ThreadPool::Run interface return std::future (#7099)

* Run interface return future

* delete unused comments

paddle/framework/threadpool.h

@@ -16,6 +16,7 @@ limitations under the License. */
 
 #include <condition_variable>
 #include <functional>
+#include <future>
 #include <mutex>
 #include <queue>
 #include <thread>
@@ -25,10 +26,11 @@ limitations under the License. */
 namespace paddle {
 namespace framework {
 
-typedef std::function<void()> Task;
-
 class ThreadPool {
  public:
+  typedef std::packaged_task<void()> Task;
+  typedef std::function<void()> Fun;
+
   /**
    * @brief   Get a instance of threadpool, the thread number will
    *          be specified as the number of hardware thread contexts
@@ -61,13 +63,18 @@ class ThreadPool {
   /**
    * @brief   Push a function to the queue, and will be scheduled and
    *          executed if a thread is available.
-   * @param[in] Task  will be pushed to the task queue.
+   * @param[in] Task, will be pushed to the task queue.
+   * @return    std::future<void>, we could wait for the task finished by
+   *            f.wait().
    */
-  void Run(const Task& fn) {
+  std::future<void> Run(const Fun& fn) {
     std::unique_lock<std::mutex> lock(mutex_);
-    tasks_.push(fn);
+    Task task(std::bind(fn));
+    std::future<void> f = task.get_future();
+    tasks_.push(std::move(task));
     lock.unlock();
     scheduled_.notify_one();
+    return f;
   }
 
   /**
@@ -110,7 +117,7 @@ class ThreadPool {
         break;
       }
       // pop a task from the task queue
-      auto task = tasks_.front();
+      auto task = std::move(tasks_.front());
       tasks_.pop();
 
       --available_;

paddle/framework/threadpool_test.cc

@@ -20,16 +20,21 @@ limitations under the License. */
 namespace framework = paddle::framework;
 
 void do_sum(framework::ThreadPool* pool, std::atomic<int>& sum, int cnt) {
+  std::vector<std::future<void>> fs;
   for (int i = 0; i < cnt; ++i) {
-    pool->Run([&sum]() { sum.fetch_add(1); });
+    auto f = pool->Run([&sum]() { sum.fetch_add(1); });
+    fs.push_back(std::move(f));
+  }
+  for (auto& f : fs) {
+    f.wait();
   }
 }
 
 TEST(ThreadPool, ConcurrentInit) {
   framework::ThreadPool* pool;
-  int concurrent_cnt = 50;
+  int n = 50;
   std::vector<std::thread> threads;
-  for (int i = 0; i < concurrent_cnt; ++i) {
+  for (int i = 0; i < n; ++i) {
     std::thread t([&pool]() { pool = framework::ThreadPool::GetInstance(); });
     threads.push_back(std::move(t));
   }
@@ -38,13 +43,13 @@ TEST(ThreadPool, ConcurrentInit) {
   }
 }
 
-TEST(ThreadPool, ConcurrentStart) {
+TEST(ThreadPool, ConcurrentRun) {
   framework::ThreadPool* pool = framework::ThreadPool::GetInstance();
   std::atomic<int> sum(0);
   std::vector<std::thread> threads;
-  int concurrent_cnt = 50;
+  int n = 50;
   // sum = (n * (n + 1)) / 2
-  for (int i = 1; i <= concurrent_cnt; ++i) {
+  for (int i = 1; i <= n; ++i) {
     std::thread t(do_sum, pool, std::ref(sum), i);
     threads.push_back(std::move(t));
   }
@@ -52,5 +57,5 @@ TEST(ThreadPool, ConcurrentStart) {
     t.join();
   }
   pool->Wait();
-  EXPECT_EQ(sum, ((concurrent_cnt + 1) * concurrent_cnt) / 2);
+  EXPECT_EQ(sum, ((n + 1) * n) / 2);
 }