lib/asyncsafe-spin.h

   1 /* Spin locks for communication between threads and signal handlers.
   2    Copyright (C) 2020-2024 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file 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
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Bruno Haible <bruno@clisp.org>, 2020.  */
  18
  19 #ifndef _ASYNCSAFE_SPIN_H
  20 #define _ASYNCSAFE_SPIN_H
  21
  22 /* Usual spin locks are not allowed for communication between threads and signal
  23    handlers, because the pthread_spin_* functions are not async-safe; see
  24    <https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html>
  25    section 2.4.3 Signal Actions.
  26
  27    This module provides spin locks with a similar API.  It can be used like this,
  28    both in regular multithreaded code and in signal handlers:
  29
  30        sigset_t saved_mask;
  31        asyncsafe_spin_lock (&lock, &mask, &saved_mask);
  32        do_something_contentious ();
  33        asyncsafe_spin_unlock (&lock, &saved_mask);
  34
  35    The mask you specify here is the set of signals whose handlers might want to
  36    take the same lock.
  37
  38    asyncsafe_spin_lock/unlock use pthread_sigmask, to ensure that while a thread
  39    is executing such code, no signal handler will start such code for the same
  40    lock *in the same thread* (because if this happened, the signal handler would
  41    hang!).  */
  42
  43 #include <signal.h>
  44
  45 #if defined _WIN32 && ! defined __CYGWIN__
  46 # include "windows-spin.h"
  47 typedef glwthread_spinlock_t asyncsafe_spinlock_t;
  48 # define ASYNCSAFE_SPIN_INIT GLWTHREAD_SPIN_INIT
  49 #else
  50 typedef unsigned int asyncsafe_spinlock_t;
  51 # define ASYNCSAFE_SPIN_INIT 0
  52 #endif
  53
  54 #ifdef __cplusplus
  55 extern "C" {
  56 #endif
  57
  58 extern void asyncsafe_spin_init (asyncsafe_spinlock_t *lock);
  59 extern void asyncsafe_spin_lock (asyncsafe_spinlock_t *lock,
  60                                  const sigset_t *mask, sigset_t *saved_mask);
  61 extern void asyncsafe_spin_unlock (asyncsafe_spinlock_t *lock,
  62                                    const sigset_t *saved_mask);
  63 extern void asyncsafe_spin_destroy (asyncsafe_spinlock_t *lock);
  64
  65 #ifdef __cplusplus
  66 }
  67 #endif
  68
  69 #endif /* _ASYNCSAFE_SPIN_H */