libpthread/nptl/pthread_cancel.c

   1 /* Copyright (C) 2002, 2003, 2004, 2009 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 "pthreadP.h"
  22 #include "atomic.h"
  23 #include <sysdep.h>
  24 #include <unistd.h>
  25 #include <bits/kernel-features.h>
  26
  27
  28 int
  29 pthread_cancel (
  30      pthread_t th)
  31 {
  32   volatile struct pthread *pd = (volatile struct pthread *) th;
  33
  34   /* Make sure the descriptor is valid.  */
  35   if (INVALID_TD_P (pd))
  36     /* Not a valid thread handle.  */
  37     return ESRCH;
  38
  39 #ifdef SHARED
  40   pthread_cancel_init ();
  41 #endif
  42   int result = 0;
  43   int oldval;
  44   int newval;
  45   do
  46     {
  47     again:
  48       oldval = pd->cancelhandling;
  49       newval = oldval | CANCELING_BITMASK | CANCELED_BITMASK;
  50
  51       /* Avoid doing unnecessary work.  The atomic operation can
  52          potentially be expensive if the bug has to be locked and
  53          remote cache lines have to be invalidated.  */
  54       if (oldval == newval)
  55         break;
  56
  57       /* If the cancellation is handled asynchronously just send a
  58          signal.  We avoid this if possible since it's more
  59          expensive.  */
  60       if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval))
  61         {
  62           /* Mark the cancellation as "in progress".  */
  63           if (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling,
  64                                                     oldval | CANCELING_BITMASK,
  65                                                     oldval))
  66             goto again;
  67
  68           /* The cancellation handler will take care of marking the
  69              thread as canceled.  */
  70           INTERNAL_SYSCALL_DECL (err);
  71
  72           /* One comment: The PID field in the TCB can temporarily be
  73              changed (in fork).  But this must not affect this code
  74              here.  Since this function would have to be called while
  75              the thread is executing fork, it would have to happen in
  76              a signal handler.  But this is no allowed, pthread_cancel
  77              is not guaranteed to be async-safe.  */
  78           pid_t pid = getpid ();
  79           int val;
  80           val = INTERNAL_SYSCALL (tgkill, err, 3, pid, pd->tid, SIGCANCEL);
  81
  82           if (INTERNAL_SYSCALL_ERROR_P (val, err))
  83             result = INTERNAL_SYSCALL_ERRNO (val, err);
  84
  85           break;
  86         }
  87     }
  88   /* Mark the thread as canceled.  This has to be done
  89      atomically since other bits could be modified as well.  */
  90   while (atomic_compare_and_exchange_bool_acq (&pd->cancelhandling, newval,
  91                                                oldval));
  92
  93   return result;
  94 }
  95
  96 PTHREAD_STATIC_FN_REQUIRE (pthread_create)