fix some thread-safty issue and simplify threadpool

test=develop

Author: panyx0718

paddle/fluid/framework/threadpool.cc

@@ -34,6 +34,11 @@ ThreadPool* ThreadPool::GetInstance() {
   return threadpool_.get();
 }
 
+void ThreadPool::Reset() {
+  threadpool_.reset(nullptr);
+  ThreadPool::Init();
+}
+
 void ThreadPool::Init() {
   if (threadpool_.get() == nullptr) {
     // TODO(Yancey1989): specify the max threads number
@@ -59,6 +64,7 @@ ThreadPool::ThreadPool(int num_threads)
 ThreadPool::~ThreadPool() {
   {
     // notify all threads to stop running
+    std::lock_guard<std::mutex> l(mutex_);
     running_ = false;
     scheduled_.notify_all();
   }
@@ -69,19 +75,18 @@ ThreadPool::~ThreadPool() {
   }
 }
 
-void ThreadPool::Wait() {
-  std::unique_lock<std::mutex> lock(mutex_);
-  completed_.wait(lock, [=] { return Done() == true; });
-}
-
 void ThreadPool::TaskLoop() {
-  while (running_) {
+  while (true) {
     std::unique_lock<std::mutex> lock(mutex_);
-    scheduled_.wait(lock, [=] { return !tasks_.empty() || !running_; });
 
-    if (!running_) {
-      break;
+    scheduled_.wait(
+        lock, [this] { return !this->tasks_.empty() || !this->running_; });
+
+    std::lock_guard<std::mutex> l(mutex_);
+    if (!running_ || tasks_.empty()) {
+      return;
     }
+
     // pop a task from the task queue
     auto task = std::move(tasks_.front());
     tasks_.pop();
@@ -91,14 +96,6 @@ void ThreadPool::TaskLoop() {
 
     // run the task
     task();
-
-    {
-      std::unique_lock<std::mutex> lock(mutex_);
-      ++idle_threads_;
-      if (Done()) {
-        completed_.notify_all();
-      }
-    }
   }
 }
 

paddle/fluid/framework/threadpool.h

@@ -55,16 +55,10 @@ class ThreadPool {
   // Returns the singleton of ThreadPool.
   static ThreadPool* GetInstance();
 
-  ~ThreadPool();
-
-  // Returns the number of threads created by the constructor.
-  size_t Threads() const { return total_threads_; }
+  // delete current thread pool and create a new one.
+  static void Reset();
 
-  // Returns the number of currently idle threads.
-  size_t IdleThreads() {
-    std::unique_lock<std::mutex> lock(mutex_);
-    return idle_threads_;
-  }
+  ~ThreadPool();
 
   // Run pushes a function to the task queue and returns a std::future
   // object.  To wait for the completion of the task, call
@@ -94,25 +88,13 @@ class ThreadPool {
     });
     std::future<std::unique_ptr<platform::EnforceNotMet>> f = task.get_future();
     tasks_.push(std::move(task));
-    lock.unlock();
     scheduled_.notify_one();
     return f;
   }
 
-  // Wait until all the tasks are completed.
-  void Wait();
-
  private:
   DISABLE_COPY_AND_ASSIGN(ThreadPool);
 
-  // If the task queue is empty and avaialbe is equal to the number of
-  // threads, means that all tasks are completed.  Note: this function
-  // is not thread-safe.  Returns true if all tasks are completed.
-  // Note: don't delete the data member total_threads_ and use
-  // threads_.size() instead; because you'd need to lock the mutex
-  // before accessing threads_.
-  bool Done() { return tasks_.empty() && idle_threads_ == total_threads_; }
-
   // The constructor starts threads to run TaskLoop, which retrieves
   // and runs tasks from the queue.
   void TaskLoop();

paddle/fluid/framework/threadpool_test.cc

@@ -52,6 +52,6 @@ TEST(ThreadPool, ConcurrentRun) {
   for (auto& t : threads) {
     t.join();
   }
-  pool->Wait();
+  framework::ThreadPool::Reset();
   EXPECT_EQ(sum, ((n + 1) * n) / 2);
 }