Merge branch 'noppc' of https://github.com/mojofunk/ardour into cairocanvas

[ardour.git] / libs / pbd / pbd / crossthread.h

diff --git a/libs/pbd/pbd/crossthread.h b/libs/pbd/pbd/crossthread.h
index f9845eedf07fa115427ec420fe6fa9fb0051db03..d172c9c60f65933df348e3130ab8ea74210b5d75 100644 (file)
--- a/libs/pbd/pbd/crossthread.h
+++ b/libs/pbd/pbd/crossthread.h
@@ -20,22 +20,68 @@
 #ifndef __pbd__crossthread_h__
 #define __pbd__crossthread_h__
 
+#ifdef check
+#undef check
+#endif
+
 #include <glibmm/main.h>
 
-class CrossThreadChannel { 
+#include "pbd/libpbd_visibility.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 LIBPBD_API 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),
@@ -43,15 +89,17 @@ class CrossThreadChannel {
           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__ */