/* Copyright (C) 2012-2016 J.F.Dockes
* 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.
*/
#ifndef _WORKQUEUE_H_INCLUDED_
#define _WORKQUEUE_H_INCLUDED_
#include <thread>
#include <future>
#include <string>
#include <queue>
#include <list>
#include <mutex>
#include <condition_variable>
#include "log.h"
/**
* 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++) {
std::packaged_task<void *(void *)> task(workproc);
Worker w;
w.res = task.get_future();
w.thr = std::thread(std::move(task), arg);
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()) {
void *status = m_worker_threads.front().res.get();
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;
std::future<void *> res;
};
// 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_ */