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| -rw-r--r-- | src/lib/upnp/WorkQueue.hxx | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/src/lib/upnp/WorkQueue.hxx b/src/lib/upnp/WorkQueue.hxx new file mode 100644 index 000000000..fe8ce53f9 --- /dev/null +++ b/src/lib/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_ */ |