--- a
+++ b/src/workqueue.h
@@ -0,0 +1,361 @@
+/* Copyright (C) 2006-2016 J.F.Dockes
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; 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>
+#if HAVE_STD_FUTURE
+#include <future>
+#endif
+#include <string>
+#include <queue>
+#include <list>
+#include <mutex>
+#include <condition_variable>
+
+#ifdef MDU_INCLUDE_LOG
+#include MDU_INCLUDE_LOG
+#else
+#include "log.h"
+#endif
+
+/**
+ * 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.
+ *
+ * The strange thread functions argument and return values
+ * comes from compatibility with an earlier pthread-based
+ * implementation.
+ */
+template <class T> class WorkQueue {
+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 std::string& name, size_t hi = 0, size_t lo = 1)
+ : m_name(name), m_high(hi), m_low(lo), m_workers_exited(0),
+ m_ok(true), m_clients_waiting(0), m_workers_waiting(0),
+ m_tottasks(0), m_nowake(0), m_workersleeps(0), m_clientsleeps(0) {
+ }
+
+ ~WorkQueue() {
+ if (!m_worker_threads.empty()) {
+ 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(int nworkers, void *(workproc)(void *), void *arg) {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ for (int i = 0; i < nworkers; i++) {
+ Worker w;
+#if HAVE_STD_FUTURE
+ std::packaged_task<void *(void *)> task(workproc);
+ w.res = task.get_future();
+ w.thr = std::thread(std::move(task), arg);
+#else
+ w.thr = std::thread(workproc, arg);
+#endif
+ m_worker_threads.push_back(std::move(w));
+ }
+ return true;
+ }
+
+ /** Add item to work queue, called from client.
+ *
+ * Sleeps if there are already too many.
+ */
+ bool put(T t, bool flushprevious = false) {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ if (!ok()) {
+ LOGERR("WorkQueue::put:" << m_name << ": !ok\n");
+ return false;
+ }
+
+ while (ok() && m_high > 0 && m_queue.size() >= m_high) {
+ m_clientsleeps++;
+ // Keep the order: we test ok() AFTER the sleep...
+ m_clients_waiting++;
+ m_ccond.wait(lock);
+ if (!ok()) {
+ m_clients_waiting--;
+ return false;
+ }
+ m_clients_waiting--;
+ }
+ if (flushprevious) {
+ while (!m_queue.empty()) {
+ m_queue.pop();
+ }
+ }
+
+ m_queue.push(t);
+ if (m_workers_waiting > 0) {
+ // Just wake one worker, there is only one new task.
+ m_wcond.notify_one();
+ } else {
+ m_nowake++;
+ }
+
+ return true;
+ }
+
+ /** Wait until the queue is inactive. Called from client.
+ *
+ * Waits until the task queue is empty and the workers are all
+ * back sleeping. Used by the client to wait for all current work
+ * to be completed, when it needs to perform work that couldn't be
+ * done in parallel with the worker's tasks, or before shutting
+ * down. Work can be resumed after calling this. Note that the
+ * only thread which can call it safely is the client just above
+ * (which can control the task flow), else there could be
+ * tasks in the intermediate queues.
+ * To rephrase: there is no warranty on return that the queue is actually
+ * idle EXCEPT if the caller knows that no jobs are still being created.
+ * It would be possible to transform this into a safe call if some kind
+ * of suspend condition was set on the queue by waitIdle(), to be reset by
+ * some kind of "resume" call. Not currently the case.
+ */
+ bool waitIdle() {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ if (!ok()) {
+ LOGERR("WorkQueue::waitIdle:" << m_name << ": not ok\n");
+ return false;
+ }
+
+ // We're done when the queue is empty AND all workers are back
+ // waiting for a task.
+ while (ok() && (m_queue.size() > 0 ||
+ m_workers_waiting != m_worker_threads.size())) {
+ m_clients_waiting++;
+ m_ccond.wait(lock);
+ m_clients_waiting--;
+ }
+
+ return ok();
+ }
+
+ /** Tell the workers to exit, and wait for them.
+ *
+ * Does not bother about tasks possibly remaining on the queue, so
+ * should be called after waitIdle() for an orderly shutdown.
+ */
+ void *setTerminateAndWait() {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ LOGDEB("setTerminateAndWait:" << m_name << "\n");
+
+ if (m_worker_threads.empty()) {
+ // Already called ?
