gst: Add a pool and an allocator implementation

This is needed to track the lifetime of the FrameBufferAllocator in relation to
the GstBuffer/GstMemory objects travelling inside GStreamer.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/gstreamer/gstlibcamerapool.cpp

@@ -0,0 +1,110 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2020, Collabora Ltd.
+ *     Author: Nicolas Dufresne <nicolas.dufresne@collabora.com>
+ *
+ * gstlibcamerapool.cpp - GStreamer Buffer Pool
+ */
+
+#include "gstlibcamerapool.h"
+
+#include <libcamera/stream.h>
+
+#include "gstlibcamera-utils.h"
+
+using namespace libcamera;
+
+struct _GstLibcameraPool {
+	GstBufferPool parent;
+
+	GstAtomicQueue *queue;
+	GstLibcameraAllocator *allocator;
+	Stream *stream;
+};
+
+G_DEFINE_TYPE(GstLibcameraPool, gst_libcamera_pool, GST_TYPE_BUFFER_POOL);
+
+static GstFlowReturn
+gst_libcamera_pool_acquire_buffer(GstBufferPool *pool, GstBuffer **buffer,
+				  GstBufferPoolAcquireParams *params)
+{
+	GstLibcameraPool *self = GST_LIBCAMERA_POOL(pool);
+	GstBuffer *buf = GST_BUFFER(gst_atomic_queue_pop(self->queue));
+	if (!buf)
+		return GST_FLOW_ERROR;
+
+	if (!gst_libcamera_allocator_prepare_buffer(self->allocator, self->stream, buf))
+		return GST_FLOW_ERROR;
+
+	*buffer = buf;
+	return GST_FLOW_OK;
+}
+
+static void
+gst_libcamera_pool_reset_buffer(GstBufferPool *pool, GstBuffer *buffer)
+{
+	GstBufferPoolClass *klass = GST_BUFFER_POOL_CLASS(gst_libcamera_pool_parent_class);
+
+	/* Clears all the memories and only pool the GstBuffer objects */
+	gst_buffer_remove_all_memory(buffer);
+	klass->reset_buffer(pool, buffer);
+	GST_BUFFER_FLAGS(buffer) = 0;
+}
+
+static void
+gst_libcamera_pool_release_buffer(GstBufferPool *pool, GstBuffer *buffer)
+{
+	GstLibcameraPool *self = GST_LIBCAMERA_POOL(pool);
+	gst_atomic_queue_push(self->queue, buffer);
+}
+
+static void
+gst_libcamera_pool_init(GstLibcameraPool *self)
+{
+	self->queue = gst_atomic_queue_new(4);
+}
+
+static void
+gst_libcamera_pool_finalize(GObject *object)
+{
+	GstLibcameraPool *self = GST_LIBCAMERA_POOL(object);
+	GstBuffer *buf;
+
+	while ((buf = GST_BUFFER(gst_atomic_queue_pop(self->queue))))
+		gst_buffer_unref(buf);
+
+	gst_atomic_queue_unref(self->queue);
+	g_object_unref(self->allocator);
+
+	G_OBJECT_CLASS(gst_libcamera_pool_parent_class)->finalize(object);
+}
+
+static void
+gst_libcamera_pool_class_init(GstLibcameraPoolClass *klass)
+{
+	auto *object_class = G_OBJECT_CLASS(klass);
+	auto *pool_class = GST_BUFFER_POOL_CLASS(klass);
+
+	object_class->finalize = gst_libcamera_pool_finalize;
+	pool_class->start = nullptr;
+	pool_class->acquire_buffer = gst_libcamera_pool_acquire_buffer;
+	pool_class->reset_buffer = gst_libcamera_pool_reset_buffer;
+	pool_class->release_buffer = gst_libcamera_pool_release_buffer;
+}
+
+GstLibcameraPool *
+gst_libcamera_pool_new(GstLibcameraAllocator *allocator, Stream *stream)
+{
+	auto *pool = GST_LIBCAMERA_POOL(g_object_new(GST_TYPE_LIBCAMERA_POOL, nullptr));
+
+	pool->allocator = GST_LIBCAMERA_ALLOCATOR(g_object_ref(allocator));
+	pool->stream = stream;
+
+	gsize pool_size = gst_libcamera_allocator_get_pool_size(allocator, stream);
+	for (gsize i = 0; i < pool_size; i++) {
+		GstBuffer *buffer = gst_buffer_new();
+		gst_atomic_queue_push(pool->queue, buffer);
+	}
+
+	return pool;
+}