nptl/pthread_join_common.c

   1 /* Common definition for pthread_{timed,try}join{_np}.
   2    Copyright (C) 2017-2022 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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    <https://www.gnu.org/licenses/>.  */
  18
  19 #include "pthreadP.h"
  20 #include <atomic.h>
  21 #include <stap-probe.h>
  22 #include <time.h>
  23 #include <futex-internal.h>
  24
  25 static void
  26 cleanup (void *arg)
  27 {
  28   /* If we already changed the waiter ID, reset it.  The call cannot
  29      fail for any reason but the thread not having done that yet so
  30      there is no reason for a loop.  */
  31   struct pthread *self = THREAD_SELF;
  32   atomic_compare_exchange_weak_acquire (&arg, &self, NULL);
  33 }
  34
  35 int
  36 __pthread_clockjoin_ex (pthread_t threadid, void **thread_return,
  37                         clockid_t clockid,
  38                         const struct __timespec64 *abstime, bool block)
  39 {
  40   struct pthread *pd = (struct pthread *) threadid;
  41
  42   /* Make sure the descriptor is valid.  */
  43   if (INVALID_NOT_TERMINATED_TD_P (pd))
  44     /* Not a valid thread handle.  */
  45     return ESRCH;
  46
  47   /* Is the thread joinable?.  */
  48   if (IS_DETACHED (pd))
  49     /* We cannot wait for the thread.  */
  50     return EINVAL;
  51
  52   struct pthread *self = THREAD_SELF;
  53   int result = 0;
  54
  55   LIBC_PROBE (pthread_join, 1, threadid);
  56
  57   if ((pd == self
  58        || (self->joinid == pd
  59            && (pd->cancelhandling
  60                & (CANCELING_BITMASK | CANCELED_BITMASK | EXITING_BITMASK
  61                   | TERMINATED_BITMASK)) == 0))
  62       && !cancel_enabled_and_canceled (self->cancelhandling))
  63     /* This is a deadlock situation.  The threads are waiting for each
  64        other to finish.  Note that this is a "may" error.  To be 100%
  65        sure we catch this error we would have to lock the data
  66        structures but it is not necessary.  In the unlikely case that
  67        two threads are really caught in this situation they will
  68        deadlock.  It is the programmer's problem to figure this
  69        out.  */
  70     return EDEADLK;
  71
  72   /* Wait for the thread to finish.  If it is already locked something
  73      is wrong.  There can only be one waiter.  */
  74   else if (__glibc_unlikely (atomic_compare_exchange_weak_acquire (&pd->joinid,
  75                                                                    &self,
  76                                                                    NULL)))
  77     /* There is already somebody waiting for the thread.  */
  78     return EINVAL;
  79
  80   /* BLOCK waits either indefinitely or based on an absolute time.  POSIX also
  81      states a cancellation point shall occur for pthread_join, and we use the
  82      same rationale for posix_timedjoin_np.  Both clockwait_tid and the futex
  83      call use the cancellable variant.  */
  84   if (block)
  85     {
  86       /* During the wait we change to asynchronous cancellation.  If we
  87          are cancelled the thread we are waiting for must be marked as
  88          un-wait-ed for again.  */
  89       pthread_cleanup_push (cleanup, &pd->joinid);
  90
  91       /* We need acquire MO here so that we synchronize with the
  92          kernel's store to 0 when the clone terminates. (see above)  */
  93       pid_t tid;
  94       while ((tid = atomic_load_acquire (&pd->tid)) != 0)
  95         {
  96          /* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via
  97             futex wake-up when the clone terminates.  The memory location
  98             contains the thread ID while the clone is running and is reset to
  99             zero by the kernel afterwards.  The kernel up to version 3.16.3
 100             does not use the private futex operations for futex wake-up when
 101             the clone terminates.  */
 102           int ret = __futex_abstimed_wait_cancelable64 (
 103             (unsigned int *) &pd->tid, tid, clockid, abstime, LLL_SHARED);
 104           if (ret == ETIMEDOUT || ret == EOVERFLOW)
 105             {
 106               result = ret;
 107               break;
 108             }
 109         }
 110
 111       pthread_cleanup_pop (0);
 112     }
 113
 114   void *pd_result = pd->result;
 115   if (__glibc_likely (result == 0))
 116     {
 117       /* We mark the thread as terminated and as joined.  */
 118       pd->tid = -1;
 119
 120       /* Store the return value if the caller is interested.  */
 121       if (thread_return != NULL)
 122         *thread_return = pd_result;
 123
 124       /* Free the TCB.  */
 125       __nptl_free_tcb (pd);
 126     }
 127   else
 128     pd->joinid = NULL;
 129
 130   LIBC_PROBE (pthread_join_ret, 3, threadid, result, pd_result);
 131
 132   return result;
 133 }