Pthread and OpenMP deadlock

[Emmanuel Hislen]

Hi,

Is there a known issue about pthreads and openMP not being compatible??
I saw someone raise the exact same issue on the OpenMP forum but he was 
sent back to the gcc forum.

I have an FC6 machine running with:

gcc version 4.1.2 20070626 (Red Hat 4.1.2-13)

I have a simple program spawning 2 threads, each of which executes a 
simple loop using openMP.

This program is very unstable, sometimes it works, sometimes it just 
enters a deadlock.
Without the openMP pragmas it works just fine.

I can also make it stable by doing :

    omp_set_num_threads(1);

instead of:

    omp_set_num_threads(2);

but that kind of defeats the purpose :-)

I've built a more recent gcc, no luck:

gcc version 4.3.1 (GCC)

Machine used has 2 CPUs:

====================
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 6
model name      : Intel(R) Pentium(R) D CPU 3.20GHz
stepping        : 2
cpu MHz         : 3192.348
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 2
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 6
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca 
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm 
constant_tsc pni monitor ds_cpl vmx cid cx16 xtpr lahf_lm
bogomips        : 6387.66
clflush size    : 64

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 15
model           : 6
model name      : Intel(R) Pentium(R) D CPU 3.20GHz
stepping        : 2
cpu MHz         : 3192.348
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 1
cpu cores       : 2
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 6
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca 
cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe nx lm 
constant_tsc pni monitor ds_cpl vmx cid cx16 xtpr lahf_lm
bogomips        : 6383.19
clflush size    : 64
====================    omp_set_num_threads(1);


Here's the very simple program I use:

====================
#include <stdio.h>
#include <stdlib.h>
#include <omp.h>
#include <pthread.h>

#define MAX_CNT        1000000

// 
***************************************************************************
// 
***************************************************************************
//
// Thread A
void *_threadA(void* arg)
{
    int i;
    int x = 0;

    #pragma omp parallel for
    for ( i = 0; i < MAX_CNT; i++ ) {
    x += i;
    }

    printf("%s: %u\n", __FUNCTION__, x);
    return NULL;
}

// 
***************************************************************************
// 
***************************************************************************
//
// Thread B
//
void *_threadB(void* arg)
{
    int i;
    int x = 0;

    #pragma omp parallel for
    for ( i = 0; i < MAX_CNT; i++ ) {
    x += i;
    }

    printf("%s: %u\n", __FUNCTION__, x);
    return NULL;
}


// 
***************************************************************************
// ***************************** MAIN 
****************************************
// 
***************************************************************************
//
//
//
int main(int argc, char *argv[])
{
    pthread_t a_thr;
    pthread_t b_thr;
    int status;

    omp_set_num_threads(2);


    // 
------------------------------------------------------------------------
    status = pthread_create(&a_thr,
                NULL,
                _threadA,
                (void*) NULL );
    if ( status != 0 ) {
    printf("Failed to create thread A\n");
    return (-1);
    }
    // 
------------------------------------------------------------------------
    status = pthread_create(&b_thr,
                NULL,
                _threadB,
                (void*) NULL );
    if ( status != 0 ) {
    printf("Failed to create thread B\n");
    return (-1);
    }
    // 
------------------------------------------------------------------------
    status = pthread_join(a_thr, NULL);
    if ( status != 0 ) {
    printf("Failed to join thread A\n");
    return (-1);
    }

    status = pthread_join(b_thr, NULL);
    if ( status != 0 ) {
    printf("Failed to join thread B\n");
    return (-1);
    }

    return 0;
}

====================

Compiled as follows:

g++ -pthread -fopenmp omp_test.c -o omp_test



Am I missing something obvious??

Thanks,

Emmanuel.