pthread_tryjoin_np (3) - Linux Manuals

pthread_tryjoin_np: try to join with a


pthread_tryjoin_np, pthread_timedjoin_np - try to join with a terminated thread


#define _GNU_SOURCE             /* See feature_test_macros(7) */
#include <pthread.h>

int pthread_tryjoin_np(pthread_t thread, void **retval);

int pthread_timedjoin_np(pthread_t thread, void **retval,
                         const struct timespec *abstime);

Compile and link with -pthread.


These functions operate in the same way as pthread_join(3), except for the differences described on this page.

The pthread_tryjoin_np() function performs a nonblocking join with the thread thread, returning the exit status of the thread in *retval. If thread has not yet terminated, then instead of blocking, as is done by pthread_join(3), the call returns an error.

The pthread_timedjoin_np() function performs a join-with-timeout. If thread has not yet terminated, then the call blocks until a maximum time, specified in abstime, measured against the CLOCK_REALTIME clock. If the timeout expires before thread terminates, the call returns an error. The abstime argument is a structure of the following form, specifying an absolute time measured since the Epoch (see time(2)):

struct timespec {
    time_t tv_sec;     /* seconds */
    long   tv_nsec;    /* nanoseconds */ };


On success, these functions return 0; on error, they return an error number.


These functions can fail with the same errors as pthread_join(3). pthread_tryjoin_np() can in addition fail with the following error:
thread had not yet terminated at the time of the call.

pthread_timedjoin_np() can in addition fail with the following errors:

The call timed out before thread terminated.
abstime value is invalid (tv_sec is less than 0 or tv_nsec is greater than 1e9).

pthread_timedjoin_np() never returns the error EINTR.


These functions first appeared in glibc in version 2.3.3.


For an explanation of the terms used in this section, see attributes(7).
pthread_tryjoin_np(), pthread_timedjoin_np() Thread safetyMT-Safe


These functions are nonstandard GNU extensions; hence the suffix "_np" (nonportable) in the names.


The following code waits to join for up to 5 seconds:

struct timespec ts; int s;


if (clock_gettime(CLOCK_REALTIME, &ts) == -1) {
    /* Handle error */ }

ts.tv_sec += 5;

s = pthread_timedjoin_np(thread, NULL, &ts); if (s != 0) {
    /* Handle error */ }


The pthread_timedjoin_np() function measures time by internally calculating a relative sleep interval that is then measured against the CLOCK_MONOTONIC clock instead of the CLOCK_REALTIME clock. Consequently, the timeout is unaffected by discontinuous changes to the CLOCK_REALTIME clock.


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