text: /* POSIX compatible signal blocking.
     Copyright (C) 2006-2020 Free Software Foundation, Inc.
     Written by Bruno Haible <bruno@clisp.org>, 2006.
  
     This program is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 3 of the License, or
     (at your option) any later version.
  
     This program 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 General Public License for more details.
  
     You should have received a copy of the GNU General Public License
     along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  
  #include <config.h>
  
  /* Specification.  */
  #include <signal.h>
  
  #include <errno.h>
  #include <stdint.h>
  #include <stdlib.h>
  
  #if HAVE_MSVC_INVALID_PARAMETER_HANDLER
  # include "msvc-inval.h"
  #endif
  
  /* We assume that a platform without POSIX signal blocking functions
     also does not have the POSIX sigaction() function, only the
     signal() function.  We also assume signal() has SysV semantics,
     where any handler is uninstalled prior to being invoked.  This is
     true for native Windows platforms.  */
  
  /* We use raw signal(), but also provide a wrapper rpl_signal() so
     that applications can query or change a blocked signal.  */
  #undef signal
  
  /* Provide invalid signal numbers as fallbacks if the uncatchable
     signals are not defined.  */
  #ifndef SIGKILL
  # define SIGKILL (-1)
  #endif
  #ifndef SIGSTOP
  # define SIGSTOP (-1)
  #endif
  
  /* On native Windows, as of 2008, the signal SIGABRT_COMPAT is an alias
     for the signal SIGABRT.  Only one signal handler is stored for both
     SIGABRT and SIGABRT_COMPAT.  SIGABRT_COMPAT is not a signal of its own.  */
  #if defined _WIN32 && ! defined __CYGWIN__
  # undef SIGABRT_COMPAT
  # define SIGABRT_COMPAT 6
  #endif
  #ifdef SIGABRT_COMPAT
  # define SIGABRT_COMPAT_MASK (1U << SIGABRT_COMPAT)
  #else
  # define SIGABRT_COMPAT_MASK 0
  #endif
  
  typedef void (*handler_t) (int);
  
  #if HAVE_MSVC_INVALID_PARAMETER_HANDLER
  static handler_t
  signal_nothrow (int sig, handler_t handler)
  {
    handler_t result;
  
    TRY_MSVC_INVAL
      {
        result = signal (sig, handler);
      }
    CATCH_MSVC_INVAL
      {
        result = SIG_ERR;
        errno = EINVAL;
      }
    DONE_MSVC_INVAL;
  
    return result;
  }
  # define signal signal_nothrow
  #endif
  
  /* Handling of gnulib defined signals.  */
  
  #if GNULIB_defined_SIGPIPE
  static handler_t SIGPIPE_handler = SIG_DFL;
  #endif
  
  #if GNULIB_defined_SIGPIPE
  static handler_t
  ext_signal (int sig, handler_t handler)
  {
    switch (sig)
      {
      case SIGPIPE:
        {
          handler_t old_handler = SIGPIPE_handler;
          SIGPIPE_handler = handler;
          return old_handler;
        }
      default: /* System defined signal */
        return signal (sig, handler);
      }
  }
  # undef signal
  # define signal ext_signal
  #endif
  
  int
  sigismember (const sigset_t *set, int sig)
  {
    if (sig >= 0 && sig < NSIG)
      {
        #ifdef SIGABRT_COMPAT
        if (sig == SIGABRT_COMPAT)
          sig = SIGABRT;
        #endif
  
        return (*set >> sig) & 1;
      }
    else
      return 0;
  }
  
  int
  sigemptyset (sigset_t *set)
  {
    *set = 0;
    return 0;
  }
  
  int
  sigaddset (sigset_t *set, int sig)
  {
    if (sig >= 0 && sig < NSIG)
      {
        #ifdef SIGABRT_COMPAT
        if (sig == SIGABRT_COMPAT)
          sig = SIGABRT;
        #endif
  
        *set |= 1U << sig;
        return 0;
      }
    else
      {
        errno = EINVAL;
        return -1;
      }
  }
  
  int
  sigdelset (sigset_t *set, int sig)
  {
    if (sig >= 0 && sig < NSIG)
      {
        #ifdef SIGABRT_COMPAT
        if (sig == SIGABRT_COMPAT)
          sig = SIGABRT;
        #endif
  
        *set &= ~(1U << sig);
        return 0;
      }
    else
      {
        errno = EINVAL;
        return -1;
      }
  }
  
  
  int
  sigfillset (sigset_t *set)
  {
    *set = ((2U << (NSIG - 1)) - 1) & ~ SIGABRT_COMPAT_MASK;
    return 0;
  }
  
  /* Set of currently blocked signals.  */
  static volatile sigset_t blocked_set /* = 0 */;
  
