#include <stdlib.h>
#include <pthread.h>

int main (int argc, char **argv)
{
    pthread_mutex_t m=PTHREAD_MUTEX_INITIALIZER;

    if(pthread_mutex_lock(&m)==0) printf("locked mutex\n");
    else printf("failed to lock mutex\n"), exit(1);

    if(pthread_mutex_trylock(&m)==0)
        printf("locked again\n");
    else printf("failed to lock again\n");

    return 0;
}


---

[root@grieg new]# rm -f t; gcc -o t t.c -lpthread; ldd t; ./t
        libpthread.so.0 => /lib/tls/libpthread.so.0 (0x009bb000)
        libc.so.6 => /lib/tls/libc.so.6 (0x007f5000)
        /lib/ld-linux.so.2 (0x007dc000)
locked mutex
failed to lock again


---

[root@grieg new]# rm -f t; gcc -o t t.c -pthread; ldd t; ./t
        libpthread.so.0 => /lib/tls/libpthread.so.0 (0x009bb000)
        libc.so.6 => /lib/tls/libc.so.6 (0x007f5000)
        /lib/ld-linux.so.2 (0x007dc000)
locked mutex
failed to lock again