libpthread default is M:N threading model, kernel thread entity is allocated on demand, things like sleep() only block thread in userland, no kernel thread will be allocated, so in your example, you won't see 5 kernel threads, only two threads are showed here, the extra thread is a signal thread, there is only one signal thread in process live cycle. libthr is 1:1, when you allocate a thread in userland, it creates a kernel thread too.
David Xu
Cyrille Lefevre wrote:
Hi,
I'm currently working on enhancements to ps w/ "Garance A Drosehn". I've just added some thread related stuffs and to see them, I'm using the following program :
#define _REENTRANT #include <pthread.h>
#define NUM_THREADS 5 #define SLEEP_TIME 10
void *sleeping(void *); pthread_t tid[NUM_THREADS];
int main(int argc, char *argv[]) { int i;
for (i = 0; i < NUM_THREADS; i++) pthread_create(&tid[i], NULL, sleeping, (void *)SLEEP_TIME); for (i = 0; i < NUM_THREADS; i++) pthread_join(tid[i], NULL); printf("main() reporting that all %d threads have terminated\n", i); return (0); }
void * sleeping(void *arg) { int sleep_time = (int)arg; printf("thread %d sleeping %d seconds ...\n", thr_self(), sleep_time); sleep(sleep_time); printf("\nthread %d awakening\n", thr_self()); return (NULL); }
then, I compile this one in 2 way :
# cc -o thread thread.c -lthr and # cc -pthread -o pthread thread.c
here is some of the "new ps" outputs :
"lwp" is the thread id and "nlwp" the the number of threads. -q switch in posix mode (aka SystemV) and -C select processes by name (a la pgrep).
# ./thread& sleep 1; ps -H -O lwp,nlwp -qC thread (thread, using -H) PID LWP NLWP TTY TIME COMMAND 85146 100005 6 ttyp0 00:00:00 thread 85146 100004 6 ttyp0 00:00:00 thread 85146 100003 6 ttyp0 00:00:00 thread 85146 100002 6 ttyp0 00:00:00 thread 85146 100001 6 ttyp0 00:00:00 thread 85146 85146 6 ttyp0 00:00:00 thread # ./pthread& sleep 1; ps -H -O lwp,nlwp -qC thread (pthread, using -H) PID LWP NLWP TTY TIME COMMAND 96689 100002 2 ttyp0 00:00:00 pthread 96689 96689 2 ttyp0 00:00:00 pthread
is it normal that -pthread only forks only 1 thread where -lthr forks 5 of them ?
# ./thread& sleep 1; ps -O lwp,nlwp -qC thread (thread ot pthread, not using -H) PID LWP NLWP TTY TIME COMMAND 73718 100005 6 ttyp0 00:00:00 thread
is it normal that the selected process is the last forked thread and not the thread owner (father) ?
PS : using -lc_r, there is no thread at all, but I suppose this is an expected behaviour.
CC -current and -hackers
Cyrille Lefevre.
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