|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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.1‐2008 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.1‐2008, Section 4.11, Memory
Synchronization, pthread.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/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 2013 PTHREAD_JOIN(3P)
Pages that refer to this page: pthread.h(0p), pthread_cancel(3p), pthread_create(3p), pthread_detach(3p), pthread_exit(3p)