initial commit, 4.5 stable

thirdparty/linuxbsd_headers/pulse/thread-mainloop.h

@@ -0,0 +1,317 @@
+#ifndef foothreadmainloophfoo
+#define foothreadmainloophfoo
+
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2006 Lennart Poettering
+  Copyright 2006 Pierre Ossman <ossman@cendio.se> for Cendio AB
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as published
+  by the Free Software Foundation; either version 2.1 of the License,
+  or (at your option) any later version.
+
+  PulseAudio 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 Lesser General Public License
+  along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <pulse/mainloop-api.h>
+#include <pulse/cdecl.h>
+#include <pulse/version.h>
+
+PA_C_DECL_BEGIN
+
+/** \page threaded_mainloop Threaded Main Loop
+ *
+ * \section overv_sec Overview
+ *
+ * The threaded main loop implementation is a special version of the primary
+ * main loop implementation (see \ref mainloop). For the basic design, see
+ * its documentation.
+ *
+ * The added feature in the threaded main loop is that it spawns a new thread
+ * that runs the real main loop. This allows a synchronous application to use
+ * the asynchronous API without risking to stall the PulseAudio library.
+ *
+ * \section creat_sec Creation
+ *
+ * A pa_threaded_mainloop object is created using pa_threaded_mainloop_new().
+ * This will only allocate the required structures though, so to use it the
+ * thread must also be started. This is done through
+ * pa_threaded_mainloop_start(), after which you can start using the main loop.
+ *
+ * \section destr_sec Destruction
+ *
+ * When the PulseAudio connection has been terminated, the thread must be
+ * stopped and the resources freed. Stopping the thread is done using
+ * pa_threaded_mainloop_stop(), which must be called without the lock (see
+ * below) held. When that function returns, the thread is stopped and the
+ * pa_threaded_mainloop object can be freed using pa_threaded_mainloop_free().
+ *
+ * \section lock_sec Locking
+ *
+ * Since the PulseAudio API doesn't allow concurrent accesses to objects,
+ * a locking scheme must be used to guarantee safe usage. The threaded main
+ * loop API provides such a scheme through the functions
+ * pa_threaded_mainloop_lock() and pa_threaded_mainloop_unlock().
+ *
+ * The lock is recursive, so it's safe to use it multiple times from the same
+ * thread. Just make sure you call pa_threaded_mainloop_unlock() the same
+ * number of times you called pa_threaded_mainloop_lock().
+ *
+ * The lock needs to be held whenever you call any PulseAudio function that
+ * uses an object associated with this main loop. Make sure you do not hold
+ * on to the lock more than necessary though, as the threaded main loop stops
+ * while the lock is held.
+ *
+ * Example:
+ *
+ * \code
+ * void my_check_stream_func(pa_threaded_mainloop *m, pa_stream *s) {
+ *     pa_stream_state_t state;
+ *
+ *     pa_threaded_mainloop_lock(m);
+ *
+ *     state = pa_stream_get_state(s);
+ *
+ *     pa_threaded_mainloop_unlock(m);
+ *
+ *     if (state == PA_STREAM_READY)
+ *         printf("Stream is ready!");
+ *     else
+ *         printf("Stream is not ready!");
+ * }
+ * \endcode
+ *
+ * \section cb_sec Callbacks
+ *
+ * Callbacks in PulseAudio are asynchronous, so they require extra care when
+ * using them together with a threaded main loop.
+ *
+ * The easiest way to turn the callback based operations into synchronous
+ * ones, is to simply wait for the callback to be called and continue from
+ * there. This is the approach chosen in PulseAudio's threaded API.
