WorkerPool.hpp

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#pragma once
 
#include <atomic>
#include <condition_variable>
#include <cstddef>
#include <functional>
#include <mutex>
#include <thread>
#include <vector>
 
class WorkerPool
{
public:
    explicit WorkerPool(int numWorkers);
 
    ~WorkerPool();
 
    WorkerPool(const WorkerPool&) = delete;
    WorkerPool& operator=(const WorkerPool&) = delete;
    WorkerPool(WorkerPool&&) = delete;
    WorkerPool& operator=(WorkerPool&&) = delete;

    [[nodiscard]] int numWorkers() const noexcept { return static_cast<int>(workers_.size()); }

    void parallelFor(int count, const std::function<void(int begin, int end)>& fn);
 
private:
    void workerLoop(int workerId);
 
    std::vector<std::thread> workers_;
 
    // Job hand-off state.  The main thread sets `currentFn_` + `currentTotal_`
    // + `currentChunkSize_` + bumps `generation_`, then notifies all workers.
    // Each worker grabs its `workerId` chunk.  When all workers (and the
    // caller's inline chunk) finish, `outstanding_` reaches zero and the
    // caller is unblocked.
    std::mutex mtx_;
    std::condition_variable cvWork_;
    std::condition_variable cvDone_;
    const std::function<void(int, int)>* currentFn_ = nullptr;
    int currentTotal_ = 0;
    int currentChunkSize_ = 0;
    int currentGeneration_ = 0;
    std::atomic<int> outstanding_{0};
    std::atomic<bool> stop_{false};
};