Made it possible to customize the threadpool

unsupported/Eigen/CXX11/src/Tensor/TensorDeviceThreadPool.h

@@ -24,36 +24,40 @@ class ThreadPoolInterface {
 // The implementation of the ThreadPool type ensures that the Schedule method
 // runs the functions it is provided in FIFO order when the scheduling is done
 // by a single thread.
-class ThreadPool : public ThreadPoolInterface {
+// Environment provides a way to create threads and also allows to intercept
+// task submission and execution.
+template <typename Environment>
+class ThreadPoolTempl : public ThreadPoolInterface {
  public:
   // Construct a pool that contains "num_threads" threads.
-  explicit ThreadPool(int num_threads) : threads_(num_threads), waiters_(num_threads) {
+  explicit ThreadPoolTempl(int num_threads, Environment env = Environment())
+      : env_(env), threads_(num_threads), waiters_(num_threads) {
     for (int i = 0; i < num_threads; i++) {
-      threads_.push_back(new std::thread([this]() { WorkerLoop(); }));
+      threads_.push_back(env.CreateThread([this]() { WorkerLoop(); }));
     }
   }
 
   // Wait until all scheduled work has finished and then destroy the
   // set of threads.
-  ~ThreadPool()
-  {
+  ~ThreadPoolTempl() {
     {
       // Wait for all work to get done.
       std::unique_lock<std::mutex> l(mu_);
-      empty_.wait(l, [this]() { return pending_.empty(); });
+      while (!pending_.empty()) {
+        empty_.wait(l);
+      }
       exiting_ = true;
 
       // Wakeup all waiters.
       for (auto w : waiters_) {
         w->ready = true;
-        w->work = nullptr;
+        w->task.f = nullptr;
         w->cv.notify_one();
       }
     }
 
     // Wait for threads to finish.
     for (auto t : threads_) {
-      t->join();
       delete t;
     }
   }
@@ -61,14 +65,15 @@ class ThreadPool : public ThreadPoolInterface {
   // Schedule fn() for execution in the pool of threads. The functions are
   // executed in the order in which they are scheduled.
   void Schedule(std::function<void()> fn) {
+    Task t = env_.CreateTask(std::move(fn));
     std::unique_lock<std::mutex> l(mu_);
     if (waiters_.empty()) {
-      pending_.push_back(fn);
+      pending_.push_back(std::move(t));
     } else {
       Waiter* w = waiters_.back();
       waiters_.pop_back();
       w->ready = true;
-      w->work = fn;
+      w->task = std::move(t);
       w->cv.notify_one();
     }
   }
@@ -77,46 +82,76 @@ class ThreadPool : public ThreadPoolInterface {
   void WorkerLoop() {
     std::unique_lock<std::mutex> l(mu_);
     Waiter w;
+    Task t;
     while (!exiting_) {
-      std::function<void()> fn;
       if (pending_.empty()) {
         // Wait for work to be assigned to me
         w.ready = false;
         waiters_.push_back(&w);
-        w.cv.wait(l, [&w]() { return w.ready; });
-        fn = w.work;
-        w.work = nullptr;
+        while (!w.ready) {
+          w.cv.wait(l);
+        }
+        t = w.task;
+        w.task.f = nullptr;
       } else {
         // Pick up pending work
-        fn = pending_.front();
+        t = std::move(pending_.front());
         pending_.pop_front();
         if (pending_.empty()) {
           empty_.notify_all();
         }
       }
-      if (fn) {
+      if (t.f) {
         mu_.unlock();
-        fn();
+        env_.ExecuteTask(t);
+        t.f = nullptr;
         mu_.lock();
       }
     }
   }
 
  private:
+  typedef typename Environment::Task Task;
+  typedef typename Environment::EnvThread Thread;
+
   struct Waiter {
     std::condition_variable cv;
-    std::function<void()> work;
+    Task task;
     bool ready;
   };
 
+  Environment env_;
   std::mutex mu_;
-  MaxSizeVector<std::thread*> threads_;             // All threads
-  MaxSizeVector<Waiter*> waiters_;                  // Stack of waiting threads.
-  std::deque<std::function<void()>> pending_;       // Queue of pending work
-  std::condition_variable empty_;                   // Signaled on pending_.empty()
+  MaxSizeVector<Thread*> threads_;  // All threads
+  MaxSizeVector<Waiter*> waiters_;  // Stack of waiting threads.
+  std::deque<Task> pending_;          // Queue of pending work
+  std::condition_variable empty_;          // Signaled on pending_.empty()
   bool exiting_ = false;
 };
 
+struct StlThreadEnvironment {
+  struct Task {
+    std::function<void()> f;
+  };
+
+  // EnvThread constructor must start the thread,
+  // destructor must join the thread.
+  class EnvThread {
+   public:
+    EnvThread(std::function<void()> f) : thr_(f) {}
+    ~EnvThread() { thr_.join(); }
+
+   private:
+    std::thread thr_;
+  };
+
+  EnvThread* CreateThread(std::function<void()> f) { return new EnvThread(f); }
+  Task CreateTask(std::function<void()> f) { return Task{std::move(f)}; }
+  void ExecuteTask(const Task& t) { t.f(); }
+};
+
+typedef ThreadPoolTempl<StlThreadEnvironment> ThreadPool;
+
 
 // Barrier is an object that allows one or more threads to wait until
 // Notify has been called a specified number of times.