mpd/src/event_pipe.c

/* the Music Player Daemon (MPD)
 * Copyright (C) 2003-2007 Warren Dukes <warren.dukes@gmail.com>
 * Copyright (C) 2008 Eric Wong <normalperson@yhbt.net>
 *
 * This project's homepage is: http://www.musicpd.org
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include "event_pipe.h"
#include "utils.h"
#include "log.h"

#include <assert.h>
#include <glib.h>
#include <string.h>

GThread *main_task;
static int event_pipe[2];
static GMutex *event_pipe_mutex;
static bool pipe_events[PIPE_EVENT_MAX];
static event_pipe_callback_t event_pipe_callbacks[PIPE_EVENT_MAX];

/**
 * Invoke the callback for a certain event.
 */
static void
event_pipe_invoke(enum pipe_event event)
{
	assert((unsigned)event < PIPE_EVENT_MAX);
	assert(event != PIPE_EVENT_SIGNAL);
	assert(event_pipe_callbacks[event] != NULL);

	event_pipe_callbacks[event]();
}

static bool consume_pipe(void)
{
	char buffer[256];
	ssize_t r = read(event_pipe[0], buffer, sizeof(buffer));
	bool events[PIPE_EVENT_MAX];

	if (r < 0 && errno != EAGAIN && errno != EINTR)
		FATAL("error reading from pipe: %s\n", strerror(errno));

	g_mutex_lock(event_pipe_mutex);
	memcpy(events, pipe_events, sizeof(events));
	memset(pipe_events, 0, sizeof(pipe_events));
	g_mutex_unlock(event_pipe_mutex);

	for (unsigned i = 0; i < PIPE_EVENT_MAX; ++i)
		if (i != PIPE_EVENT_SIGNAL && events[i])
			/* invoke the event handler; the SIGNAL event
			   has no handler, because it is handled by
			   the event_pipe_wait() caller */
			event_pipe_invoke(i);

	return events[PIPE_EVENT_SIGNAL];
}

static gboolean
main_notify_event(G_GNUC_UNUSED GIOChannel *source,
		  G_GNUC_UNUSED GIOCondition condition,
		  G_GNUC_UNUSED gpointer data)
{
	consume_pipe();
	return true;
}

void event_pipe_init(void)
{
	GIOChannel *channel;

	main_task = g_thread_self();

	if (pipe(event_pipe) < 0)
		g_error("Couldn't open pipe: %s", strerror(errno));
	if (set_nonblocking(event_pipe[1]) < 0)
		g_error("Couldn't set non-blocking I/O: %s", strerror(errno));

	channel = g_io_channel_unix_new(event_pipe[0]);
	g_io_add_watch(channel, G_IO_IN, main_notify_event, NULL);
	g_io_channel_unref(channel);

	event_pipe_mutex = g_mutex_new();

	main_task = g_thread_self();
}

void event_pipe_deinit(void)
{
	g_mutex_free(event_pipe_mutex);

	xclose(event_pipe[0]);
	xclose(event_pipe[1]);
}

void
event_pipe_register(enum pipe_event event, event_pipe_callback_t callback)
{
	assert(event != PIPE_EVENT_SIGNAL);
	assert((unsigned)event < PIPE_EVENT_MAX);
	assert(event_pipe_callbacks[event] == NULL);

	event_pipe_callbacks[event] = callback;
}

void event_pipe_emit(enum pipe_event event)
{
	ssize_t w;

	assert((unsigned)event < PIPE_EVENT_MAX);

	g_mutex_lock(event_pipe_mutex);
	if (pipe_events[event]) {
		/* already set: don't write */
		g_mutex_unlock(event_pipe_mutex);
		return;
	}

	pipe_events[event] = true;
	g_mutex_unlock(event_pipe_mutex);

	w = write(event_pipe[1], "", 1);
	if (w < 0 && errno != EAGAIN && errno != EINTR)
		g_error("error writing to pipe: %s", strerror(errno));
}

void event_pipe_emit_fast(enum pipe_event event)
{
	assert((unsigned)event < PIPE_EVENT_MAX);

	pipe_events[event] = true;
	write(event_pipe[1], "", 1);
}

void event_pipe_signal(void)
{
	event_pipe_emit(PIPE_EVENT_SIGNAL);
}

void event_pipe_wait(void)
{
	consume_pipe();
}