OpenSpace/modules/globebrowsing/other/lruthreadpool.h

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 *                                                                                       *
 * OpenSpace                                                                             *
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 * Copyright (c) 2014-2017                                                               *
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#ifndef __OPENSPACE_MODULE_GLOBEBROWSING___LRU_THREAD_POOL___H__
#define __OPENSPACE_MODULE_GLOBEBROWSING___LRU_THREAD_POOL___H__

#include <modules/globebrowsing/cache/lrucache.h>

#include <condition_variable>
#include <functional>
#include <mutex>
#include <queue>
#include <thread>
#include <vector>

// Implementatin based on http://progsch.net/wordpress/?p=81

namespace openspace {
namespace globebrowsing {    

template<typename KeyType>
class LRUThreadPool;

template<typename KeyType>
class LRUThreadPoolWorker {
public: 
    LRUThreadPoolWorker(LRUThreadPool<KeyType>& pool);
    void operator()();
private:
    LRUThreadPool<KeyType>& _pool;
};

/**
 * The <code>LRUThreadPool</code> will only enqueue a certain number of tasks. The most
 * recently enqueued task is the one that will be executed first. This class is templated
 * on a key type which used as an identifier to determine wheter or not a task with the
 * given key has been enqueued or not. This means that a task can be enqueued several
 * times. The user must ensure that an enqueued task with a given key should be
 * equal in outcome to a second enqueued task with the same key. This is because a second
 * enqueued task with the same key will simply be bumped and prioritised before other
 * enqueued tasks. The given task will be ignored.
 */
template<typename KeyType>
class LRUThreadPool {
public:
    LRUThreadPool(size_t numThreads, size_t queueSize);
    ~LRUThreadPool();

    void enqueue(std::function<void()> f, KeyType key);
    bool touch(KeyType key);
    std::vector<KeyType> getQueuedTasksKeys();
    std::vector<KeyType> getUnqueuedTasksKeys();
    void clearEnqueuedTasks();

private:
    
    struct DefaultHasher {
        unsigned long long operator()(const KeyType& key) const {
            return static_cast<unsigned long long>(key);
        }
    };
    friend class LRUThreadPoolWorker<KeyType>;

    std::vector<std::thread> _workers;
    cache::LRUCache<KeyType, std::function<void()>, DefaultHasher> _queuedTasks;
    std::vector<KeyType> _unqueuedTasks;
    std::mutex _queueMutex;
    std::condition_variable _condition;

    bool _stop;
};

} // namespace globebrowsing
} // namespace openspace

#include "lruthreadpool.inl"

#endif // __OPENSPACE_MODULE_GLOBEBROWSING___LRU_THREAD_POOL___H__