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 /** A simple abstraction of a mechanism of signalling one thread from another.
30 * The signaller calls ::wakeup() to tell the signalled thread to check for
33 * This implementation provides both ::selectable() for use in direct
34 * poll/select-based event loops, and a Glib::IOSource via ::ios() for use
35 * in Glib main loop based situations.
38 class CrossThreadChannel {
40 /** if @a non_blocking is true, the channel will not cause blocking
41 * when used in an event loop based on poll/select or the glib main
44 CrossThreadChannel(bool non_blocking);
45 ~CrossThreadChannel();
47 /** Tell the listening thread that is has work to do.
51 /* if the listening thread cares about the precise message
52 * it is being sent, then ::deliver() can be used to send
53 * a single byte message rather than a simple wakeup. These
54 * two mechanisms should not be used on the same CrossThreadChannel
55 * because there is no way to know which byte value will be used
58 int deliver (char msg);
60 /** if using ::deliver() to wakeup the listening thread, then
61 * the listener should call ::receive() to fetch the message
62 * type from the channel.
64 int receive (char& msg);
66 /** empty the channel of all requests.
67 * Typically this is done as soon as input
68 * is noticed on the channel, because the
69 * handler will look at a separately managed work
70 * queue. The actual number of queued "wakeups"
71 * in the channel will not be important.
74 static void drain (int fd);
76 /** File descriptor that can be used with poll/select to
77 * detect when wakeup() has been called on this channel.
78 * It be marked as readable/input-ready when this condition
79 * is true. It has already been marked non-blocking.
81 int selectable() const { return fds[0]; }
83 /* glibmm 2.22 and earlier has a terrifying bug that will
84 cause crashes whenever a Source is removed from
85 a MainContext (including the destruction of the MainContext),
86 because the Source is destroyed "out from under the nose of"
87 the RefPtr. I (Paul) have fixed this (https://bugzilla.gnome.org/show_bug.cgi?id=561885)
88 but in the meantime, we need a hack to get around the issue.
90 Glib::RefPtr<Glib::IOSource> ios();
93 /** returns true if the CrossThreadChannel was
94 * correctly constructed.
96 bool ok() const { return fds[0] >= 0 && fds[1] >= 0; }
99 Glib::RefPtr<Glib::IOSource>* _ios; // lazily constructed
100 int fds[2]; // current implementation uses a pipe/fifo
103 #endif /* __pbd__crossthread_h__ */