1 files changed, 206 insertions, 0 deletions
diff --git a/src/db/upnp/WorkQueue.hxx b/src/db/upnp/WorkQueue.hxx
new file mode 100644
index 000000000..fe8ce53f9
--- /dev/null
+++ b/src/db/upnp/WorkQueue.hxx
@@ -0,0 +1,206 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * 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.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef _WORKQUEUE_H_INCLUDED_
+#define _WORKQUEUE_H_INCLUDED_
+
+#include "thread/Mutex.hxx"
+#include "thread/Cond.hxx"
+
+#include <assert.h>
+#include <pthread.h>
+
+#include <string>
+#include <queue>
+
+#define LOGINFO(X)
+#define LOGERR(X)
+
+/**
+ * A WorkQueue manages the synchronisation around a queue of work items,
+ * where a number of client threads queue tasks and a number of worker
+ * threads take and execute them. The goal is to introduce some level
+ * of parallelism between the successive steps of a previously single
+ * threaded pipeline. For example data extraction / data preparation / index
+ * update, but this could have other uses.
+ *
+ * There is no individual task status return. In case of fatal error,
+ * the client or worker sets an end condition on the queue. A second
+ * queue could conceivably be used for returning individual task
+ * status.
+ */
+template <class T>
+class WorkQueue {
+	// Configuration
+	const std::string name;
+
+	// Status
+	// Worker threads having called exit
+	unsigned n_workers_exited;
+	bool ok;
+
+	unsigned n_threads;
+	pthread_t *threads;
+
+	// Synchronization
+	std::queue<T> queue;
+	Cond client_cond;
+	Cond worker_cond;
+	Mutex mutex;
+
+public:
+	/** Create a WorkQueue
+	 * @param name for message printing
+	 * @param hi number of tasks on queue before clients blocks. Default 0
+	 *    meaning no limit. hi == -1 means that the queue is disabled.
+	 * @param lo minimum count of tasks before worker starts. Default 1.
+	 */
+	WorkQueue(const char *_name)
+		:name(_name),
+		 n_workers_exited(0),
+		 ok(false),
+		 n_threads(0), threads(nullptr)
+	{
+	}
+
+	~WorkQueue() {
+		setTerminateAndWait();
+	}
+
+	/** Start the worker threads.
+	 *
+	 * @param nworkers number of threads copies to start.
+	 * @param start_routine thread function. It should loop
+	 *      taking (QueueWorker::take()) and executing tasks.
+	 * @param arg initial parameter to thread function.
+	 * @return true if ok.
+	 */
+	bool start(unsigned nworkers, void *(*workproc)(void *), void *arg)
+	{
+		const ScopeLock protect(mutex);
+
+		assert(nworkers > 0);
+		assert(!ok);
+		assert(n_threads == 0);
+		assert(threads == nullptr);
+
+		n_threads = nworkers;
+		threads = new pthread_t[n_threads];
+
+		for  (unsigned i = 0; i < nworkers; i++) {
+			int err;
+			if ((err = pthread_create(&threads[i], 0, workproc, arg))) {
+				LOGERR(("WorkQueue:%s: pthread_create failed, err %d\n",
+					name.c_str(), err));
+				return false;
+			}
+		}
+
+		ok = true;
+		return true;
+	}
+
+	/** Add item to work queue, called from client.
+	 *
+	 * Sleeps if there are already too many.
+	 */
+	template<typename U>
+	bool put(U &&u)
+	{
+		const ScopeLock protect(mutex);
+
+		queue.emplace(std::forward<U>(u));
+
+		// Just wake one worker, there is only one new task.
+		worker_cond.signal();
+
+		return true;
+	}
+
+
+	/** Tell the workers to exit, and wait for them.
+	 */
+	void setTerminateAndWait()
+	{
+		const ScopeLock protect(mutex);
+
+		// Wait for all worker threads to have called workerExit()
+		ok = false;
+		while (n_workers_exited < n_threads) {
+			worker_cond.broadcast();
+			client_cond.wait(mutex);
+		}
+
+		// Perform the thread joins and compute overall status
+		// Workers return (void*)1 if ok
+		for (unsigned i = 0; i < n_threads; ++i) {
+			void *status;
+			pthread_join(threads[i], &status);
+		}
+
+		delete[] threads;
+		threads = nullptr;
+		n_threads = 0;
+
+		// Reset to start state.
+		n_workers_exited = 0;
+	}
+
+	/** Take task from queue. Called from worker.
+	 *
+	 * Sleeps if there are not enough. Signal if we go to sleep on empty
+	 * queue: client may be waiting for our going idle.
+	 */
+	bool take(T &tp)
+	{
+		const ScopeLock protect(mutex);
+
+		if (!ok)
+			return false;
+
+		while (queue.empty()) {
+			worker_cond.wait(mutex);
+			if (!ok)
+				return false;
+		}
+
+		tp = std::move(queue.front());
+		queue.pop();
+		return true;
+	}
+
+	/** Advertise exit and abort queue. Called from worker
+	 *
+	 * This would happen after an unrecoverable error, or when
+	 * the queue is terminated by the client. Workers never exit normally,
+	 * except when the queue is shut down (at which point ok is set to
+	 * false by the shutdown code anyway). The thread must return/exit
+	 * immediately after calling this.
+	 */
+	void workerExit()
+	{
+		const ScopeLock protect(mutex);
+
+		n_workers_exited++;
+		ok = false;
+		client_cond.broadcast();
+	}
+};
+
+#endif /* _WORKQUEUE_H_INCLUDED_ */