semproc++.cc

// g++ `pkg-config --cflags --libs glib-2.0` -pthread  semproc++.cc  -o semproc

/* Example to parallel progress a directed acyclic graph as described in
 * Chapter 17.3 of http://www.theses.fr/2017PA080116, page 131-135
 * https://gareus.org/misc/thesis-p8/2017-12-Gareus-Lat.pdf
 *
 * (C) 2017, 2019 Robin Gareus <[email protected]>
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */

/* Number of worker threads to start (in addition to main thread). Can be 0.
 * This should be user configurable and set to "available CPU cores - 1"
 */
#define N_WORKERS (3)

#include <cassert>
#include <cstdio>

#include <glib.h>
#include <pthread.h>
#include <semaphore.h>
#include <stdint.h>
#include <stdlib.h>
#include <time.h>

#include <list>
#include <set>
#include <string>
#include <vector>

/** Lock free multiple producer, multiple consumer queue
 *
 * inspired by http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue
 * Kudos to Dmitry Vyukov
 */
template <typename T>
class MPMCQueue
{
public:
	MPMCQueue (size_t buffer_size = 8)
		: _buffer (0)
		, _buffer_mask (0)
	{
		reserve (buffer_size);
	}

	~MPMCQueue ()
	{
		delete[] _buffer;
	}

	static size_t
	power_of_two_size (size_t sz)
	{
		int32_t power_of_two;
		for (power_of_two = 1; 1U << power_of_two < sz; ++power_of_two)
			;
		return 1U << power_of_two;
	}

	void
	reserve (size_t buffer_size)
	{
		buffer_size = power_of_two_size (buffer_size);
		assert ((buffer_size >= 2) && ((buffer_size & (buffer_size - 1)) == 0));
		if (_buffer_mask >= buffer_size - 1) {
			return;
		}
		delete[] _buffer;
		_buffer      = new cell_t[buffer_size];
		_buffer_mask = buffer_size - 1;
		clear ();
	}

	void
	clear ()
	{
		for (size_t i = 0; i <= _buffer_mask; ++i) {
			g_atomic_int_set (&_buffer[i]._sequence, i);
		}
		g_atomic_int_set (&_enqueue_pos, 0);
		g_atomic_int_set (&_dequeue_pos, 0);
	}

	bool
	push_back (T const& data)
	{
		cell_t* cell;
		guint   pos = g_atomic_int_get (&_enqueue_pos);
		for (;;) {
			cell         = &_buffer[pos & _buffer_mask];
			guint    seq = g_atomic_int_get (&cell->_sequence);
			intptr_t dif = (intptr_t)seq - (intptr_t)pos;
			if (dif == 0) {
				if (g_atomic_int_compare_and_exchange (&_enqueue_pos, pos, pos + 1)) {
					break;
				}
			} else if (dif < 0) {
				assert (0);
				return false;
			} else {
				pos = g_atomic_int_get (&_enqueue_pos);
			}
		}

		cell->_data = data;
		g_atomic_int_set (&cell->_sequence, pos + 1);
		return true;
	}

	bool
	dequeue (T& data)
	{
		cell_t* cell;
		guint   pos = g_atomic_int_get (&_dequeue_pos);
		for (;;) {
			cell         = &_buffer[pos & _buffer_mask];
			guint    seq = g_atomic_int_get (&cell->_sequence);
			intptr_t dif = (intptr_t)seq - (intptr_t) (pos + 1);
			if (dif == 0) {
				if (g_atomic_int_compare_and_exchange (&_dequeue_pos, pos, pos + 1)) {
					break;
				}
			} else if (dif < 0) {
				return false;
			} else {
				pos = g_atomic_int_get (&_dequeue_pos);
			}
		}

		data = cell->_data;
		g_atomic_int_set (&cell->_sequence, pos + _buffer_mask + 1);
		return true;
	}

private:
	struct cell_t {
		volatile guint _sequence;
		T              _data;
	};

	cell_t* _buffer;
	size_t  _buffer_mask;

	volatile guint _enqueue_pos;
	volatile guint _dequeue_pos;
};

class Graph;

