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.TH PTHREAD_JOIN 3 2008-11-27 "Linux" "Linux Programmer's Manual"
.SH NAME
pthread_join \- join with a terminated thread
.SH SYNOPSIS
.nf
.B #include <pthread.h>

.BI "int pthread_join(pthread_t " thread ", void **" retval );
.fi
.sp
Compile and link with \fI\-pthread\fP.
.SH DESCRIPTION
The
.BR pthread_join ()
function waits for the thread specified by
.IR thread
to terminate.
If that thread has already terminated, then
.BR pthread_join ()
returns immediately.
The thread specified by
.I thread
must be joinable.

If
.I retval
is not NULL, then
.BR pthread_join ()
copies the exit status of the target thread
(i.e., the value that the target thread supplied to
.BR pthread_exit (3))
into the location pointed to by
.IR *retval .
If the target thread was canceled, then
.B PTHREAD_CANCELED
is placed in
.IR *retval .

If multiple threads simultaneously try to join with the same thread,
the results are undefined.
If the thread calling
.BR pthread_join ()
is canceled, then the target thread will remain joinable
(i.e., it will not be detached).
.SH RETURN VALUE
On success,
.BR pthread_join ()
returns 0;
on error, it returns an error number.
.SH ERRORS
.TP
.B EDEADLK
A deadlock was detected
.\" The following verified by testing on glibc 2.8/NPTL:
(e.g., two threads tried to join with each other);
or
.\" The following verified by testing on glibc 2.8/NPTL:
.I thread
specifies the calling thread.
.TP
.B EINVAL
.I thread
is not a joinable thread.
.TP
.B EINVAL
Another thread is already waiting to join with this thread.
.\" POSIX.1-2001 does not specify this error case.
.TP
.B ESRCH
No thread with the ID
.I thread
could be found.
.SH CONFORMING TO
POSIX.1-2001.
.SH NOTES
After a successful call to
.BR pthread_join (),
the caller is guaranteed that the target thread has terminated.

Joining with a thread that has previously been joined results in
undefined behavior.

Failure to join with a thread that is joinable
(i.e., one that is not detached),
produces a "zombie thread".
Avoid doing this,
since each zombie thread consumes some system resources,
and when enough zombie threads have accumulated,
it will no longer be possible to create new threads (or processes).

There is no pthreads analog of
.IR "waitpid(-1,\ &status,\ 0)" ,
that is, "join with any terminated thread".
If you believe you need this functionality,
you probably need to rethink your application design.

All of the threads in a process are peers:
any thread can join with any other thread in the process.
.SH EXAMPLE
See
.BR pthread_create (3).
.SH SEE ALSO
.BR pthread_cancel (3),
.BR pthread_create (3),
.BR pthread_detach (3),
.BR pthread_exit (3),
.BR pthread_tryjoin_np (3),
.BR pthreads (7)
.SH COLOPHON
This page is part of release 3.53 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
\%http://www.kernel.org/doc/man\-pages/.
