nptl/pthread_cancel.c

   1 /* Copyright (C) 2002-2021 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 #include <unwind-link.h>
  27 #include <stdio.h>
  28 #include <gnu/lib-names.h>
  29
  30 int
  31 __pthread_cancel (pthread_t th)
  32 {
  33   volatile struct pthread *pd = (volatile struct pthread *) th;
  34
  35   /* Make sure the descriptor is valid.  */
  36   if (INVALID_TD_P (pd))
  37     /* Not a valid thread handle.  */
  38     return ESRCH;
  39
  40 #ifdef SHARED
  41   /* Trigger an error if libgcc_s cannot be loaded.  */
  42   {
  43     struct unwind_link *unwind_link = __libc_unwind_link_get ();
  44     if (unwind_link == NULL)
  45       __libc_fatal (LIBGCC_S_SO
  46                     " must be installed for pthread_cancel to work\n");
  47   }
  48 #endif
  49   int result = 0;
  50   int oldval;
  51   int newval;
  52   do
  53     {
  54     again:
  55       oldval = pd->cancelhandling;
  56       newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;
  57
  58       /* Avoid doing unnecessary work.  The atomic operation can
  59          potentially be expensive if the bug has to be locked and
  60          remote cache lines have to be invalidated.  */
  61       if (oldval == newval)
  62         break;
  63
  64       /* If the cancellation is handled asynchronously just send a
  65          signal.  We avoid this if possible since it's more
  66          expensive.  */
  67       if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval))
  68         {
  69           /* Mark the cancellation as "in progress".  */
  70           if (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling,
  71                                                     oldval | CANCELING_BITMASK,
  72                                                     oldval))
  73             goto again;
  74
  75           /* The cancellation handler will take care of marking the
  76              thread as canceled.  */
  77           pid_t pid = __getpid ();
  78
  79           int val = INTERNAL_SYSCALL_CALL (tgkill, pid, pd->tid,
  80                                            SIGCANCEL);
  81           if (INTERNAL_SYSCALL_ERROR_P (val))
  82             result = INTERNAL_SYSCALL_ERRNO (val);
  83
  84           break;
  85         }
  86
  87         /* A single-threaded process should be able to kill itself, since
  88            there is nothing in the POSIX specification that says that it
  89            cannot.  So we set multiple_threads to true so that cancellation
  90            points get executed.  */
  91         THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
  92 #ifndef TLS_MULTIPLE_THREADS_IN_TCB
  93         __libc_multiple_threads = 1;
  94 #endif
  95     }
  96   /* Mark the thread as canceled.  This has to be done
  97      atomically since other bits could be modified as well.  */
  98   while (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling, newval,
  99                                                oldval));
 100
 101   return result;
 102 }
 103 weak_alias (__pthread_cancel, pthread_cancel)
 104
 105 PTHREAD_STATIC_FN_REQUIRE (__pthread_create)