nptl/pthread_join.c

   1 /* Copyright (C) 2002-2017 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <stdlib.h>
  21
  22 #include <atomic.h>
  23 #include "pthreadP.h"
  24
  25 #include <stap-probe.h>
  26
  27
  28 static void
  29 cleanup (void *arg)
  30 {
  31   /* If we already changed the waiter ID, reset it.  The call cannot
  32      fail for any reason but the thread not having done that yet so
  33      there is no reason for a loop.  */
  34   (void) atomic_compare_and_exchange_bool_acq ((struct pthread **) arg, NULL,
  35                                                THREAD_SELF);
  36 }
  37
  38
  39 int
  40 __pthread_join (pthread_t threadid, void **thread_return)
  41 {
  42   struct pthread *pd = (struct pthread *) threadid;
  43
  44   /* Make sure the descriptor is valid.  */
  45   if (INVALID_NOT_TERMINATED_TD_P (pd))
  46     /* Not a valid thread handle.  */
  47     return ESRCH;
  48
  49   /* Is the thread joinable?.  */
  50   if (IS_DETACHED (pd))
  51     /* We cannot wait for the thread.  */
  52     return EINVAL;
  53
  54   struct pthread *self = THREAD_SELF;
  55   int result = 0;
  56
  57   LIBC_PROBE (pthread_join, 1, threadid);
  58
  59   /* During the wait we change to asynchronous cancellation.  If we
  60      are canceled the thread we are waiting for must be marked as
  61      un-wait-ed for again.  */
  62   pthread_cleanup_push (cleanup, &pd->joinid);
  63
  64   /* Switch to asynchronous cancellation.  */
  65   int oldtype = CANCEL_ASYNC ();
  66
  67   if ((pd == self
  68        || (self->joinid == pd
  69            && (pd->cancelhandling
  70                & (CANCELING_BITMASK | CANCELED_BITMASK | EXITING_BITMASK
  71                   | TERMINATED_BITMASK)) == 0))
  72       && !CANCEL_ENABLED_AND_CANCELED (self->cancelhandling))
  73     /* This is a deadlock situation.  The threads are waiting for each
  74        other to finish.  Note that this is a "may" error.  To be 100%
  75        sure we catch this error we would have to lock the data
  76        structures but it is not necessary.  In the unlikely case that
  77        two threads are really caught in this situation they will
  78        deadlock.  It is the programmer's problem to figure this
  79        out.  */
  80     result = EDEADLK;
  81   /* Wait for the thread to finish.  If it is already locked something
  82      is wrong.  There can only be one waiter.  */
  83   else if (__builtin_expect (atomic_compare_and_exchange_bool_acq (&pd->joinid,
  84                                                                    self,
  85                                                                    NULL), 0))
  86     /* There is already somebody waiting for the thread.  */
  87     result = EINVAL;
  88   else
  89     /* Wait for the child.  */
  90     lll_wait_tid (pd->tid);
  91
  92
  93   /* Restore cancellation mode.  */
  94   CANCEL_RESET (oldtype);
  95
  96   /* Remove the handler.  */
  97   pthread_cleanup_pop (0);
  98
  99
 100   if (__glibc_likely (result == 0))
 101     {
 102       /* We mark the thread as terminated and as joined.  */
 103       pd->tid = -1;
 104
 105       /* Store the return value if the caller is interested.  */
 106       if (thread_return != NULL)
 107         *thread_return = pd->result;
 108
 109
 110       /* Free the TCB.  */
 111       __free_tcb (pd);
 112     }
 113
 114   LIBC_PROBE (pthread_join_ret, 3, threadid, result, pd->result);
 115
 116   return result;
 117 }
 118 weak_alias (__pthread_join, pthread_join)