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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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PTHREAD_JOIN(3P) POSIX Programmer's Manual PTHREAD_JOIN(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
pthread_join — wait for thread termination
#include <pthread.h>
int pthread_join(pthread_t thread, void **value_ptr);
The pthread_join() function shall suspend execution of the
calling thread until the target thread terminates, unless the
target thread has already terminated. On return from a successful
pthread_join() call with a non-NULL value_ptr argument, the value
passed to pthread_exit() by the terminating thread shall be made
available in the location referenced by value_ptr. When a
pthread_join() returns successfully, the target thread has been
terminated. The results of multiple simultaneous calls to
pthread_join() specifying the same target thread are undefined.
If the thread calling pthread_join() is canceled, then the target
thread shall not be detached.
It is unspecified whether a thread that has exited but remains
unjoined counts against {PTHREAD_THREADS_MAX}.
The behavior is undefined if the value specified by the thread
argument to pthread_join() does not refer to a joinable thread.
The behavior is undefined if the value specified by the thread
argument to pthread_join() refers to the calling thread.
If successful, the pthread_join() function shall return zero;
otherwise, an error number shall be returned to indicate the
error.
The pthread_join() function may fail if:
EDEADLK
A deadlock was detected.
The pthread_join() function shall not return an error code of
[EINTR].
The following sections are informative.
An example of thread creation and deletion follows:
typedef struct {
int *ar;
long n;
} subarray;
void *
incer(void *arg)
{
long i;
for (i = 0; i < ((subarray *)arg)->n; i++)
((subarray *)arg)->ar[i]++;
}
int main(void)
{
int ar[1000000];
pthread_t th1, th2;
subarray sb1, sb2;
sb1.ar = &ar[0];
sb1.n = 500000;
(void) pthread_create(&th1, NULL, incer, &sb1);
sb2.ar = &ar[500000];
sb2.n = 500000;
(void) pthread_create(&th2, NULL, incer, &sb2);
(void) pthread_join(th1, NULL);
(void) pthread_join(th2, NULL);
return 0;
}
None.
The pthread_join() function is a convenience that has proven
useful in multi-threaded applications. It is true that a
programmer could simulate this function if it were not provided
by passing extra state as part of the argument to the
start_routine(). The terminating thread would set a flag to
indicate termination and broadcast a condition that is part of
that state; a joining thread would wait on that condition
variable. While such a technique would allow a thread to wait on
more complex conditions (for example, waiting for multiple
threads to terminate), waiting on individual thread termination
is considered widely useful. Also, including the pthread_join()
function in no way precludes a programmer from coding such
complex waits. Thus, while not a primitive, including
pthread_join() in this volume of POSIX.1‐2017 was considered
valuable.
The pthread_join() function provides a simple mechanism allowing
an application to wait for a thread to terminate. After the
thread terminates, the application may then choose to clean up
resources that were used by the thread. For instance, after
pthread_join() returns, any application-provided stack storage
could be reclaimed.
The pthread_join() or pthread_detach() function should eventually
be called for every thread that is created with the detachstate
attribute set to PTHREAD_CREATE_JOINABLE so that storage
associated with the thread may be reclaimed.
The interaction between pthread_join() and cancellation is well-
defined for the following reasons:
* The pthread_join() function, like all other non-async-cancel-
safe functions, can only be called with deferred
cancelability type.
* Cancellation cannot occur in the disabled cancelability
state.
Thus, only the default cancelability state need be considered. As
specified, either the pthread_join() call is canceled, or it
succeeds, but not both. The difference is obvious to the
application, since either a cancellation handler is run or
pthread_join() returns. There are no race conditions since
pthread_join() was called in the deferred cancelability state.
If an implementation detects that the value specified by the
thread argument to pthread_join() does not refer to a joinable
thread, it is recommended that the function should fail and
report an [EINVAL] error.
If an implementation detects that the value specified by the
thread argument to pthread_join() refers to the calling thread,
it is recommended that the function should fail and report an
[EDEADLK] error.
If an implementation detects use of a thread ID after the end of
its lifetime, it is recommended that the function should fail and
report an [ESRCH] error.
None.
pthread_create(3p), wait(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.12, Memory
Synchronization, pthread.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 PTHREAD_JOIN(3P)
Pages that refer to this page: pthread.h(0p), pthread_cancel(3p), pthread_create(3p), pthread_detach(3p), pthread_exit(3p)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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