nptl/pthread_cancel.c

   1 /* Copyright (C) 2002-2020 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    <https://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 #include <unistd.h>
  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           /* The cancellation handler will take care of marking the
  67              thread as canceled.  */
  68           pid_t pid = __getpid ();
  69
  70           int val = INTERNAL_SYSCALL_CALL (tgkill, pid, pd->tid,
  71                                            SIGCANCEL);
  72           if (INTERNAL_SYSCALL_ERROR_P (val))
  73             result = INTERNAL_SYSCALL_ERRNO (val);
  74
  75           break;
  76         }
  77
  78         /* A single-threaded process should be able to kill itself, since
  79            there is nothing in the POSIX specification that says that it
  80            cannot.  So we set multiple_threads to true so that cancellation
  81            points get executed.  */
  82         THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
  83 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
  84         __pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
  85 #endif
  86     }
  87   /* Mark the thread as canceled.  This has to be done
  88      atomically since other bits could be modified as well.  */
  89   while (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling, newval,
  90                                                oldval));
  91
  92   return result;
  93 }
  94 weak_alias (__pthread_cancel, pthread_cancel)
  95
  96 PTHREAD_STATIC_FN_REQUIRE (__pthread_create)