  /* Set of currently blocked and pending signals.  */
  static volatile sig_atomic_t pending_array[NSIG] /* = { 0 } */;
  
  /* Signal handler that is installed for blocked signals.  */
  static void
  blocked_handler (int sig)
  {
    /* Reinstall the handler, in case the signal occurs multiple times
       while blocked.  There is an inherent race where an asynchronous
       signal in between when the kernel uninstalled the handler and
       when we reinstall it will trigger the default handler; oh
       well.  */
    signal (sig, blocked_handler);
    if (sig >= 0 && sig < NSIG)
      pending_array[sig] = 1;
  }
  
  int
  sigpending (sigset_t *set)
  {
    sigset_t pending = 0;
    int sig;
  
    for (sig = 0; sig < NSIG; sig++)
      if (pending_array[sig])
        pending |= 1U << sig;
    *set = pending;
    return 0;
  }
  
  /* The previous signal handlers.
     Only the array elements corresponding to blocked signals are relevant.  */
  static volatile handler_t old_handlers[NSIG];
  
  int
  sigprocmask (int operation, const sigset_t *set, sigset_t *old_set)
  {
    if (old_set != NULL)
      *old_set = blocked_set;
  
    if (set != NULL)
      {
        sigset_t new_blocked_set;
        sigset_t to_unblock;
        sigset_t to_block;
  
        switch (operation)
          {
          case SIG_BLOCK:
            new_blocked_set = blocked_set | *set;
            break;
          case SIG_SETMASK:
            new_blocked_set = *set;
            break;
          case SIG_UNBLOCK:
            new_blocked_set = blocked_set & ~*set;
            break;
          default:
            errno = EINVAL;
            return -1;
          }
        to_unblock = blocked_set & ~new_blocked_set;
        to_block = new_blocked_set & ~blocked_set;
  
        if (to_block != 0)
          {
            int sig;
  
            for (sig = 0; sig < NSIG; sig++)
              if ((to_block >> sig) & 1)
                {
                  pending_array[sig] = 0;
                  if ((old_handlers[sig] = signal (sig, blocked_handler)) != SIG_ERR)
                    blocked_set |= 1U << sig;
                }
          }
  
        if (to_unblock != 0)
          {
            sig_atomic_t received[NSIG];
            int sig;
  
            for (sig = 0; sig < NSIG; sig++)
              if ((to_unblock >> sig) & 1)
                {
                  if (signal (sig, old_handlers[sig]) != blocked_handler)
                    /* The application changed a signal handler while the signal
                       was blocked, bypassing our rpl_signal replacement.
                       We don't support this.  */
                    abort ();
                  received[sig] = pending_array[sig];
                  blocked_set &= ~(1U << sig);
                  pending_array[sig] = 0;
                }
              else
                received[sig] = 0;
  
            for (sig = 0; sig < NSIG; sig++)
              if (received[sig])
                raise (sig);
          }
      }
    return 0;
  }
  
  /* Install the handler FUNC for signal SIG, and return the previous
     handler.  */
  handler_t
  rpl_signal (int sig, handler_t handler)
  {
    /* We must provide a wrapper, so that a user can query what handler
       they installed even if that signal is currently blocked.  */
    if (sig >= 0 && sig < NSIG && sig != SIGKILL && sig != SIGSTOP
        && handler != SIG_ERR)
      {
        #ifdef SIGABRT_COMPAT
        if (sig == SIGABRT_COMPAT)
          sig = SIGABRT;
        #endif
  
        if (blocked_set & (1U << sig))
          {
            /* POSIX states that sigprocmask and signal are both
               async-signal-safe.  This is not true of our
               implementation - there is a slight data race where an
               asynchronous interrupt on signal A can occur after we
               install blocked_handler but before we have updated
               old_handlers for signal B, such that handler A can see
               stale information if it calls signal(B).  Oh well -
               signal handlers really shouldn't try to manipulate the
               installed handlers of unrelated signals.  */
            handler_t result = old_handlers[sig];
            old_handlers[sig] = handler;
            return result;
          }
        else
          return signal (sig, handler);
      }
    else
      {
        errno = EINVAL;
        return SIG_ERR;
      }
  }
  
  #if GNULIB_defined_SIGPIPE
  /* Raise the signal SIGPIPE.  */
  int
  _gl_raise_SIGPIPE (void)
  {
    if (blocked_set & (1U << SIGPIPE))
      pending_array[SIGPIPE] = 1;
    else
      {
        handler_t handler = SIGPIPE_handler;
        if (handler == SIG_DFL)
          exit (128 + SIGPIPE);
        else if (handler != SIG_IGN)
          (*handler) (SIGPIPE);
      }
    return 0;
  }
  #endif
  