glibc pthreads actual threads?

["Joel Soete" <jsoe0708@tiscali.be>]

Hi all,

Sorry in advance if it is not the right place to put this question.

But I just start to learn more details about OS (A. Tanenbaum book) and
by the way try to understand a bit more about [p]threads.

I found a paper with examples (what I need much of all) and so I try by
the first one: basic_example.c (which I just change a very little for my
understanding)

/* for pthreads */
#include <pthread.h>
#include <stdio.h>

/* for getpid() */
#include <sys/types.h>
#include <unistd.h>

char * buf = "abcdefghijklmnopqrstuvwxyz";
int num_pthreads = 4;
int count = 60;
int fd = 1;

void * new_thread(void * arg)
{
    int i;
    pid_t PID=getpid();


    for (i = 0; i < count; i++) {
        fprintf(stderr, "PID: %d\n", PID);
	write(fd, arg, 1); write(fd, "\n", 1);
	sleep(1);
    }
    return(NULL);
}

main()
{
   pthread_t thread;
   int i;

   for (i = 0; i < num_pthreads; i++) {
	if (pthread_create(&thread, NULL, new_thread, (void *)(buf + i))) {
	   fprintf(stderr, "error creating a new thread \n");
	   exit(1);
	}
	pthread_detach(thread);
   }
   pthread_exit(NULL);
}

Which I compile as follow (gcc-3.3):
gcc -l pthread -o basic_example basic_example.c

That runs well (on my b2k running a 2.4.20-pa35 and libc6 2.3.1-17):
[...]
PID: 31360
a
PID: 31361
b
PID: 31362
c
PID: 31363
d
PID: 31360
a
PID: 31361
b
PID: 31362
c
PID: 31363
d
[...]

But notice  a very strange behaviour:
_the pid is not the same for each thread_ ??

Having just a small sunos 5.8 with gcc-3.2.2 (but with native libpthread)
the pb does not occurs?

Is it a limit of glibc (in general or in 2.3 only?) for all linux or only
hppa?

Thanks in advance for your attention,
    Joel



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