1  /* Common definition for pthread_{timed,try}join{_np}.
       2     Copyright (C) 2017-2023 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  }