#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:
- CrossThreadChannel();
+ /** 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();
- int selectable() const { return fds[0]; }
+
+ /* 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),
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];
+ int fds[2]; // current implementation uses a pipe/fifo
};
#endif /* __pbd__crossthread_h__ */