nptl/cancellation.c

   1 /* Copyright (C) 2002-2022 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <setjmp.h>
  19 #include <stdlib.h>
  20 #include "pthreadP.h"
  21 #include <futex-internal.h>
  22
  23
  24 /* The next two functions are similar to pthread_setcanceltype() but
  25    more specialized for the use in the cancelable functions like write().
  26    They do not need to check parameters etc.  These functions must be
  27    AS-safe, with the exception of the actual cancellation, because they
  28    are called by wrappers around AS-safe functions like write().*/
  29 int
  30 __pthread_enable_asynccancel (void)
  31 {
  32   struct pthread *self = THREAD_SELF;
  33   int oldval = atomic_load_relaxed (&self->cancelhandling);
  34
  35   while (1)
  36     {
  37       int newval = oldval | CANCELTYPE_BITMASK;
  38
  39       if (newval == oldval)
  40         break;
  41
  42       if (atomic_compare_exchange_weak_acquire (&self->cancelhandling,
  43                                                 &oldval, newval))
  44         {
  45           if (cancel_enabled_and_canceled_and_async (newval))
  46             {
  47               self->result = PTHREAD_CANCELED;
  48               __do_cancel ();
  49             }
  50
  51           break;
  52         }
  53     }
  54
  55   return oldval;
  56 }
  57 libc_hidden_def (__pthread_enable_asynccancel)
  58
  59 /* See the comment for __pthread_enable_asynccancel regarding
  60    the AS-safety of this function.  */
  61 void
  62 __pthread_disable_asynccancel (int oldtype)
  63 {
  64   /* If asynchronous cancellation was enabled before we do not have
  65      anything to do.  */
  66   if (oldtype & CANCELTYPE_BITMASK)
  67     return;
  68
  69   struct pthread *self = THREAD_SELF;
  70   int newval;
  71   int oldval = atomic_load_relaxed (&self->cancelhandling);
  72   do
  73     {
  74       newval = oldval & ~CANCELTYPE_BITMASK;
  75     }
  76   while (!atomic_compare_exchange_weak_acquire (&self->cancelhandling,
  77                                                 &oldval, newval));
  78
  79   /* We cannot return when we are being canceled.  Upon return the
  80      thread might be things which would have to be undone.  The
  81      following loop should loop until the cancellation signal is
  82      delivered.  */
  83   while (__glibc_unlikely ((newval & (CANCELING_BITMASK | CANCELED_BITMASK))
  84                            == CANCELING_BITMASK))
  85     {
  86       futex_wait_simple ((unsigned int *) &self->cancelhandling, newval,
  87                          FUTEX_PRIVATE);
  88       newval = atomic_load_relaxed (&self->cancelhandling);
  89     }
  90 }
  91 libc_hidden_def (__pthread_disable_asynccancel)