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/*
Copyright (C) 2000-2007 Paul Davis
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 2 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, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifndef __pbd__crossthread_h__
#define __pbd__crossthread_h__
#ifdef check
#undef check
#endif
#include <glibmm/main.h>
/** A simple abstraction of a mechanism of signalling one thread from another.
* The signaller calls ::wakeup() to tell the signalled thread to check for
* work to be done.
*
* This implementation provides both ::selectable() for use in direct
* poll/select-based event loops, and a Glib::IOSource via ::ios() for use
* in Glib main loop based situations.
*/
class CrossThreadChannel {
public:
/** if @a non_blocking is true, the channel will not cause blocking
* when used in an event loop based on poll/select or the glib main
* loop.
*/
CrossThreadChannel(bool non_blocking);
~CrossThreadChannel();
/** Tell the listening thread that is has work to do.
*/
void wakeup();
/* if the listening thread cares about the precise message
* it is being sent, then ::deliver() can be used to send
* a single byte message rather than a simple wakeup. These
* two mechanisms should not be used on the same CrossThreadChannel
* because there is no way to know which byte value will be used
* for ::wakeup()
*/
int deliver (char msg);
/** if using ::deliver() to wakeup the listening thread, then
* the listener should call ::receive() to fetch the message
* type from the channel.
*/
int receive (char& msg);
/** empty the channel of all requests.
* Typically this is done as soon as input
* is noticed on the channel, because the
* handler will look at a separately managed work
* queue. The actual number of queued "wakeups"
* in the channel will not be important.
*/
void drain ();
static void drain (int fd);
/** File descriptor that can be used with poll/select to
* detect when wakeup() has been called on this channel.
* It be marked as readable/input-ready when this condition
* is true. It has already been marked non-blocking.
*/
int selectable() const { return fds[0]; }
/* glibmm 2.22 and earlier has a terrifying bug that will
cause crashes whenever a Source is removed from
a MainContext (including the destruction of the MainContext),
because the Source is destroyed "out from under the nose of"
the RefPtr. I (Paul) have fixed this (https://bugzilla.gnome.org/show_bug.cgi?id=561885)
but in the meantime, we need a hack to get around the issue.
*/
Glib::RefPtr<Glib::IOSource> ios();
void drop_ios ();
/** returns true if the CrossThreadChannel was
* correctly constructed.
*/
bool ok() const { return fds[0] >= 0 && fds[1] >= 0; }
private:
Glib::RefPtr<Glib::IOSource>* _ios; // lazily constructed
int fds[2]; // current implementation uses a pipe/fifo
};
#endif /* __pbd__crossthread_h__ */
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