nptl/pthread_cancel.c

   1 /* Copyright (C) 2002-2016 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 <signal.h>
  21 #include <stdlib.h>
  22 #include "pthreadP.h"
  23 #include <atomic.h>
  24 #include <sysdep.h>
  25
  26
  27 int
  28 pthread_cancel (pthread_t th)
  29 {
  30   volatile struct pthread *pd = (volatile struct pthread *) th;
  31
  32   /* Make sure the descriptor is valid.  */
  33   if (INVALID_TD_P (pd))
  34     /* Not a valid thread handle.  */
  35     return ESRCH;
  36
  37 #ifdef SHARED
  38   pthread_cancel_init ();
  39 #endif
  40   int result = 0;
  41   int oldval;
  42   int newval;
  43   do
  44     {
  45     again:
  46       oldval = pd->cancelhandling;
  47       newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;
  48
  49       /* Avoid doing unnecessary work.  The atomic operation can
  50          potentially be expensive if the bug has to be locked and
  51          remote cache lines have to be invalidated.  */
  52       if (oldval == newval)
  53         break;
  54
  55       /* If the cancellation is handled asynchronously just send a
  56          signal.  We avoid this if possible since it's more
  57          expensive.  */
  58       if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval))
  59         {
  60           /* Mark the cancellation as "in progress".  */
  61           if (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling,
  62                                                     oldval | CANCELING_BITMASK,
  63                                                     oldval))
  64             goto again;
  65
  66 #ifdef SIGCANCEL
  67           /* The cancellation handler will take care of marking the
  68              thread as canceled.  */
  69           INTERNAL_SYSCALL_DECL (err);
  70
  71           /* One comment: The PID field in the TCB can temporarily be
  72              changed (in fork).  But this must not affect this code
  73              here.  Since this function would have to be called while
  74              the thread is executing fork, it would have to happen in
  75              a signal handler.  But this is no allowed, pthread_cancel
  76              is not guaranteed to be async-safe.  */
  77           int val;
  78           val = INTERNAL_SYSCALL (tgkill, err, 3,
  79                                   THREAD_GETMEM (THREAD_SELF, pid), pd->tid,
  80                                   SIGCANCEL);
  81
  82           if (INTERNAL_SYSCALL_ERROR_P (val, err))
  83             result = INTERNAL_SYSCALL_ERRNO (val, err);
  84 #else
  85           /* It should be impossible to get here at all, since
  86              pthread_setcanceltype should never have allowed
  87              PTHREAD_CANCEL_ASYNCHRONOUS to be set.  */
  88           abort ();
  89 #endif
  90
  91           break;
  92         }
  93
  94         /* A single-threaded process should be able to kill itself, since
  95            there is nothing in the POSIX specification that says that it
  96            cannot.  So we set multiple_threads to true so that cancellation
  97            points get executed.  */
  98         THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
  99 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
 100         __pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
 101 #endif
 102     }
 103   /* Mark the thread as canceled.  This has to be done
 104      atomically since other bits could be modified as well.  */
 105   while (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling, newval,
 106                                                oldval));
 107
 108   return result;
 109 }
 110
 111 PTHREAD_STATIC_FN_REQUIRE (pthread_create)