gdbsupport/scoped_ignore_signal.h

/* Support for ignoring signals.

   Copyright (C) 2021 Free Software Foundation, Inc.

   This file is part of GDB.

   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 <http://www.gnu.org/licenses/>.  */

#ifndef SCOPED_IGNORE_SIGNAL_H
#define SCOPED_IGNORE_SIGNAL_H

#include <signal.h>

/* RAII class used to ignore a signal in a scope.  If sigprocmask is
   supported, then the signal is only ignored by the calling thread.
   Otherwise, the signal disposition is set to SIG_IGN, which affects
   the whole process.  */

template <int Sig>
class scoped_ignore_signal
{
public:
  scoped_ignore_signal ()
  {
#ifdef HAVE_SIGPROCMASK
    sigset_t set, old_state;

    sigemptyset (&set);
    sigaddset (&set, Sig);
    sigprocmask (SIG_BLOCK, &set, &old_state);
    m_was_blocked = sigismember (&old_state, Sig);
#else
    m_osig = signal (Sig, SIG_IGN);
#endif
  }

  ~scoped_ignore_signal ()
  {
#ifdef HAVE_SIGPROCMASK
    if (!m_was_blocked)
      {
	sigset_t set;
	const timespec zero_timeout = {};

	sigemptyset (&set);
	sigaddset (&set, Sig);

	/* If we got a pending Sig signal, consume it before
	   unblocking.  */
	sigtimedwait (&set, nullptr, &zero_timeout);

	sigprocmask (SIG_UNBLOCK, &set, nullptr);
      }
#else
    signal (Sig, m_osig);
#endif
  }

  DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal);

private:
#ifdef HAVE_SIGPROCMASK
  bool m_was_blocked;
#else
  sighandler_t m_osig;
#endif
};

struct scoped_ignore_signal_nop
{
  /* Note, these can't both be "= default", because otherwise the
     compiler warns that variables of this type are not used.  */
  scoped_ignore_signal_nop ()
  {}
  ~scoped_ignore_signal_nop ()
  {}
  DISABLE_COPY_AND_ASSIGN (scoped_ignore_signal_nop);
};

#ifdef SIGPIPE
using scoped_ignore_sigpipe = scoped_ignore_signal<SIGPIPE>;
#else
using scoped_ignore_sigpipe = scoped_ignore_signal_nop;
#endif

#endif /* SCOPED_IGNORE_SIGNAL_H */