2 Copyright (C) 2000-2007 Paul Davis
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2 of the License, or
7 (at your option) any later version.
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License
15 along with this program; if not, write to the Free Software
16 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 #ifndef __pbd__crossthread_h__
21 #define __pbd__crossthread_h__
27 #include <glibmm/main.h>
29 #include "pbd/libpbd_visibility.h"
31 /** A simple abstraction of a mechanism of signalling one thread from another.
32 * The signaller calls ::wakeup() to tell the signalled thread to check for
35 * This implementation provides both ::selectable() for use in direct
36 * poll/select-based event loops, and a Glib::IOSource via ::ios() for use
37 * in Glib main loop based situations.
40 class LIBPBD_API CrossThreadChannel {
42 /** if @a non_blocking is true, the channel will not cause blocking
43 * when used in an event loop based on poll/select or the glib main
46 CrossThreadChannel(bool non_blocking);
47 ~CrossThreadChannel();
49 /** Tell the listening thread that is has work to do.
53 /* if the listening thread cares about the precise message
54 * it is being sent, then ::deliver() can be used to send
55 * a single byte message rather than a simple wakeup. These
56 * two mechanisms should not be used on the same CrossThreadChannel
57 * because there is no way to know which byte value will be used
60 int deliver (char msg);
62 /** if using ::deliver() to wakeup the listening thread, then
63 * the listener should call ::receive() to fetch the message
64 * type from the channel.
66 int receive (char& msg);
68 /** empty the channel of all requests.
69 * Typically this is done as soon as input
70 * is noticed on the channel, because the
71 * handler will look at a separately managed work
72 * queue. The actual number of queued "wakeups"
73 * in the channel will not be important.
76 static void drain (int fd);
78 /** File descriptor that can be used with poll/select to
79 * detect when wakeup() has been called on this channel.
80 * It be marked as readable/input-ready when this condition
81 * is true. It has already been marked non-blocking.
83 int selectable() const { return fds[0]; }
85 /* glibmm 2.22 and earlier has a terrifying bug that will
86 cause crashes whenever a Source is removed from
87 a MainContext (including the destruction of the MainContext),
88 because the Source is destroyed "out from under the nose of"
89 the RefPtr. I (Paul) have fixed this (https://bugzilla.gnome.org/show_bug.cgi?id=561885)
90 but in the meantime, we need a hack to get around the issue.
92 Glib::RefPtr<Glib::IOSource> ios();
95 /** returns true if the CrossThreadChannel was
96 * correctly constructed.
98 bool ok() const { return fds[0] >= 0 && fds[1] >= 0; }
101 Glib::RefPtr<Glib::IOSource>* _ios; // lazily constructed
102 int fds[2]; // current implementation uses a pipe/fifo
105 #endif /* __pbd__crossthread_h__ */