.\" Copyright (c) 2008 Linux Foundation, written by Michael Kerrisk .\" .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .TH PTHREAD_JOIN 3 2020-06-09 "Linux" "Linux Programmer's Manual" .SH NAME pthread_join \- join with a terminated thread .SH SYNOPSIS .nf .B #include .PP .BI "int pthread_join(pthread_t " thread ", void **" retval ); .fi .PP 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. .PP 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 the location pointed to by .IR retval . .PP 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 ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lb lb lb l l l. Interface Attribute Value T{ .BR pthread_join () T} Thread safety MT-Safe .TE .sp 1 .SH CONFORMING TO POSIX.1-2001, POSIX.1-2008. .SH NOTES After a successful call to .BR pthread_join (), the caller is guaranteed that the target thread has terminated. The caller may then choose to do any clean-up that is required after termination of the thread (e.g., freeing memory or other resources that were allocated to the target thread). .PP Joining with a thread that has previously been joined results in undefined behavior. .PP 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). .PP 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. .PP All of the threads in a process are peers: any thread can join with any other thread in the process. .SH EXAMPLES 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 5.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.