Pthreads limit

[duncanedinburgh]

Hi all. I am trying to spawn four hundred pthreads and I am getting an error from pthread_join() with error code 0. It seems that when the 382nd thread tries to join, there's a segmentation fault. I am using gcc v 4.1.3 on ubuntu 7.10 (32 bit) on a Pentium 4 @ 2.8GHz and 512 MB of RAM. Program runs perfectly with NTHREADS < 380 and the values of _POSIX_THREAD_THREADS_MAX, etc. are all set to high numbers. Simple example code follows :

#include <iostream>
#include <unistd.h>
#include <limits.h>
 
#define NTHREADS 400
 
using namespace std;
 
void *thread_function(void *);
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
int counter = 0;
 
main()
{
    pthread_t thread_id[NTHREADS];
    int i, j;
    int foo = 0;
 
    for(i=0; i < NTHREADS; i++)
        pthread_create(&thread_id[i], NULL, thread_function, NULL);
 
    for(j=0; j < NTHREADS; j++)
        foo = pthread_join(thread_id[j], NULL); 
 
        printf("Final counter value: %d\n", counter);
}
 
void *thread_function(void *dummyPtr)
{
   printf("Thread number %ld and counter number %d\n", pthread_self(), counter);
   pthread_mutex_lock( &mutex1 );
   counter++;
   pthread_mutex_unlock( &mutex1 );
}

[duncanedinburgh]

Hi all. I am trying to spawn four hundred pthreads and I am getting an error from pthread_join() with error code 0. It seems that when the 382nd thread tries to join, there's a segmentation fault. I am using gcc v 4.1.3 on ubuntu 7.10 (32 bit) on a Pentium 4 @ 2.8GHz and 512 MB of RAM. Program runs perfectly with NTHREADS < 380 and the values of _POSIX_THREAD_THREADS_MAX, etc. are all set to high numbers. Simple example code follows :

#include <iostream>
#include <unistd.h>
#include <limits.h>
 
#define NTHREADS 400
 
using namespace std;
 
void *thread_function(void *);
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
int counter = 0;
 
main()
{
    pthread_t thread_id[NTHREADS];
    int i, j;
    int foo = 0;
 
    for(i=0; i < NTHREADS; i++)
        pthread_create(&thread_id[i], NULL, thread_function, NULL);
 
    for(j=0; j < NTHREADS; j++)
        foo = pthread_join(thread_id[j], NULL); 
 
        printf("Final counter value: %d\n", counter);
}
 
void *thread_function(void *dummyPtr)
{
   printf("Thread number %ld and counter number %d\n", pthread_self(), counter);
   pthread_mutex_lock( &mutex1 );
   counter++;
   pthread_mutex_unlock( &mutex1 );
}

[JosAH]

Hi, 400 threads are quite a few threads; can't you use a threadpool where threads
are reused?

kind regards,

Jos

p.s I'll move your question where it belongs: in the C/C++ Forum section.

[sicarie]

Please do not double post, confine your questions on the same topic (especially if they are the same question) to a single thread.

Thanks

[weaknessforcats]

Try creating your thread array on the heap. You may be running out of stack memory.

[JosAH]

Try creating your thread array on the heap. You may be running out of stack memory.

That's most likely not it, i.e. a pthread_t structure isn't that large. More likely is
that the process runs out of memory because every new thread gets its own stack
which is one or a couple of MBs per thread.

kind regards,

Jos

[weaknessforcats]

More likely is
that the process runs out of memory because every new thread gets its own stack
which is one or a couple of MBs per thread.

There's no option to use the stack of the calling thread?

[JosAH]

There's no option to use the stack of the calling thread?

That'd be extremely difficult and extremely fine grained locking would be necessary
then. Better have each thread have its own thread; they won't get in each others'
way then.

kind regards,

Jos