/** A Process Graph Node to process */
class GraphNode {
public:
	GraphNode (Graph* g, std::string const& n)
		: _graph (g)
		, _name (n)
		, _refcount (0)
		, _init_refcount (0)
	{
		/* fake some work */
		_work_delay = 1 + rand () % 10;
	}

	void run ()
	{
		process ();
		finish ();
	}

	const char* cname () const { return _name.c_str (); }

	/* setup methods, to add graph edges.
	 * Must be called during initialization only.
	 *
	 * Note that this example does not include toplogical sorting.
	 * It is left to the graph-setup to order the DAG.
	 */

	/** add outgoing graph edge */
	void add_feeds (GraphNode* g)
	{
		_childnodes.insert (g);
	}

	/** add incoming graph edge */
	void add_depends ()
	{
		++_init_refcount;
		_refcount = _init_refcount;
	}

private:
	/* custom data to process this node.
	 * Here a sleep/delay in msec.
	 */
	gulong _work_delay;

protected:
	virtual void process ();

private:
	void finish ();
	void trigger ();

	Graph*      _graph; ///< parent Graph
	std::string _name;  ///< node name

	/** outgoing edges
	 * downstream nodes to activate when this node has completed processed */
	std::set<GraphNode*> _childnodes;

	/* upstream nodes reference count */
	gint _refcount;      ///< count-down (unprocessed upstream)
	gint _init_refcount; ///< number of incoming edges
};

/** Graph -- manage threads, schedule work and synchronize entry/exit */
class Graph {
public:
	Graph (unsigned int n_worker_threads)
		: _n_workers (n_worker_threads)
		, _n_terminal_nodes (0)
		, _setup_n_terminal_nodes (0)
	{
		sem_init (&_callback_start, 0, 0);
		sem_init (&_callback_done, 0, 0);
		sem_init (&_trigger, 0, 0);
		g_atomic_int_set (&_terminal_refcnt, 0);
		g_atomic_int_set (&_terminate, 0);
		g_atomic_int_set (&_idle_thread_cnt, 0);
		g_atomic_int_set (&_trigger_queue_size, 0);
	}

	~Graph ()
	{
		sem_destroy (&_callback_start);
		sem_destroy (&_callback_done);
		sem_destroy (&_trigger);
	}

	void process_graph ();

	bool start ();
	void terminate ();

	/* setup, create and connect nodes */
	GraphNode*
	add_node (std::string const& name)
	{
		_setup_graph_nodes.push_back (GraphNode (this, name));
		return &_setup_graph_nodes.back ();
	}

	GraphNode*
	add_terminal_node (std::string const& name)
	{
		++_setup_n_terminal_nodes;
		return add_node (name);
	}

	GraphNode*
	add_initial_node (std::string const& name)
	{
		GraphNode* n = add_node (name);
		_setup_init_trigger_list.push_back (n);
		return n;
	}

	void clear_setup ()
	{
		_setup_graph_nodes.clear ();
		_setup_init_trigger_list.clear ();
		_setup_n_terminal_nodes = 0;
	}

	void rechain ()
	{
		assert (g_atomic_int_get (&_terminal_refcnt) == 0);
		assert (g_atomic_int_get (&_trigger_queue_size) == 0);

		_graph_nodes.swap (_setup_graph_nodes);
		_init_trigger_list.swap (_setup_init_trigger_list);

		_n_terminal_nodes = _setup_n_terminal_nodes;
		g_atomic_int_set (&_terminal_refcnt, _n_terminal_nodes);

		_trigger_queue.reserve (_graph_nodes.size ());

		clear_setup ();
	}

	static void
	connect (GraphNode* from, GraphNode* to)
	{
		from->add_feeds (to);
		to->add_depends ();
	}


private:
	friend class GraphNode;

	void trigger (GraphNode* n);
	void reached_terminal_node ();

private:
	static void*
	start_main_thread (void* g)
	{
		static_cast<Graph*> (g)->main_thread ();
		return NULL;
	}

	static void*
	start_worker (void* g)
	{
		static_cast<Graph*> (g)->worker_thread ();
		return NULL;
	}

	void worker_thread ();
	void main_thread ();

	pthread_t _main_thread;
	std::vector<pthread_t> _worker_threads;

	/* number of work-threads to start/started.
	 * After ::start() this is equivalent to
	 * _worker_threads.size ()
	 */
	int _n_workers;

	/* flag to terminate background threads */
	volatile gint _terminate;

	/** List of all graph nodes (only used for memory management) */
	std::list<GraphNode> _graph_nodes;

