File: pthread_cancel.c

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/* Copyright (C) 2002-2016 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include "pthreadP.h"
#include <atomic.h>
#include <sysdep.h>
#include <unistd.h>

int
pthread_cancel (pthread_t th)
{
  volatile struct pthread *pd = (volatile struct pthread *) th;

  /* Make sure the descriptor is valid.  */
  if (INVALID_TD_P (pd))
    /* Not a valid thread handle.  */
    return ESRCH;

#ifdef SHARED
  pthread_cancel_init ();
#endif
  int result = 0;
  int oldval;
  int newval;
  do
    {
    again:
      oldval = pd->cancelhandling;
      newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;

      /* Avoid doing unnecessary work.  The atomic operation can
	 potentially be expensive if the bug has to be locked and
	 remote cache lines have to be invalidated.  */
      if (oldval == newval)
	break;

      /* If the cancellation is handled asynchronously just send a
	 signal.  We avoid this if possible since it's more
	 expensive.  */
      if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval))
	{
	  /* Mark the cancellation as "in progress".  */
	  if (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling,
						    oldval | CANCELING_BITMASK,
						    oldval))
	    goto again;

#ifdef SIGCANCEL
	  /* The cancellation handler will take care of marking the
	     thread as canceled.  */
	  pid_t pid = getpid ();

	  INTERNAL_SYSCALL_DECL (err);
	  int val = INTERNAL_SYSCALL_CALL (tgkill, err, pid, pd->tid,
					   SIGCANCEL);
	  if (INTERNAL_SYSCALL_ERROR_P (val, err))
	    result = INTERNAL_SYSCALL_ERRNO (val, err);
#else
          /* It should be impossible to get here at all, since
             pthread_setcanceltype should never have allowed
             PTHREAD_CANCEL_ASYNCHRONOUS to be set.  */
          abort ();
#endif

	  break;
	}

	/* A single-threaded process should be able to kill itself, since
	   there is nothing in the POSIX specification that says that it
	   cannot.  So we set multiple_threads to true so that cancellation
	   points get executed.  */
	THREAD_SETMEM (THREAD_SELF, header.multiple_threads, 1);
#ifndef TLS_MULTIPLE_THREADS_IN_TCB
	__pthread_multiple_threads = *__libc_multiple_threads_ptr = 1;
#endif
    }
  /* Mark the thread as canceled.  This has to be done
     atomically since other bits could be modified as well.  */
  while (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling, newval,
					       oldval));

  return result;
}

PTHREAD_STATIC_FN_REQUIRE (pthread_create)