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docs: add tutorial 3
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@ -6,3 +6,5 @@ PipeWire API step-by-step with simple short examples.
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1) Getting started ([tutorial 1](tutorial1.md)).
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2) Enumerating objects ([tutorial 2](tutorial2.md)).
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3) Forcing a roundtrip ([tutorial 3](tutorial3.md)).
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@ -59,11 +59,11 @@ int main(int argc, char *argv[])
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}
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```
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To compile the simple test application, copy it into a test2.c file and
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To compile the simple test application, copy it into a tutorial2.c file and
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use:
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```
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gcc -Wall test2.c -o test2 $(pkg-config --cflags --libs libpipewire-0.3)
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gcc -Wall tutorial2.c -o tutorial2 $(pkg-config --cflags --libs libpipewire-0.3)
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```
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Let's break this down:
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210
doc/tutorial3.md
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210
doc/tutorial3.md
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@ -0,0 +1,210 @@
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[previous](tutorial2.md) [index](tutorial-index.md) [next](tutorial4.md)
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# Forcing a roundtrip (Tutorial 3)
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In this tutorial we show how to force a roundtrip to the server
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to make sure an action completed.
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We'll change our example from [Tutorial 2](tutorial2.md) slightly
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and add the extra code to implement the roundtrip.
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Let's take the following small method first:
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```c
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static int roundtrip(struct pw_core *core, struct pw_main_loop *loop)
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{
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struct spa_hook core_listener;
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int pending, done = 0;
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void core_event_done(void *object, uint32_t id, int seq) {
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if (id == PW_ID_CORE && seq == pending) {
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done = 1;
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pw_main_loop_quit(loop);
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}
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}
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const struct pw_core_events core_events = {
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PW_VERSION_CORE_EVENTS,
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.done = core_event_done,
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};
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spa_zero(core_listener);
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pw_core_add_listener(core, &core_listener,
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&core_events, NULL);
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pending = pw_core_sync(core, PW_ID_CORE, 0);
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while (!done) {
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pw_main_loop_run(loop);
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}
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spa_hook_remove(&core_listener);
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return 0;
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}
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```
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Let's take a look at what this method does.
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```c
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struct spa_hook core_listener;
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spa_zero(core_listener);
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pw_core_add_listener(core, &core_listener,
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&core_events, NULL);
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```
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First of all we add a listener for the events of the core
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object. We are only interested in the `done` event in this
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tutorial. This is the event handler:
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```c
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int pending, done = 0;
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void core_event_done(void *object, uint32_t id, int seq) {
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if (id == PW_ID_CORE && seq == pending) {
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done = 1;
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pw_main_loop_quit(loop);
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}
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}
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const struct pw_core_events core_events = {
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PW_VERSION_CORE_EVENTS,
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.done = core_event_done,
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};
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```
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When the done event is received for an object with id `PW_ID_CORE`
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and a certain sequence number `seq`, this function will set the done
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variable to 1 and call `pw_main_loop_quit()`.
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Next we do:
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```c
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pending = pw_core_sync(core, PW_ID_CORE, 0);
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```
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This triggers the `sync` method on the core object with id
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`PW_ID_CORE` and sequence number 0.
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Because this is a method on a proxy object, it will be executed
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asynchronously and the returns value will reflect this. PipeWire
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uses the return values of the underlying SPA (Simple Plugin API)
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helper objects (See also [error codes](spa/design.md#error-codes).
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Because all messages on the PipeWire server are handled sequencially,
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the sync method will be executed after all previous methods are
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completed. The PipeWire server will emit a `done` event with the
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same ID and the return value of the original `pw_core_sync()`
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method in the sequence number.
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We then run the mainloop to send the messages to the server and
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receive the events:
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```c
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while (!done) {
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pw_main_loop_run(loop);
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}
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```
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When we get the done event, we can compare it to the sync method
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and then we know that we did a complete roundtrip and there are no
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more pending methods on the server. We can quit the mainloop and
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remove the listener:
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```c
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spa_hook_remove(&core_listener);
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return 0;
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}
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```
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If we add this roundtrip method to our code and call it instead of the
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`pw_main_loop_run()` we will exit the program after all previous methods
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are finished. This means that the `pw_core_get_registry()` call
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completed and thus that we also received all events for the globals
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on the server.
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```c
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#include <pipewire/pipewire.h>
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static int roundtrip(struct pw_core *core, struct pw_main_loop *loop)
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{
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struct spa_hook core_listener;
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int pending, done = 0;
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void core_event_done(void *object, uint32_t id, int seq) {
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if (id == PW_ID_CORE && seq == pending) {
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done = 1;
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pw_main_loop_quit(loop);
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}
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}
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const struct pw_core_events core_events = {
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PW_VERSION_CORE_EVENTS,
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.done = core_event_done,
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};
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spa_zero(core_listener);
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pw_core_add_listener(core, &core_listener,
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&core_events, NULL);
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pending = pw_core_sync(core, PW_ID_CORE, 0);
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while (!done) {
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pw_main_loop_run(loop);
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}
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spa_hook_remove(&core_listener);
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return 0;
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}
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static void registry_event_global(void *data, uint32_t id,
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uint32_t permissions, const char *type, uint32_t version,
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const struct spa_dict *props)
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{
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printf("object: id:%u type:%s/%d\n", id, type, version);
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}
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static const struct pw_registry_events registry_events = {
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PW_VERSION_REGISTRY_EVENTS,
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.global = registry_event_global,
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};
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int main(int argc, char *argv[])
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{
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struct pw_main_loop *loop;
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struct pw_context *context;
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struct pw_core *core;
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struct pw_registry *registry;
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struct spa_hook registry_listener;
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pw_init(&argc, &argv);
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loop = pw_main_loop_new(NULL /* properties */);
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context = pw_context_new(pw_main_loop_get_loop(loop),
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NULL /* properties */,
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0 /* user_data size */);
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core = pw_context_connect(context,
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NULL /* properties */,
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0 /* user_data size */);
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registry = pw_core_get_registry(core, PW_VERSION_REGISTRY,
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0 /* user_data size */);
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spa_zero(registry_listener);
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pw_registry_add_listener(registry, ®istry_listener,
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®istry_events, NULL);
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roundtrip(core, loop);
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pw_proxy_destroy((struct pw_proxy*)registry);
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pw_core_disconnect(core);
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pw_context_destroy(context);
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pw_main_loop_destroy(loop);
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return 0;
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}
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```
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To compile the simple test application, copy it into a tutorial3.c file and
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use:
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```
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gcc -Wall tutorial3.c -o tutorial3 $(pkg-config --cflags --libs libpipewire-0.3)
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```
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[previous](tutorial2.md) [index](tutorial-index.md) [next](tutorial4.md)
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