a programming perspective because of all the FD_SET and FD_ISSET looping. Which method (or another method) is preferred? Is avoiding the overhead on letting recv fail on a non-blocking socket worth the hassle of calling select()? I think I understand both methods and I have tried both with success, but I don't know if one way is considered better or optimal. Only knowledgeable replies please!

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• Streaming files from EventMachine handler?

  - by Noah

  I am creating a streaming eventmachine server. I'm concerned about avoiding blocking IO or doing anything else to muck up the event loop. From what I've read, ruby's non-blocking IO can be used to stream files in a non-blocking way, or I can call next_tick, but I'm a little unclear about which of these approaches is preferable. Part of the problem is that I have not found a good explanation of non-blocking IO library functions in ruby. Short version: Assuming a long-lived network IO operation, several wall clock minutes of streaming per file, transfer, what is the best way to do this in eventmachine without gumming up the event loop? while 1 do file.read do |bytes| @conn.send_data bytes end end I understand that the above code will block and I'm wondering what to put in its place. Also, I cannot use the FileStreamer class that is part of eventmachine as is, because I need to manipulate the data after it's read but before it's sent. Thanks, Noah

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• In Java What is the guaranteed way to get a FileLock from FileChannel while accessing a RandomAcces

  - by narasimha.bhat

  I am trying to use FileLock lock(long position, long size,boolean shared) in FileChannel object As per the javadoc it can throw OverlappingFileLockException. When I create a test program with 2 threads lock method seems to be waiting to acquire the lock (both exclusive and non exclusive) But when the number threads increases in the acutal scenario over lapping file lock exception is thrown and processing slows down due the block at File lock table. What is the best way to acquire lock avoiding the OverlappingFileLockException ?

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• Testing a Non-blocking Queue

  - by jsw

  I've ported the non-blocking queue psuedocode here to C#. The code below is meant as a near verbatim copy of the paper. What approach would you take to test the implementation? Note: I'm running in VS2010 so I don't have CHESS support yet. using System.Threading; #pragma warning disable 0420 namespace ConcurrentCollections { class QueueNodePointer<T> { internal QueueNode<T> ptr; internal QueueNodePointer() : this(null) { } internal QueueNodePointer(QueueNode<T> ptr) { this.ptr = ptr; } } class QueueNode<T> { internal T value; internal QueueNodePointer<T> next; internal QueueNode() : this(default(T)) { } internal QueueNode(T value) { this.value = value; this.next = new QueueNodePointer<T>(); } } public class ConcurrentQueue<T> { private volatile int count = 0; private QueueNodePointer<T> qhead = new QueueNodePointer<T>(); private QueueNodePointer<T> qtail = new QueueNodePointer<T>(); public ConcurrentQueue() { var node = new QueueNode<T>(); node.next.ptr = null; this.qhead.ptr = this.qtail.ptr = node; } public int Count { get { return this.count; } } public void Enqueue(T value) { var node = new QueueNode<T>(value); node.next.ptr = null; QueueNodePointer<T> tail; QueueNodePointer<T> next; while (true) { tail = this.qtail; next = tail.ptr.next; if (tail == this.qtail) { if (next.ptr == null) { var newtail = new QueueNodePointer<T>(node); if (Interlocked.CompareExchange(ref tail.ptr.next, newtail, next) == next) { Interlocked.Increment(ref this.count); break; } else { Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(next.ptr), tail); } } } } Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(node), tail); } public T Dequeue() { T value; while (true) { var head = this.qhead; var tail = this.qtail; var next = head.ptr.next; if (head == this.qhead) { if (head.ptr == tail.ptr) { if (next.ptr == null) { return default(T); } Interlocked.CompareExchange(ref this.qtail, new QueueNodePointer<T>(next.ptr), tail); } else { value = next.ptr.value; var newhead = new QueueNodePointer<T>(next.ptr); if (Interlocked.CompareExchange(ref this.qhead, newhead, head) == head) { Interlocked.Decrement(ref this.count); break; } } } } return value; } } } #pragma warning restore 0420

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• verilog / systemverilog -- What is the behavior of blocking statements across two always blocks?

  - by miles.sherman

  I am wondering about the behavior of the below code. There are two always blocks, one is combinational to calculate the next_state signal, the other is sequential which will perform some logic and determine whether or not to shutdown the system. It does this by setting the shutdown_now signal high and then calling state <= next_state. My question is if the conditions become true that the shutdown_now signal is set (during clock cycle n) in a blocking manner before the state <= next_state line, will the state during clock cycle n+1 be SHUTDOWN or RUNNING? In other words, does the shutdown_now = 1'b1 line block across both state machines since the state signal is dependent on it through the next_state determination? enum {IDLE, RUNNING, SHUTDOWN} state, next_state; logic shutdown_now; // State machine (combinational) always_comb begin case (state) IDLE: next_state <= RUNNING; RUNNING: next_state <= shutdown ? SHUTDOWN : RUNNING; SHUTDOWN: next_state <= SHUTDOWN; default: next_state <= SHUTDOWN; endcase end // Sequential Behavior always_ff @ (posedge clk) begin // Some code here if (/*some condition) begin shutdown_now = 1'b0; end else begin shutdown_now = 1'b1; end state <= next_state; end

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