pthread_join(3)

1PTHREAD_JOIN(3)            Linux Programmer's Manual           PTHREAD_JOIN(3)
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NAME

6       pthread_join - join with a terminated thread
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SYNOPSIS

9       #include <pthread.h>
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11       int pthread_join(pthread_t thread, void **retval);
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13       Compile and link with -pthread.
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DESCRIPTION

16       The pthread_join() function waits for the thread specified by thread to
17       terminate.  If that thread has already terminated, then  pthread_join()
18       returns immediately.  The thread specified by thread must be joinable.
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20       If  retval  is  not NULL, then pthread_join() copies the exit status of
21       the target thread (i.e., the value that the target thread  supplied  to
22       pthread_exit(3)) into the location pointed to by retval.  If the target
23       thread was canceled, then PTHREAD_CANCELED is placed  in  the  location
24       pointed to by retval.
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26       If  multiple  threads  simultaneously try to join with the same thread,
27       the results are undefined.  If the  thread  calling  pthread_join()  is
28       canceled,  then  the  target thread will remain joinable (i.e., it will
29       not be detached).
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RETURN VALUE

32       On success, pthread_join() returns 0; on error,  it  returns  an  error
33       number.
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ERRORS

36       EDEADLK
37              A  deadlock  was  detected (e.g., two threads tried to join with
38              each other); or thread specifies the calling thread.
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40       EINVAL thread is not a joinable thread.
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42       EINVAL Another thread is already waiting to join with this thread.
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44       ESRCH  No thread with the ID thread could be found.
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ATTRIBUTES

47       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
48       tributes(7).
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50       ┌────────────────────────────────────────────┬───────────────┬─────────┐
51       │Interface                                   │ Attribute     │ Value   │
52       ├────────────────────────────────────────────┼───────────────┼─────────┤
53       │pthread_join()                              │ Thread safety │ MT-Safe │
54       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

57       POSIX.1-2001, POSIX.1-2008.
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NOTES

60       After  a  successful  call  to pthread_join(), the caller is guaranteed
61       that the target thread has terminated.  The caller may then  choose  to
62       do any clean-up that is required after termination of the thread (e.g.,
63       freeing memory or other resources that were  allocated  to  the  target
64       thread).
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66       Joining  with a thread that has previously been joined results in unde‐
67       fined behavior.
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69       Failure to join with a thread that is joinable (i.e., one that  is  not
70       detached),  produces  a  "zombie thread".  Avoid doing this, since each
71       zombie thread consumes some system resources, and  when  enough  zombie
72       threads  have  accumulated, it will no longer be possible to create new
73       threads (or processes).
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75       There is no pthreads analog of waitpid(-1, &status, 0), that is,  "join
76       with any terminated thread".  If you believe you need this functionali‐
77       ty, you probably need to rethink your application design.
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79       All of the threads in a process are peers: any thread can join with any
80       other thread in the process.
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EXAMPLES

83       See pthread_create(3).
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COLOPHON

90       This page is part of release 5.12 of the Linux  man-pages  project.   A
91       description  of  the project, information about reporting bugs, and the
92       latest    version    of    this    page,    can     be     found     at
93       https://www.kernel.org/doc/man-pages/.
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97Linux                             2021-03-22                   PTHREAD_JOIN(3)