nptl/cancellation.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 <setjmp.h>
  20 #include <stdlib.h>
  21 #include "pthreadP.h"
  22 #include <futex-internal.h>
  23
  24
  25 /* The next two functions are similar to pthread_setcanceltype() but
  26    more specialized for the use in the cancelable functions like write().
  27    They do not need to check parameters etc.  These functions must be
  28    AS-safe, with the exception of the actual cancellation, because they
  29    are called by wrappers around AS-safe functions like write().*/
  30 int
  31 attribute_hidden
  32 __pthread_enable_asynccancel (void)
  33 {
  34   struct pthread *self = THREAD_SELF;
  35   int oldval = THREAD_GETMEM (self, cancelhandling);
  36
  37   while (1)
  38     {
  39       int newval = oldval | CANCELTYPE_BITMASK;
  40
  41       if (newval == oldval)
  42         break;
  43
  44       int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
  45                                               oldval);
  46       if (__glibc_likely (curval == oldval))
  47         {
  48           if (CANCEL_ENABLED_AND_CANCELED_AND_ASYNCHRONOUS (newval))
  49             {
  50               THREAD_SETMEM (self, result, PTHREAD_CANCELED);
  51               __do_cancel ();
  52             }
  53
  54           break;
  55         }
  56
  57       /* Prepare the next round.  */
  58       oldval = curval;
  59     }
  60
  61   return oldval;
  62 }
  63
  64 /* See the comment for __pthread_enable_asynccancel regarding
  65    the AS-safety of this function.  */
  66 void
  67 attribute_hidden
  68 __pthread_disable_asynccancel (int oldtype)
  69 {
  70   /* If asynchronous cancellation was enabled before we do not have
  71      anything to do.  */
  72   if (oldtype & CANCELTYPE_BITMASK)
  73     return;
  74
  75   struct pthread *self = THREAD_SELF;
  76   int newval;
  77
  78   int oldval = THREAD_GETMEM (self, cancelhandling);
  79
  80   while (1)
  81     {
  82       newval = oldval & ~CANCELTYPE_BITMASK;
  83
  84       int curval = THREAD_ATOMIC_CMPXCHG_VAL (self, cancelhandling, newval,
  85                                               oldval);
  86       if (__glibc_likely (curval == oldval))
  87         break;
  88
  89       /* Prepare the next round.  */
  90       oldval = curval;
  91     }
  92
  93   /* We cannot return when we are being canceled.  Upon return the
  94      thread might be things which would have to be undone.  The
  95      following loop should loop until the cancellation signal is
  96      delivered.  */
  97   while (__builtin_expect ((newval & (CANCELING_BITMASK | CANCELED_BITMASK))
  98                            == CANCELING_BITMASK, 0))
  99     {
 100       futex_wait_simple ((unsigned int *) &self->cancelhandling, newval,
 101                          FUTEX_PRIVATE);
 102       newval = THREAD_GETMEM (self, cancelhandling);
 103     }
 104 }