v1.4.4

source/core/StarWorkerPool.hpp

@@ -0,0 +1,222 @@
+#ifndef STAR_WORKER_POOL_HPP
+#define STAR_WORKER_POOL_HPP
+
+#include "StarThread.hpp"
+
+namespace Star {
+
+STAR_EXCEPTION(WorkerPoolException, StarException);
+
+STAR_CLASS(WorkerPool);
+
+// Shareable handle for a WorkerPool computation that does not produce any
+// value.
+class WorkerPoolHandle {
+public:
+  // Returns true if the work is completed (either due to error or actual
+  // completion, will not re-throw)
+  bool done() const;
+
+  // Waits up to given millis for the computation to finish.  Returns true if
+  // the computation finished within the allotted time, false otherwise.  If
+  // the computation is finished but it threw an exception, it will be
+  // re-thrown here.
+  bool wait(unsigned millis) const;
+
+  // synonym for wait(0)
+  bool poll() const;
+
+  // Wait until the computation finishes completely.  If the computation threw
+  // an exception it will be re-thrown by this method.
+  void finish() const;
+
+private:
+  friend WorkerPool;
+
+  struct Impl {
+    Impl();
+
+    Mutex mutex;
+    ConditionVariable condition;
+    atomic<bool> done;
+    std::exception_ptr exception;
+  };
+
+  WorkerPoolHandle(shared_ptr<Impl> impl);
+
+  shared_ptr<Impl> m_impl;
+};
+
+// Shareable handle for a WorkerPool computation that produces a value.
+template <typename ResultType>
+class WorkerPoolPromise {
+public:
+  // Returns true if the work is completed (either due to error or actual
+  // completion, will not re-throw)
+  bool done() const;
+
+  // Waits for the given amount of time for the work to be completed.  If the
+  // work is completed, returns true.  If the producer function throws for any
+  // reason, this method will re-throw the exception.  If millis is zero, does
+  // not wait at all simply polls to see if the computation is finished.
+  bool wait(unsigned millis) const;
+
+  // synonym for wait(0)
+  bool poll() const;
+
+  // Blocks until the work is done, and returns the result.  May be called
+  // multiple times to access the result.  If the computation threw
+  // an exception it will be re-thrown by this method.
+  ResultType& get();
+  ResultType const& get() const;
+
+private:
+  friend WorkerPool;
+
+  struct Impl {
+    Mutex mutex;
+    ConditionVariable condition;
+    Maybe<ResultType> result;
+    std::exception_ptr exception;
+  };
+
+  WorkerPoolPromise(shared_ptr<Impl> impl);
+
+  shared_ptr<Impl> m_impl;
+};
+
+class WorkerPool {
+public:
+  // Creates a stopped pool
+  WorkerPool(String name);
+  // Creates a started pool
+  WorkerPool(String name, unsigned threadCount);
+  ~WorkerPool();
+
+  WorkerPool(WorkerPool&&);
+  WorkerPool& operator=(WorkerPool&&);
+
+  // Start the thread pool with the given thread count range, or if it is
+  // already started, reconfigure the thread counts.
+  void start(unsigned threadCount);
+
+  // Stop the thread pool, not necessarily finishing any pending jobs (may
+  // leave pending jobs on the queue).
+  void stop();
+
+  // Try to finish any remaining jobs, then stop the thread pool.  This method
+  // must not be called if the worker pool will continuously receive new work,
+  // as it may not ever complete if that is the case.  The work queue must
+  // eventually become empty for this to properly return.
+  void finish();
+
+  // Add the given work to the pool and return a handle for the work.  It not
+  // required that the caller of this method hold on to the worker handle, the
+  // work will be managed and completed regardless of the WorkerPoolHandle
+  // lifetime.
+  WorkerPoolHandle addWork(function<void()> work);
+
+  // Like addWork, but the worker is expected to produce some result.  The
+  // returned promise can be used to get this return value once the producer is
+  // complete.
+  template <typename ResultType>
+  WorkerPoolPromise<ResultType> addProducer(function<ResultType()> producer);
+
+private:
+  class WorkerThread : public Thread {
+  public:
+    // Starts automatically
+    WorkerThread(WorkerPool* parent);
+    ~WorkerThread();
+
+    void run() override;
+
+    WorkerPool* parent;
+    atomic<bool> shouldStop;
+    atomic<bool> waiting;
+  };
+
+  void queueWork(function<void()> work);
+
+  String m_name;
+  Mutex m_threadMutex;
+  List<unique_ptr<WorkerThread>> m_workerThreads;
+
+  Mutex m_workMutex;
+  ConditionVariable m_workCondition;
+  Deque<function<void()>> m_pendingWork;
+};
+
+template <typename ResultType>
+bool WorkerPoolPromise<ResultType>::done() const {
+  MutexLocker locker(m_impl->mutex);
+  return m_impl->result || m_impl->exception;
+}
+
+template <typename ResultType>
+bool WorkerPoolPromise<ResultType>::wait(unsigned millis) const {
+  MutexLocker locker(m_impl->mutex);
+
+  if (!m_impl->result && !m_impl->exception && millis != 0)
+    m_impl->condition.wait(m_impl->mutex, millis);
+
+  if (m_impl->exception)
+    std::rethrow_exception(m_impl->exception);
+
+  if (m_impl->result)
+    return true;
+
+  return false;
+}
+
+template <typename ResultType>
+bool WorkerPoolPromise<ResultType>::poll() const {
+  return wait(0);
+}
+
+template <typename ResultType>
+ResultType& WorkerPoolPromise<ResultType>::get() {
+  MutexLocker locker(m_impl->mutex);
+
+  if (!m_impl->result && !m_impl->exception)
+    m_impl->condition.wait(m_impl->mutex);
+
+  if (m_impl->exception)
+    std::rethrow_exception(m_impl->exception);
+
+  return *m_impl->result;
+}
+
+template <typename ResultType>
+ResultType const& WorkerPoolPromise<ResultType>::get() const {
+  return const_cast<WorkerPoolPromise*>(this)->get();
+}
+
+template <typename ResultType>
+WorkerPoolPromise<ResultType>::WorkerPoolPromise(shared_ptr<Impl> impl)
+  : m_impl(move(impl)) {}
+
+template <typename ResultType>
+WorkerPoolPromise<ResultType> WorkerPool::addProducer(function<ResultType()> producer) {
+  // Construct a worker pool promise and wrap the producer to signal the
+  // promise when finished.
+  auto workerPoolPromiseImpl = make_shared<typename WorkerPoolPromise<ResultType>::Impl>();
+  queueWork([workerPoolPromiseImpl, producer]() {
+    try {
+      auto result = producer();
+      MutexLocker promiseLocker(workerPoolPromiseImpl->mutex);
+      workerPoolPromiseImpl->result = move(result);
+      workerPoolPromiseImpl->condition.broadcast();
+    } catch (...) {
+      MutexLocker promiseLocker(workerPoolPromiseImpl->mutex);
+      workerPoolPromiseImpl->exception = std::current_exception();
+      workerPoolPromiseImpl->condition.broadcast();
+    }
+  });
+
+  return workerPoolPromiseImpl;
+}
+
+}
+
+#endif