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Re: Pthread-win32 races?

Sergey Fokin wrote:
Hi all.

I have some peculiarities with pthread-win32 and suppose there's a bug
in library.

Although I haven't tested the fix yet, it is possible in the current version for sem_destroy to incorrectly return EBUSY. The problem is in sem_destroy.c. In the sample case, sem_post releases the waiting thread which can then enter sem_destroy while sem_post still holds the mutex guarding the semaphore's state. The EBUSY error results from sem_destroy's "trylock" attempt to acquire that mutex. It should block instead.

I'm about to test a fix for this, which if successful will also remove another race that occurs around invalidating the destroyed semaphore.


Here's my example code:

#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>
#include <assert.h>

void * thr(void * arg)
 return 0;

int main()
   sem_t sem;
   int error = 0;
   error = sem_init(&sem, 0, 0); // OK

   pthread_t thread;
   error = pthread_create(&thread, 0, thr, &sem); // OK

   error = sem_destroy(&sem);
   if (error != 0)
       error = errno; // errno == 16 (EBUSY)
       printf("errno = %d\n", error);

pthread_join(thread, 0);

   return error;

So, here we have error 16 (0x10) in almost all runs, independently on compile options (at least i couldn't find working combination). Compiler is msvc 7.1 sp1.

I've read about some troubles with it in BUGS file, but first, this
one is unrelated to those, as I can see, second all tests from `tests'
directory run with no errors, but this one fails even with same
compile options.

When I've tried to debug, it turned out that when main() is executing
sem_destroy(), child thread is still in sem_post(). But I couldn't
find out what's going on there and supposed this is some kind of race,
this is why subject is about races.

Google didn't find similar issues about pthread-win32 library.

Really hope, this is my fault, but I have no idea where I'm wrong.

Thanks in advance.

PS I'll also try gcc for win32 and msvc8.0 later - I don't have them
on this computer.

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