src/xz/signals.c

///////////////////////////////////////////////////////////////////////////////
//
/// \file       signals.c
/// \brief      Handling signals to abort operation
//
//  Author:     Lasse Collin
//
//  This file has been put into the public domain.
//  You can do whatever you want with this file.
//
///////////////////////////////////////////////////////////////////////////////

#include "private.h"


volatile sig_atomic_t user_abort = false;


#ifndef _WIN32

/// If we were interrupted by a signal, we store the signal number so that
/// we can raise that signal to kill the program when all cleanups have
/// been done.
static volatile sig_atomic_t exit_signal = 0;

/// Mask of signals for which have have established a signal handler to set
/// user_abort to true.
static sigset_t hooked_signals;

/// signals_block() and signals_unblock() can be called recursively.
static size_t signals_block_count = 0;


static void
signal_handler(int sig)
{
	exit_signal = sig;
	user_abort = true;
	return;
}


extern void
signals_init(void)
{
	// List of signals for which we establish the signal handler.
	static const int sigs[] = {
		SIGINT,
		SIGTERM,
#ifdef SIGHUP
		SIGHUP,
#endif
#ifdef SIGPIPE
		SIGPIPE,
#endif
#ifdef SIGXCPU
		SIGXCPU,
#endif
#ifdef SIGXFSZ
		SIGXFSZ,
#endif
	};

	// Mask of the signals for which we have established a signal handler.
	sigemptyset(&hooked_signals);
	for (size_t i = 0; i < ARRAY_SIZE(sigs); ++i)
		sigaddset(&hooked_signals, sigs[i]);

	struct sigaction sa;

	// All the signals that we handle we also blocked while the signal
	// handler runs.
	sa.sa_mask = hooked_signals;

	// Don't set SA_RESTART, because we want EINTR so that we can check
	// for user_abort and cleanup before exiting. We block the signals
	// for which we have established a handler when we don't want EINTR.
	sa.sa_flags = 0;
	sa.sa_handler = &signal_handler;

	for (size_t i = 0; i < ARRAY_SIZE(sigs); ++i) {
		// If the parent process has left some signals ignored,
		// we don't unignore them.
		struct sigaction old;
		if (sigaction(sigs[i], NULL, &old) == 0
				&& old.sa_handler == SIG_IGN)
			continue;

		// Establish the signal handler.
		if (sigaction(sigs[i], &sa, NULL))
			message_signal_handler();
	}

	return;
}


extern void
signals_block(void)
{
	if (signals_block_count++ == 0) {
		const int saved_errno = errno;
		mythread_sigmask(SIG_BLOCK, &hooked_signals, NULL);
		errno = saved_errno;
	}

	return;
}


extern void
signals_unblock(void)
{
	assert(signals_block_count > 0);

	if (--signals_block_count == 0) {
		const int saved_errno = errno;
		mythread_sigmask(SIG_UNBLOCK, &hooked_signals, NULL);
		errno = saved_errno;
	}

	return;
}


extern void
signals_exit(void)
{
	const int sig = exit_signal;

	if (sig != 0) {
		struct sigaction sa;
		sa.sa_handler = SIG_DFL;
		sigfillset(&sa.sa_mask);
		sa.sa_flags = 0;
		sigaction(sig, &sa, NULL);
		raise(exit_signal);
	}

	return;
}

#else

// While Windows has some very basic signal handling functions as required
// by C89, they are not really used, or so I understood. Instead, we use
// SetConsoleCtrlHandler() to catch user pressing C-c.

#include <windows.h>


static BOOL WINAPI
signal_handler(DWORD type lzma_attribute((unused)))
{
	// Since we don't get a signal number which we could raise() at
	// signals_exit() like on POSIX, just set the exit status to
	// indicate an error, so that we cannot return with zero exit status.
	set_exit_status(E_ERROR);
	user_abort = true;
	return TRUE;
}


extern void
signals_init(void)
{
	if (!SetConsoleCtrlHandler(&signal_handler, TRUE))
		message_signal_handler();

	return;
}

#endif