+ return (void*)0;
+ }
+
+ // Wait for all worker threads to have called workerExit()
+ m_ok = false;
+ while (m_workers_exited < m_worker_threads.size()) {
+ m_wcond.notify_all();
+ m_clients_waiting++;
+ m_ccond.wait(lock);
+ m_clients_waiting--;
+ }
+
+ LOGINFO("" << m_name << ": tasks " << m_tottasks << " nowakes " <<
+ m_nowake << " wsleeps " << m_workersleeps << " csleeps " <<
+ m_clientsleeps << "\n");
+ // Perform the thread joins and compute overall status
+ // Workers return (void*)1 if ok
+ void *statusall = (void*)1;
+ while (!m_worker_threads.empty()) {
+#if HAVE_STD_FUTURE
+ void *status = m_worker_threads.front().res.get();
+#else
+ void *status = (void*) 1;
+#endif
+ m_worker_threads.front().thr.join();
+ if (status == (void *)0) {
+ statusall = status;
+ }
+ m_worker_threads.pop_front();
+ }
+
+ // Reset to start state.
+ m_workers_exited = m_clients_waiting = m_workers_waiting =
+ m_tottasks = m_nowake = m_workersleeps = m_clientsleeps = 0;
+ m_ok = true;
+
+ LOGDEB("setTerminateAndWait:" << m_name << " done\n");
+ return statusall;
+ }
+
+ /** 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, size_t *szp = 0) {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ if (!ok()) {
+ LOGDEB("WorkQueue::take:" << m_name << ": not ok\n");
+ return false;
+ }
+
+ while (ok() && m_queue.size() < m_low) {
+ m_workersleeps++;
+ m_workers_waiting++;
+ if (m_queue.empty()) {
+ m_ccond.notify_all();
+ }
+ m_wcond.wait(lock);
+ if (!ok()) {
+ // !ok is a normal condition when shutting down
+ m_workers_waiting--;
+ return false;
+ }
+ m_workers_waiting--;
+ }
+
+ m_tottasks++;
+ *tp = m_queue.front();
+ if (szp) {
+ *szp = m_queue.size();
+ }
+ m_queue.pop();
+ if (m_clients_waiting > 0) {
+ // No reason to wake up more than one client thread
+ m_ccond.notify_one();
+ } else {
+ m_nowake++;
+ }
+ return true;
+ }
+
+ bool waitminsz(size_t sz) {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ if (!ok()) {
+ return false;
+ }
+
+ while (ok() && m_queue.size() < sz) {
+ m_workersleeps++;
+ m_workers_waiting++;
+ if (m_queue.empty()) {
+ m_ccond.notify_all();
+ }
+ m_wcond.wait(lock);
+ if (!ok()) {
+ m_workers_waiting--;
+ return false;
+ }
+ m_workers_waiting--;
+ }
+ 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 m_ok is set to
+ * false by the shutdown code anyway). The thread must return/exit
+ * immediately after calling this.
+ */
+ void workerExit() {
+ LOGDEB("workerExit:" << m_name << "\n");
+ std::unique_lock<std::mutex> lock(m_mutex);
+ m_workers_exited++;
+ m_ok = false;
+ m_ccond.notify_all();
+ }
+
+ size_t qsize() {
+ std::unique_lock<std::mutex> lock(m_mutex);
+ return m_queue.size();
+ }
+
+private:
+ bool ok() {
+ bool isok = m_ok && m_workers_exited == 0 && !m_worker_threads.empty();
+ if (!isok) {
+ LOGDEB("WorkQueue:ok:" << m_name << ": not ok m_ok " << m_ok <<
+ " m_workers_exited " << m_workers_exited <<
+ " m_worker_threads size " << m_worker_threads.size() <<
+ "\n");
+ }
+ return isok;
+ }
+
+ struct Worker {
+ std::thread thr;
+#if HAVE_STD_FUTURE
+ std::future<void *> res;
+#endif
+ };
+
+ // Configuration
+ std::string m_name;
+ size_t m_high;
+ size_t m_low;
+
+ // Worker threads having called exit. Used to decide when we're done
+ unsigned int m_workers_exited;
+ // Status
+ bool m_ok;
+
+ // Our threads.
+ std::list<Worker> m_worker_threads;
+
+ // Jobs input queue
+ std::queue<T> m_queue;
+
+ // Synchronization
+ std::condition_variable m_ccond;
+ std::condition_variable m_wcond;
+ std::mutex m_mutex;
+
+ // Client/Worker threads currently waiting for a job
+ unsigned int m_clients_waiting;
+ unsigned int m_workers_waiting;
+
+ // Statistics
+ unsigned int m_tottasks;
+ unsigned int m_nowake;
+ unsigned int m_workersleeps;
+ unsigned int m_clientsleeps;
+};
+
+#endif /* _WORKQUEUE_H_INCLUDED_ */
+