	/** Nodes without incoming edges.
	 * These run concurrently at the start of each cycle to kick off processing */
	std::list<GraphNode*> _init_trigger_list;

	/** Synchronize with entry point */
	sem_t _callback_start;
	sem_t _callback_done;

	/** Start worker threads */
	sem_t _trigger;

	/* Terminal node reference count */
	volatile gint _terminal_refcnt;  ///< remaining unprocessed terminal nodes in this cycle
	size_t        _n_terminal_nodes; ///< number of graph nodes without an outgoing edge

	MPMCQueue<GraphNode*> _trigger_queue;      ///< nodes that can be processed
	volatile guint        _trigger_queue_size; ///< number of entries in trigger-queue
	volatile guint        _idle_thread_cnt;    ///< number of threads waiting for work

	/* Chain used to setup in the background.
	 * This is applied and cleared by ::rechain()
	 */
	std::list<GraphNode>  _setup_graph_nodes;
	std::list<GraphNode*> _setup_init_trigger_list;
	size_t                _setup_n_terminal_nodes;

};

/* **************************
 * GraphNode Implementation */

/* Process a node */
void
GraphNode::process ()
{
	/* XXX the actual work is to be performed here XXX */
	printf ("Thread 0x%zx: process '%s' (%lums)\n", pthread_self (), cname (), _work_delay);
	g_usleep (1000 * _work_delay);
}

/* Called by an upstream node, when it has completed processing */
void
GraphNode::trigger ()
{
	/* check if we can run */
	if (g_atomic_int_dec_and_test (&_refcount)) {
		/* reset reference count for next cycle */
		g_atomic_int_set (&_refcount, _init_refcount);
		/* all nodes that feed this node have completed, so this node be processed now. */
		_graph->trigger (this);
	}
}

/* Completed processing this node, notify outgoing edges */
void
GraphNode::finish ()
{
	bool feeds = false;
	/* notify downstream nodes that depend on this node */
	for (auto i : _childnodes) {
		// printf ("%s activates %s\n", cname(), i->cname());
		i->trigger ();
		feeds = true;
	}
	if (!feeds) {
		/* terminal node, notify graph */
		_graph->reached_terminal_node ();
	}
}

/* **********************
 * Graph Implementation *
 * *********************/

void
Graph::main_thread ()
{
	/* Wait until all worker threads are active */
	while (g_atomic_int_get (&_idle_thread_cnt) != _n_workers) {
		sched_yield ();
	}

	/* Wait for initial process callback */
	sem_wait (&_callback_start);

	/* first time setup */

	/* Can't run without a graph */
	assert (_graph_nodes.size () > 0);
	assert (_init_trigger_list.size () > 0);
	assert (_n_terminal_nodes > 0);

	/* Bootstrap the trigger-list
	 * (later this is done by Graph_reached_terminal_node) */
	for (auto i : _init_trigger_list) {
		g_atomic_int_inc (&_trigger_queue_size);
		_trigger_queue.push_back (i);
	}

	/* After setup, the main-thread just becomes a normal worker */
	worker_thread ();
}

void
Graph::worker_thread ()
{
	for (;;) {
		GraphNode* to_run = NULL;

		if (g_atomic_int_get (&_terminate)) {
			return;
		}

		if (_trigger_queue.dequeue (to_run)) {
			/* Wake up idle threads, but at most as many as there's
			 * work in the trigger queue that can be processed by
			 * other threads.
			 * This thread as not yet decreased _trigger_queue_size.
			 */
			guint idle_cnt   = g_atomic_int_get (&_idle_thread_cnt);
			guint work_avail = g_atomic_int_get (&_trigger_queue_size);
			guint wakeup     = std::min (idle_cnt + 1, work_avail);

			for (guint i = 1; i < wakeup; ++i) {
				sem_post (&_trigger);
			}
		}

		while (!to_run) {
			/* Wait for work, fall asleep */
			g_atomic_int_inc (&_idle_thread_cnt);
			assert (g_atomic_int_get (&_idle_thread_cnt) <= _n_workers);

			sem_wait (&_trigger);

			if (g_atomic_int_get (&_terminate)) {
				return;
			}

			g_atomic_int_dec_and_test (&_idle_thread_cnt);

			/* Try to find some work to do */
			_trigger_queue.dequeue (to_run);
		}

		/* Process the graph-node */
		g_atomic_int_dec_and_test (&_trigger_queue_size);
		to_run->run ();
	}
}

