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| .TH PTHREAD_JOIN 3 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| pthread_join \- join with a terminated thread |
| .SH SYNOPSIS |
| .nf |
| .B #include <pthread.h> |
| .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). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR pthread_join () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .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) |
