man3/pthread_join.3

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  26 .TH PTHREAD_JOIN 3 2017-09-15 "Linux" "Linux Programmer's Manual"
  27 .SH NAME
  28 pthread_join \- join with a terminated thread
  29 .SH SYNOPSIS
  30 .nf
  31 .B #include <pthread.h>
  32 .PP
  33 .BI "int pthread_join(pthread_t " thread ", void **" retval );
  34 .fi
  35 .PP
  36 Compile and link with \fI\-pthread\fP.
  37 .SH DESCRIPTION
  38 The
  39 .BR pthread_join ()
  40 function waits for the thread specified by
  41 .IR thread
  42 to terminate.
  43 If that thread has already terminated, then
  44 .BR pthread_join ()
  45 returns immediately.
  46 The thread specified by
  47 .I thread
  48 must be joinable.
  49 .PP
  50 If
  51 .I retval
  52 is not NULL, then
  53 .BR pthread_join ()
  54 copies the exit status of the target thread
  55 (i.e., the value that the target thread supplied to
  56 .BR pthread_exit (3))
  57 into the location pointed to by
  58 .IR retval .
  59 If the target thread was canceled, then
  60 .B PTHREAD_CANCELED
  61 is placed in the location pointed to by
  62 .IR retval .
  63 .PP
  64 If multiple threads simultaneously try to join with the same thread,
  65 the results are undefined.
  66 If the thread calling
  67 .BR pthread_join ()
  68 is canceled, then the target thread will remain joinable
  69 (i.e., it will not be detached).
  70 .SH RETURN VALUE
  71 On success,
  72 .BR pthread_join ()
  73 returns 0;
  74 on error, it returns an error number.
  75 .SH ERRORS
  76 .TP
  77 .B EDEADLK
  78 A deadlock was detected
  79 .\" The following verified by testing on glibc 2.8/NPTL:
  80 (e.g., two threads tried to join with each other);
  81 or
  82 .\" The following verified by testing on glibc 2.8/NPTL:
  83 .I thread
  84 specifies the calling thread.
  85 .TP
  86 .B EINVAL
  87 .I thread
  88 is not a joinable thread.
  89 .TP
  90 .B EINVAL
  91 Another thread is already waiting to join with this thread.
  92 .\" POSIX.1-2001 does not specify this error case.
  93 .TP
  94 .B ESRCH
  95 No thread with the ID
  96 .I thread
  97 could be found.
  98 .SH ATTRIBUTES
  99 For an explanation of the terms used in this section, see
 100 .BR attributes (7).
 101 .TS
 102 allbox;
 103 lb lb lb
 104 l l l.
 105 Interface       Attribute       Value
 106 T{
 107 .BR pthread_join ()
 108 T}      Thread safety   MT-Safe
 109 .TE
 110 .sp 1
 111 .SH CONFORMING TO
 112 POSIX.1-2001, POSIX.1-2008.
 113 .SH NOTES
 114 After a successful call to
 115 .BR pthread_join (),
 116 the caller is guaranteed that the target thread has terminated.
 117 The caller may then choose to do any clean-up that is required
 118 after termination of the thread (e.g., freeing memory or other
 119 resources that were allocated to the target thread).
 120 .PP
 121 Joining with a thread that has previously been joined results in
 122 undefined behavior.
 123 .PP
 124 Failure to join with a thread that is joinable
 125 (i.e., one that is not detached),
 126 produces a "zombie thread".
 127 Avoid doing this,
 128 since each zombie thread consumes some system resources,
 129 and when enough zombie threads have accumulated,
 130 it will no longer be possible to create new threads (or processes).
 131 .PP
 132 There is no pthreads analog of
 133 .IR "waitpid(-1,\ &status,\ 0)" ,
 134 that is, "join with any terminated thread".
 135 If you believe you need this functionality,
 136 you probably need to rethink your application design.
 137 .PP
 138 All of the threads in a process are peers:
 139 any thread can join with any other thread in the process.
 140 .SH EXAMPLE
 141 See
 142 .BR pthread_create (3).
 143 .SH SEE ALSO
 144 .BR pthread_cancel (3),
 145 .BR pthread_create (3),
 146 .BR pthread_detach (3),
 147 .BR pthread_exit (3),
 148 .BR pthread_tryjoin_np (3),
 149 .BR pthreads (7)