examples: add another ringbuffer example

This one use a thread-loop and uses a blocking push into a ringbuffer.

src/examples/audio-src-ring2.c

@@ -0,0 +1,248 @@
+/* PipeWire */
+/* SPDX-FileCopyrightText: Copyright © 2024 Wim Taymans */
+/* SPDX-License-Identifier: MIT */
+
+/*
+ [title]
+ Audio source using \ref pw_stream "pw_stream" and ringbuffer.
+
+ This one uses a thread-loop and does a blocking push into a
+ ringbuffer.
+ [title]
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <math.h>
+#include <signal.h>
+
+#include <spa/param/audio/format-utils.h>
+#include <spa/utils/ringbuffer.h>
+
+#include <pipewire/pipewire.h>
+
+#define M_PI_M2f (float)(M_PI+M_PI)
+
+#define DEFAULT_RATE		44100
+#define DEFAULT_CHANNELS	2
+#define DEFAULT_VOLUME		0.7f
+
+#define BUFFER_SIZE		(16*1024)
+
+struct data {
+	struct pw_thread_loop *thread_loop;
+	struct pw_loop *loop;
+	struct pw_stream *stream;
+	int eventfd;
+	bool running;
+
+	float accumulator;
+
+	struct spa_ringbuffer ring;
+	float buffer[BUFFER_SIZE * DEFAULT_CHANNELS];
+};
+
+static void fill_f32(struct data *d, uint32_t offset, int n_frames)
+{
+	float val;
+	int i, c;
+
+        for (i = 0; i < n_frames; i++) {
+                d->accumulator += M_PI_M2f * 440 / DEFAULT_RATE;
+                if (d->accumulator >= M_PI_M2f)
+                        d->accumulator -= M_PI_M2f;
+
+                val = sinf(d->accumulator) * DEFAULT_VOLUME;
+                for (c = 0; c < DEFAULT_CHANNELS; c++)
+                        d->buffer[((offset + i) % BUFFER_SIZE) * DEFAULT_CHANNELS + c] = val;
+        }
+}
+
+/* this is called from the main-thread as fast as possible. It will block until
+ * more data can be written */
+static void push_refill(void *userdata)
+{
+	struct data *data = userdata;
+	int32_t filled;
+	uint32_t index, avail;
+	uint64_t count;
+
+	while (true) {
+		filled = spa_ringbuffer_get_write_index(&data->ring, &index);
+		/* we xrun, this can not happen because we never read more
+		 * than what there is in the ringbuffer and we never write more than
+		 * what is left */
+		spa_assert(filled >= 0);
+		spa_assert(filled <= BUFFER_SIZE);
+
+		/* this is how much samples we can write */
+		avail = BUFFER_SIZE - filled;
+		if (avail > 0)
+			break;
+
+		/* no space.. block and wait for free space */
+		spa_system_eventfd_read(data->loop->system, data->eventfd, &count);
+	}
+	/* write new samples to the ringbuffer from the given index */
+	fill_f32(data, index, avail);
+
+	/* and advance the ringbuffer */
+	spa_ringbuffer_write_update(&data->ring, index + avail);
+}
+
+/* our data processing function is in general:
+ *
+ *  struct pw_buffer *b;
+ *  b = pw_stream_dequeue_buffer(stream);
+ *
+ *  .. generate stuff in the buffer ...
+ *  In this case we read samples from a ringbuffer. The ringbuffer is
+ *  filled up by another thread.
+ *
+ *  pw_stream_queue_buffer(stream, b);
+ */
+static void on_process(void *userdata)
+{
+	struct data *data = userdata;
+	struct pw_buffer *b;
+	struct spa_buffer *buf;
+	uint8_t *p;
+	uint32_t index, to_read, to_silence;
+	int32_t avail, n_frames, stride;
+
+	if ((b = pw_stream_dequeue_buffer(data->stream)) == NULL) {
+		pw_log_warn("out of buffers: %m");
+		return;
+	}
+
+	buf = b->buffer;
+	if ((p = buf->datas[0].data) == NULL)
+		return;
+
+	/* the amount of space in the ringbuffer and the read index */
+	avail = spa_ringbuffer_get_read_index(&data->ring, &index);
+
+	stride = sizeof(float) * DEFAULT_CHANNELS;
+	n_frames = buf->datas[0].maxsize / stride;
+	if (b->requested)
+		n_frames = SPA_MIN((int32_t)b->requested, n_frames);
+
+	/* we can read if there is something available */
+	to_read = avail > 0 ? SPA_MIN(avail, n_frames) : 0;
