libweston: Introduce zwp_linux_explicit_synchronization_v1

Introduce support for the zwp_linux_explicit_synchronization_unstable_v1
protocol with an implementation of the zwp_linux_explicit_synchronization_v1
interface.

Explicit synchronization provides a more versatile notification
mechanism for buffer readiness and availability, and can be used to
improve efficiency by integrating with related functionality in display
and graphics APIs.

In addition, the per-commit nature of the release events provided by
this protocol potentially offers a solution to a deficiency of the
wl_buffer.release event (see
https://gitlab.freedesktop.org/wayland/wayland/issues/46).

Support for this protocol depends on the capabilities of the backend, so
we don't register it by default but provide a function which each
backend will need to call. In this commit only the headless backend when
using the noop renderer supports this to enable testing.

Note that the zwp_surface_synchronization_v1 interface, which contains
the core functionality of the protocol, is not implemented in this
commit. Support for it will be added in future commits.

Changes in v7:
  - Added some information in the commit message about the benefits of
    the explicit sync protocol.

Changes in v6:
  - Fall back to advertising minor version 1 of the explicit sync protocol,
    although we support minor version 2 features, until the new
    wayland-protocols version is released.

Changes in v5:
  - Meson support.
  - Advertise minor version 2 of the explicit sync protocol.

Changes in v4:
  - Enable explicit sync support in the headless backend for all
    renderers.

Changes in v3:
  - Use wl_resource_get_version() instead of hardcoding version 1.
  - Use updated protocol interface names.
  - Use correct format specifier for resource id.
  - Change test name to 'linux-explicit-synchronization.weston'
    (s/_/-/g).

Changes in v2:
  - Move implementation to separate file so protocol can be registered
    on demand by backends.
  - Register protocol in headless+noop backend for testing purposes.

Signed-off-by: Alexandros Frantzis <alexandros.frantzis@collabora.com>

tests/linux-explicit-synchronization-test.c

@@ -0,0 +1,96 @@
+/*
+ * Copyright © 2018 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the
+ * next paragraph) shall be included in all copies or substantial
+ * portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "config.h"
+
+#include <string.h>
+
+#include "linux-explicit-synchronization-unstable-v1-client-protocol.h"
+#include "weston-test-client-helper.h"
+#include "wayland-server-protocol.h"
+
+static struct zwp_linux_explicit_synchronization_v1 *
+get_linux_explicit_synchronization(struct client *client)
+{
+	struct global *g;
+	struct global *global_sync = NULL;
+	struct zwp_linux_explicit_synchronization_v1 *sync = NULL;
+
+	wl_list_for_each(g, &client->global_list, link) {
+		if (strcmp(g->interface,
+			   zwp_linux_explicit_synchronization_v1_interface.name))
+			continue;
+
+		if (global_sync)
+			assert(!"Multiple linux explicit sync objects");
+
+		global_sync = g;
+	}
+
+	assert(global_sync);
+	assert(global_sync->version == 1);
+
+	sync = wl_registry_bind(
+			client->wl_registry, global_sync->name,
+			&zwp_linux_explicit_synchronization_v1_interface, 1);
+	assert(sync);
+
+	return sync;
+}
+
+static struct client *
+create_test_client(void)
+{
+	struct client *cl = create_client_and_test_surface(0, 0, 100, 100);
+	assert(cl);
+	return cl;
+}
+
+TEST(second_surface_synchronization_on_surface_raises_error)
+{
+	struct client *client = create_test_client();
+	struct zwp_linux_explicit_synchronization_v1 *sync =
+		get_linux_explicit_synchronization(client);
+	struct zwp_linux_surface_synchronization_v1 *surface_sync1;
+	struct zwp_linux_surface_synchronization_v1 *surface_sync2;
+
+	surface_sync1 =
+		zwp_linux_explicit_synchronization_v1_get_synchronization(
+			sync, client->surface->wl_surface);
+	client_roundtrip(client);
+
+	/* Second surface_synchronization creation should fail */
+	surface_sync2 =
+		zwp_linux_explicit_synchronization_v1_get_synchronization(
+			sync, client->surface->wl_surface);
+	expect_protocol_error(
+		client,
+		&zwp_linux_explicit_synchronization_v1_interface,
+		ZWP_LINUX_EXPLICIT_SYNCHRONIZATION_V1_ERROR_SYNCHRONIZATION_EXISTS);
+
+	zwp_linux_surface_synchronization_v1_destroy(surface_sync2);
+	zwp_linux_surface_synchronization_v1_destroy(surface_sync1);
+	zwp_linux_explicit_synchronization_v1_destroy(sync);
+}

tests/meson.build

@@ -127,6 +127,13 @@ tests_weston = [
 			input_timestamps_unstable_v1_protocol_c,
 		]
 	],
+	[
+		'linux-explicit-synchronization',
+		[
+			linux_explicit_synchronization_unstable_v1_client_protocol_h,
+			linux_explicit_synchronization_unstable_v1_protocol_c,
+		]
+	],
 	['internal-screenshot'],
 	[
 		'presentation',