myxlib/src/myx/qt/posix_signal_watcher.cpp

#ifndef MYX_QT_POSIX_SIGNAL_WATCHER_CPP_
#define MYX_QT_POSIX_SIGNAL_WATCHER_CPP_

#include <myx/base/config.hpp>

#ifndef MYXLIB_HEADER_ONLY
#include <myx/qt/posix_signal_watcher_p.hpp>
#include <myx/qt/posix_signal_watcher.hpp>
#else
#pragma once
#endif


namespace myx {

namespace qt {

int PosixSignalWatcherPrivate::m_sockpair[2] = {0, 0};

PosixSignalWatcherPrivate::~PosixSignalWatcherPrivate() = default;

PosixSignalWatcherPrivate::PosixSignalWatcherPrivate( PosixSignalWatcher* q ) :
	q_ptr( q )
{
	#if MYX_QT_HAS_POSIX_SIGNALS
	// Create socket pair
	if ( ::socketpair( AF_UNIX, SOCK_STREAM, 0, m_sockpair ) )
	{
		qDebug() << "PosixSignalWatcher: socketpair: " << ::strerror( errno );
		return;
	}
	#endif

	// Create a notifier for the read end of the pair
	m_notifier.reset( new QSocketNotifier( m_sockpair[1], QSocketNotifier::Read ) );


	// Called when the signal handler has written to the socket pair.
	// Emits the Posix signal as a Qt signal.
	connect( m_notifier.get(), &QSocketNotifier::activated, q, [this]( int sockfd ) {
		Q_Q( PosixSignalWatcher );

		int signal = 0;
		(void)::read( sockfd, &signal, sizeof( signal ) );
		qDebug() << "Caught signal: " << ::strsignal( signal );
		Q_EMIT q->posixSignal( signal );
	} );


	m_notifier->setEnabled( true );
}


/*!
 * Registers a handler for the given Posix \a signal. The handler will write to
 * a socket pair, the other end of which is connected to a QSocketNotifier.
 * This provides a way to break out of the asynchronous context from which the
 * signal handler is called and back into the Qt event loop.
 */
void PosixSignalWatcherPrivate::watchForSignal( int signal )
{
	if ( m_watchedSignals.contains( signal ) )
	{
		qDebug() << "Already watching for signal " << signal;
		return;
	}

	#if MYX_QT_HAS_POSIX_SIGNALS
	// Register a sigaction which will write to the socket pair
	struct sigaction sigact;
	sigact.sa_handler = PosixSignalWatcherPrivate::signalHandler;
	sigact.sa_flags   = 0;
	sigemptyset( &sigact.sa_mask );
	sigact.sa_flags |= SA_RESTART;
	if ( ::sigaction( signal, &sigact, nullptr ) )
	{
		qDebug() << "PosixSignalWatcher: sigaction: " << ::strerror( errno );
		return;
	}
	#endif

	m_watchedSignals.append( signal );
} // PosixSignalWatcherPrivate::watchForSignal


/*!
 * Called when a Posix \a signal is received. Write to the socket to wake up the
 * QSocketNotifier.
 */
MYXLIB_INLINE void PosixSignalWatcherPrivate::signalHandler( int signal )
{
	(void)::write( m_sockpair[0], &signal, sizeof( signal ) );
}


/*!
 * Create a new PosixSignalWatcher as a child of the given \a parent.
 */
MYXLIB_INLINE PosixSignalWatcher::PosixSignalWatcher( QObject* parent ) :
	QObject( parent ),
	d_ptr  ( new PosixSignalWatcherPrivate( this ) )
{
}


MYXLIB_INLINE PosixSignalWatcher::~PosixSignalWatcher() = default;

/*!
 * Register a signal handler for the given \a signal.
 *
 * After calling this method you can \c connect() to the POSIXSignal() Qt signal
 * to be notified when the Posix signal is received.
 */
MYXLIB_INLINE void PosixSignalWatcher::watchForSignal( int signal )
{
	Q_D( PosixSignalWatcher );
	d->watchForSignal( signal );
}


/*!
 * \fn void PosixSignalWatcher::posixSignal(int signal)
 * Emitted when the given Posix \a signal is received.
 *
 * watchForSignal() must be called for each Posix signal that you want to receive
 * via the POSIXSignal() Qt signal. If a watcher is watching multiple signals,
 * POSIXSignal() will be emitted whenever *any* of the watched Posix signals are
 * received, and the \a signal argument can be inspected to find out which one
 * was actually received.
 */

} // namespace qt

} // namespace myx

#endif // ifndef MYX_QT_POSIX_SIGNAL_WATCHER_CPP_