+	/* and fill the remainder with silence */
+	to_silence = n_frames - to_read;
+
+	if (to_read > 0) {
+		/* read data into the buffer */
+		spa_ringbuffer_read_data(&data->ring,
+				data->buffer, BUFFER_SIZE * stride,
+				(index % BUFFER_SIZE) * stride,
+				p, to_read * stride);
+		/* update the read pointer */
+		spa_ringbuffer_read_update(&data->ring, index + to_read);
+	}
+	if (to_silence > 0)
+		/* set the rest of the buffer to silence */
+		memset(SPA_PTROFF(p, to_read * stride, void), 0, to_silence * stride);
+
+	buf->datas[0].chunk->offset = 0;
+	buf->datas[0].chunk->stride = stride;
+	buf->datas[0].chunk->size = n_frames * stride;
+
+	pw_stream_queue_buffer(data->stream, b);
+
+	/* signal the main thread to fill the ringbuffer, we can only do this, for
+	 * example when the available ringbuffer space falls below a certain
+	 * level. */
+	spa_system_eventfd_write(data->loop->system, data->eventfd, 1);
+}
+
+static const struct pw_stream_events stream_events = {
+	PW_VERSION_STREAM_EVENTS,
+	.process = on_process,
+};
+
+static void do_quit(void *userdata, int signal_number)
+{
+	struct data *data = userdata;
+	data->running = false;
+}
+
+int main(int argc, char *argv[])
+{
+	struct data data = { 0, };
+	const struct spa_pod *params[1];
+	uint8_t buffer[1024];
+	struct pw_properties *props;
+	struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buffer, sizeof(buffer));
+
+	pw_init(&argc, &argv);
+
+	data.thread_loop = pw_thread_loop_new("audio-src", NULL);
+	data.loop = pw_thread_loop_get_loop(data.thread_loop);
+	data.running = true;
+
+	pw_thread_loop_lock(data.thread_loop);
+	pw_loop_add_signal(data.loop, SIGINT, do_quit, &data);
+	pw_loop_add_signal(data.loop, SIGTERM, do_quit, &data);
+
+	spa_ringbuffer_init(&data.ring);
+	if ((data.eventfd = spa_system_eventfd_create(data.loop->system, SPA_FD_CLOEXEC)) < 0)
+                return data.eventfd;
+
+	pw_thread_loop_start(data.thread_loop);
+
+	props = pw_properties_new(PW_KEY_MEDIA_TYPE, "Audio",
+			PW_KEY_MEDIA_CATEGORY, "Playback",
+			PW_KEY_MEDIA_ROLE, "Music",
+			NULL);
+	if (argc > 1)
+		/* Set stream target if given on command line */
+		pw_properties_set(props, PW_KEY_TARGET_OBJECT, argv[1]);
+
+	data.stream = pw_stream_new_simple(
+			data.loop,
+			"audio-src-ring",
+			props,
+			&stream_events,
+			&data);
+
+	/* Make one parameter with the supported formats. The SPA_PARAM_EnumFormat
+	 * id means that this is a format enumeration (of 1 value). */
+	params[0] = spa_format_audio_raw_build(&b, SPA_PARAM_EnumFormat,
+			&SPA_AUDIO_INFO_RAW_INIT(
+				.format = SPA_AUDIO_FORMAT_F32,
+				.channels = DEFAULT_CHANNELS,
+				.rate = DEFAULT_RATE ));
+
+	/* Now connect this stream. We ask that our process function is
+	 * called in a realtime thread. */
+	pw_stream_connect(data.stream,
+			  PW_DIRECTION_OUTPUT,
+			  PW_ID_ANY,
+			  PW_STREAM_FLAG_AUTOCONNECT |
+			  PW_STREAM_FLAG_MAP_BUFFERS |
+			  PW_STREAM_FLAG_RT_PROCESS,
+			  params, 1);
+
+	/* prefill the ringbuffer */
+	push_refill(&data);
+
+	pw_thread_loop_start(data.thread_loop);
+	pw_thread_loop_unlock(data.thread_loop);
+
+	while (data.running) {
+		/* just keep on pushing data as fast as we can, this can be done
+		 * from any thread. */
+		push_refill(&data);
+	}
+
+	pw_thread_loop_lock(data.thread_loop);
+	pw_stream_destroy(data.stream);
+	pw_thread_loop_unlock(data.thread_loop);
+	pw_thread_loop_destroy(data.thread_loop);
+	close(data.eventfd);
+	pw_deinit();
+
+	return 0;
+}

src/examples/meson.build

@@ -2,6 +2,7 @@
 examples = [
   'audio-src',
   'audio-src-ring',
+  'audio-src-ring2',
   'audio-dsp-src',
   'audio-dsp-filter',
   'audio-capture',