/* Called from a node when all its incoming edges have
 * completed processing and the node can run.
 * It is added to the "work queue" */
void
Graph::trigger (GraphNode* n)
{
	g_atomic_int_inc (&_trigger_queue_size);
	_trigger_queue.push_back (n);
}

/* Called from a terminal node (from the Graph worked-thread)
 * to indicate it has completed processing.
 *
 * The thread of the last terminal node that reaches here
 * will inform the main-thread, wait, and kick off the next process cycle.
 */
void
Graph::reached_terminal_node ()
{
	if (g_atomic_int_dec_and_test (&_terminal_refcnt)) {
		/* All terminal nodes have completed.
		 * We're done with this cycle.
		 */
		assert (g_atomic_int_get (&_trigger_queue_size) == 0);

		/* Notify caller */
		sem_post (&_callback_done);

		/* Ensure that all background threads are idle.
		 * When freewheeling there may be an immediate restart:
		 * If there are more threads than CPU cores, some worker-
		 * threads may only be "on the way" to become idle.
		 */
		while (g_atomic_int_get (&_idle_thread_cnt) != _n_workers) {
			sched_yield ();
		}

		/* Now wait for the next cycle to begin */
		sem_wait (&_callback_start);

		if (g_atomic_int_get (&_terminate)) {
			return;
		}

		/* Reset terminal reference count */
		g_atomic_int_set (&_terminal_refcnt, _n_terminal_nodes);

		/* and start the initial nodes */
		for (auto i : _init_trigger_list) {
			g_atomic_int_inc (&_trigger_queue_size);
			_trigger_queue.push_back (i);
		}
		/* .. continue in worker-thread */
	}
}

bool
Graph::start ()
{
	/* XXX These really should be realtime threads for audio processing XXX
	 *
	 * eg. jack_client_create_thread() or setting up priority using
	 * pthread_attr_setschedpolicy()  pthread_attr_setschedparam()
	 * and/or mach  thread_policy_set()
	 *
	 * alternatively expose Graph::start_worker(),
	 * Graph::start_main_thread() to the DAW's backend/engine.
	 */

	/* Start worker threads */
	for (int i = 0; i < _n_workers; ++i) {
		pthread_t tid;
		if (0 == pthread_create (&tid, NULL, Graph::start_worker, this)) {
			_worker_threads.push_back (tid);
		}
	}

	_n_workers = _worker_threads.size ();

	/* .. and the main thread */
	if (pthread_create (&_main_thread, NULL, Graph::start_main_thread, this)) {
		terminate ();
		return false;
	}

	/* Breathe */
	sched_yield ();
	return true;
}

/* Tell all threads to terminate */
void
Graph::terminate ()
{
	/* Flag threads to terminate */
	g_atomic_int_set (&_terminate, 1);

	/* Wake-up sleeping threads */
	int tc = g_atomic_int_get (&_idle_thread_cnt);
	assert (tc == _n_workers);
	for (int i = 0; i < tc; ++i) {
		sem_post (&_trigger);
	}
	/* and the main thread */
	sem_post (&_callback_start);

	/* join threads */
	for (auto i : _worker_threads) {
		pthread_join (i, NULL);
	}
	pthread_join (_main_thread, NULL);

}

/* The actual entry-point to start processing all nodes,
 * and wait for them to complete */
void
Graph::process_graph ()
{
	printf (" -- START PROCESS --\n");
	const int64_t start = g_get_monotonic_time ();
	sem_post (&_callback_start);
	sem_wait (&_callback_done);
	const int64_t end = g_get_monotonic_time ();
	printf (" -- END PROCESS - ELAPSED: %.1fms\n", (end - start) / 1e3f);
}

/* ****************************************************************************/

static void
setup_graph (Graph& g)
{
	/* Setup an ordered process graph.
	 *
	 * https://en.wikipedia.org/wiki/Directed_acyclic_graph
	 * https://en.wikipedia.org/wiki/Topological_sorting
	 */

	/* The GraphNode constructor also need to be changed to have
	 * a pointer to the node-processing method.
	 * In this example GraphNode::process() just sleeps to simulate work.
	 *
	 * An alternative approach is to subclass
	 *    class YourProcessNode : public GraphNode;
	 * and overload  GraphNode::process();
	 */