+ *
+ * \subsection basic_subsec Basic callbacks
+ *
+ * For the basic case, where all that is required is to wait for the callback
+ * to be invoked, the code should look something like this:
+ *
+ * Example:
+ *
+ * \code
+ * static void my_drain_callback(pa_stream *s, int success, void *userdata) {
+ *     pa_threaded_mainloop *m;
+ *
+ *     m = userdata;
+ *     assert(m);
+ *
+ *     pa_threaded_mainloop_signal(m, 0);
+ * }
+ *
+ * void my_drain_stream_func(pa_threaded_mainloop *m, pa_stream *s) {
+ *     pa_operation *o;
+ *
+ *     pa_threaded_mainloop_lock(m);
+ *
+ *     o = pa_stream_drain(s, my_drain_callback, m);
+ *     assert(o);
+ *
+ *     while (pa_operation_get_state(o) == PA_OPERATION_RUNNING)
+ *         pa_threaded_mainloop_wait(m);
+ *
+ *     pa_operation_unref(o);
+ *
+ *     pa_threaded_mainloop_unlock(m);
+ * }
+ * \endcode
+ *
+ * The main function, my_drain_stream_func(), will wait for the callback to
+ * be called using pa_threaded_mainloop_wait().
+ *
+ * If your application is multi-threaded, then this waiting must be
+ * done inside a while loop. The reason for this is that multiple
+ * threads might be using pa_threaded_mainloop_wait() at the same
+ * time. Each thread must therefore verify that it was its callback
+ * that was invoked. Also the underlying OS synchronization primitives
+ * are usually not free of spurious wake-ups, so a
+ * pa_threaded_mainloop_wait() must be called within a loop even if
+ * you have only one thread waiting.
+ *
+ * The callback, my_drain_callback(), indicates to the main function that it
+ * has been called using pa_threaded_mainloop_signal().
+ *
+ * As you can see, pa_threaded_mainloop_wait() may only be called with
+ * the lock held. The same thing is true for pa_threaded_mainloop_signal(),
+ * but as the lock is held before the callback is invoked, you do not have to
+ * deal with that.
+ *
+ * The functions will not dead lock because the wait function will release
+ * the lock before waiting and then regrab it once it has been signalled.
+ * For those of you familiar with threads, the behaviour is that of a
+ * condition variable.
+ *
+ * \subsection data_subsec Data callbacks
+ *
+ * For many callbacks, simply knowing that they have been called is
+ * insufficient. The callback also receives some data that is desired. To
+ * access this data safely, we must extend our example a bit:
+ *
+ * \code
+ * static int * volatile drain_result = NULL;
+ *
+ * static void my_drain_callback(pa_stream*s, int success, void *userdata) {
+ *     pa_threaded_mainloop *m;
+ *
+ *     m = userdata;
+ *     assert(m);
+ *
+ *     drain_result = &success;
+ *
+ *     pa_threaded_mainloop_signal(m, 1);
+ * }
+ *
+ * void my_drain_stream_func(pa_threaded_mainloop *m, pa_stream *s) {
+ *     pa_operation *o;
+ *
+ *     pa_threaded_mainloop_lock(m);
+ *
+ *     o = pa_stream_drain(s, my_drain_callback, m);
+ *     assert(o);
+ *
+ *     while (drain_result == NULL)
+ *         pa_threaded_mainloop_wait(m);
+ *
+ *     pa_operation_unref(o);
+ *
+ *     if (*drain_result)
+ *         printf("Success!");
+ *     else
+ *         printf("Bitter defeat...");
+ *
+ *     pa_threaded_mainloop_accept(m);
+ *
+ *     pa_threaded_mainloop_unlock(m);
+ * }
+ * \endcode
+ *
+ * The example is a bit silly as it would probably have been easier to just
+ * copy the contents of success, but for larger data structures this can be
+ * wasteful.
+ *
+ * The difference here compared to the basic callback is the value 1 passed
+ * to pa_threaded_mainloop_signal() and the call to
+ * pa_threaded_mainloop_accept(). What will happen is that
+ * pa_threaded_mainloop_signal() will signal the main function and then wait.
+ * The main function is then free to use the data in the callback until
+ * pa_threaded_mainloop_accept() is called, which will allow the callback
+ * to continue.
+ *
+ * Note that pa_threaded_mainloop_accept() must be called some time between
+ * exiting the while loop and unlocking the main loop! Failure to do so will
+ * result in a race condition. I.e. it is not ok to release the lock and
+ * regrab it before calling pa_threaded_mainloop_accept().
+ *
+ * \subsection async_subsec Asynchronous callbacks
+ *
+ * PulseAudio also has callbacks that are completely asynchronous, meaning
+ * that they can be called at any time. The threaded main loop API provides
+ * the locking mechanism to handle concurrent accesses, but nothing else.
