[Qt-interest] QSystemSemaphore::acquire return false with error QSystemSemaphore::OutOfResources after 32767 pair of (release/acquire)

[Dong Tiger]

Hi,

I used QSystemSemaphore to solve producer/consumer problem in my program. I
found a strange problem.
After 32767 acquire operations,  the semaphore stopped working. Acquiring
this semaphore returned false
with error QSystemSemaphore::OutOfResources.

I wrote a simple program to demonstrate the problem.You can try it by:
  $./a.out c  (start the consumer)
  $./a.out p  (start the producer)

Then you will see producer will exit after producing 32767 products with
error
QSystemSemaphore::OutOfResources. My environment is ubuntu8.04 + (Qt4.4.0 |
Qt4.5.2).

<code>
#include <stdint.h>
#include <signal.h>
#include <unistd.h>
#include <fcntl.h>
#include <iostream>
#include <QSystemSemaphore>
#include <QCoreApplication>

static const char *kSemKeyWrite = "TestSemWrite";
static const char *kSemKeyRead = "TestSemRead";
static const int kWriteNum = 1000;
static QSystemSemaphore *sem_read;
static QSystemSemaphore *sem_write;
static uint32_t count = 0;
bool pause_flag = false;

static void SignalHandler(int sig) {
  if (pause_flag) {
    std::cout << "Resume\n";
  } else {
    std::cout << "Pause:" << count << "\n";
  }
  pause_flag = !pause_flag;
}

int main(int argc, char **argv) {
  if (argc == 1) {
    std::cout << "Please specify mode(p(producer) or c(cousumer)\n";
    return 1;
  }
  signal(SIGINT, SignalHandler);
  if (argv[1][0] == 'c') {
    sem_read = new QSystemSemaphore(kSemKeyRead, 0,
QSystemSemaphore::Create);
    sem_write = new QSystemSemaphore(kSemKeyWrite,
                                     kWriteNum,
                                     QSystemSemaphore::Create);

    // for (int i = 0; i < 20000; i++) {
    while (1) {
      if (!sem_read->acquire()) {
        std::cout << sem_read->errorString().toUtf8().data() << ":" << count
<< "\n";
        if (sem_read->error()!= QSystemSemaphore::OutOfResources) continue;
        return 1;
      }
      sem_write->release();
      count++;
      if ((count % 10000) == 0) {
        std::cout << "P:" << count << "\n";
      }
      while (pause_flag) {
        usleep(100000);
      }
    }
  } else {
    sem_read = new QSystemSemaphore(kSemKeyRead);
    sem_write = new QSystemSemaphore(kSemKeyWrite);
    // for (int i = 0; i < 10000 + kWriteNum; i++) {
    while (1) {
      while(!sem_write->acquire()) {
        std::cout << sem_write->errorString().toUtf8().data() << ":" <<
count << "\n";
        if (sem_write->error()!= QSystemSemaphore::OutOfResources) continue;
        return 1;
      }
      sem_read->release();
      count++;
      if ((count % 10000) == 0) {
        std::cout << "C:" << count << "\n";
      }
      while (pause_flag) {
        usleep(100000);
      }
    }
  }
  return 0;
}

</code>
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