#if 0
	/* Create some example graph
	 *
	 *       [master]
	 *        ^    ^
	 *    [bus-1] [bus-2]
	 *    ^   ^     ^
	 *  [T1] [T2]  [T3]
	 *
	 * https://gareus.org/misc/thesis-p8/2017-12-Gareus-Lat.pdf
	 * Fig. 31, Table 7; page 134, 135
	 */
	GraphNode* master = g.add_terminal_node ("master");
	GraphNode* bus2   = g.add_node ("bus2");
	GraphNode* bus1   = g.add_node ("bus1");
	GraphNode* track3 = g.add_initial_node ("track3");
	GraphNode* track2 = g.add_initial_node ("track2");
	GraphNode* track1 = g.add_initial_node ("track1");

	g.connect (bus1, master);
	g.connect (bus2, master);

	g.connect (track1, bus1);
	g.connect (track2, bus2);
	g.connect (track3, bus2);
#else
	/* some more complex graph
	 *         [out-1]           [out-2]
	 *        /   |   \         /       \
	 *  [L1-1] [L1-2] [L1-3] [L1-4]  [L1-5]
	 *   /   \   |   \  |   /    \   /
	 * [L2-1] [L2-2] [L2-3 ]     [L2-4]
	 *   |       |  \   |        /   \
	 * [L3-1] [L3-2] [L3-3]  [L3-4] [L3-5]
	 *   |   /             \    |  /
	 * [L4-1]               `[L4-2]
	 *
	 */
	GraphNode* out1 = g.add_terminal_node ("out-1");
	GraphNode* out2 = g.add_terminal_node ("out-2");

	GraphNode* l1_1 = g.add_node ("L1-1");
	GraphNode* l1_2 = g.add_node ("L1-2");
	GraphNode* l1_3 = g.add_node ("L1-3");
	GraphNode* l1_4 = g.add_node ("L1-4");
	GraphNode* l1_5 = g.add_node ("L1-5");

	GraphNode* l2_1 = g.add_node ("L2-1");
	GraphNode* l2_2 = g.add_node ("L2-2");
	GraphNode* l2_3 = g.add_node ("L2-3");
	GraphNode* l2_4 = g.add_node ("L2-4");

	GraphNode* l3_1 = g.add_node ("L3-1");
	GraphNode* l3_2 = g.add_node ("L3-2");
	GraphNode* l3_3 = g.add_node ("L3-3");
	GraphNode* l3_4 = g.add_node ("L3-4");
	GraphNode* l3_5 = g.add_node ("L3-5");

	GraphNode* l4_1 = g.add_initial_node ("L4-1");
	GraphNode* l4_2 = g.add_initial_node ("L4-2");

	g.connect (l1_1, out1);
	g.connect (l1_2, out1);
	g.connect (l1_3, out1);
	g.connect (l1_4, out2);
	g.connect (l1_5, out2);

	g.connect (l2_1, l1_1);
	g.connect (l2_2, l1_2);

	g.connect (l2_3, l1_2);
	g.connect (l2_3, l1_3);
	g.connect (l2_3, l1_4);

	g.connect (l2_4, l1_4);
	g.connect (l2_4, l1_5);

	g.connect (l3_1, l2_1);
	g.connect (l3_2, l2_2);
	g.connect (l3_3, l2_2);
	g.connect (l3_4, l2_4);
	g.connect (l3_5, l2_4);
	g.connect (l3_3, l2_3);

	g.connect (l4_1, l3_1);
	g.connect (l4_1, l3_2);
	g.connect (l4_2, l3_3);
	g.connect (l4_2, l3_4);
	g.connect (l4_2, l3_5);
#endif

	/* The graph has a dedicated setup chain.
	 * When the process-graph changes, a second graph is build in the background,
	 * while the current graph continues processing.
	 *
	 * rechain() activates the setup graph and drops the previous graph.
	 * It must not be called concurrently with processing.
	 *
	 * ie. it can only be called before or after ::process_graph().
	 */
	g.rechain ();
}

int
main (int argc, char** argv)
{
	srand (time (NULL));

	Graph g (N_WORKERS);

	/* start process threads */
	g.start ();

	/* Add some nodes to process */
	setup_graph (g);

	/* Process a few times */
	for (int i = 0; i < 5; ++i) {
		g.process_graph ();
	}

	/* Cleanup and quit */
	g.terminate ();

	return 0;
}