+ * Applications will have to handle communication from the callback to the
+ * main program through their own mechanisms.
+ *
+ * The callbacks that are completely asynchronous are:
+ *
+ * \li State callbacks for contexts, streams, etc.
+ * \li Subscription notifications
+ */
+
+/** \file
+ *
+ * A thread based event loop implementation based on pa_mainloop. The
+ * event loop is run in a helper thread in the background. A few
+ * synchronization primitives are available to access the objects
+ * attached to the event loop safely.
+ *
+ * See also \subpage threaded_mainloop
+ */
+
+/** An opaque threaded main loop object */
+typedef struct pa_threaded_mainloop pa_threaded_mainloop;
+
+/** Allocate a new threaded main loop object. You have to call
+ * pa_threaded_mainloop_start() before the event loop thread starts
+ * running. */
+pa_threaded_mainloop *pa_threaded_mainloop_new(void);
+
+/** Free a threaded main loop object. If the event loop thread is
+ * still running, terminate it with pa_threaded_mainloop_stop()
+ * first. */
+void pa_threaded_mainloop_free(pa_threaded_mainloop* m);
+
+/** Start the event loop thread. */
+int pa_threaded_mainloop_start(pa_threaded_mainloop *m);
+
+/** Terminate the event loop thread cleanly. Make sure to unlock the
+ * mainloop object before calling this function. */
+void pa_threaded_mainloop_stop(pa_threaded_mainloop *m);
+
+/** Lock the event loop object, effectively blocking the event loop
+ * thread from processing events. You can use this to enforce
+ * exclusive access to all objects attached to the event loop. This
+ * lock is recursive. This function may not be called inside the event
+ * loop thread. Events that are dispatched from the event loop thread
+ * are executed with this lock held. */
+void pa_threaded_mainloop_lock(pa_threaded_mainloop *m);
+
+/** Unlock the event loop object, inverse of pa_threaded_mainloop_lock(). */
+void pa_threaded_mainloop_unlock(pa_threaded_mainloop *m);
+
+/** Wait for an event to be signalled by the event loop thread. You
+ * can use this to pass data from the event loop thread to the main
+ * thread in a synchronized fashion. This function may not be called
+ * inside the event loop thread. Prior to this call the event loop
+ * object needs to be locked using pa_threaded_mainloop_lock(). While
+ * waiting the lock will be released. Immediately before returning it
+ * will be acquired again. This function may spuriously wake up even
+ * without pa_threaded_mainloop_signal() being called. You need to
+ * make sure to handle that! */
+void pa_threaded_mainloop_wait(pa_threaded_mainloop *m);
+
+/** Signal all threads waiting for a signalling event in
+ * pa_threaded_mainloop_wait(). If wait_for_accept is non-zero, do
+ * not return before the signal was accepted by a
+ * pa_threaded_mainloop_accept() call. While waiting for that condition
+ * the event loop object is unlocked. */
+void pa_threaded_mainloop_signal(pa_threaded_mainloop *m, int wait_for_accept);
+
+/** Accept a signal from the event thread issued with
+ * pa_threaded_mainloop_signal(). This call should only be used in
+ * conjunction with pa_threaded_mainloop_signal() with a non-zero
+ * wait_for_accept value.  */
+void pa_threaded_mainloop_accept(pa_threaded_mainloop *m);
+
+/** Return the return value as specified with the main loop's
+ * pa_mainloop_quit() routine. */
+int pa_threaded_mainloop_get_retval(pa_threaded_mainloop *m);
+
+/** Return the main loop abstraction layer vtable for this main loop.
+ * There is no need to free this object as it is owned by the loop
+ * and is destroyed when the loop is freed. */
+pa_mainloop_api* pa_threaded_mainloop_get_api(pa_threaded_mainloop*m);
+
+/** Returns non-zero when called from within the event loop thread. \since 0.9.7 */
+int pa_threaded_mainloop_in_thread(pa_threaded_mainloop *m);
+
+/** Sets the name of the thread. \since 5.0 */
+void pa_threaded_mainloop_set_name(pa_threaded_mainloop *m, const char *name);
+
+PA_C_DECL_END
+
+#endif