Fix SRL hang when exit. (#291)

* Fix SRL hang when exit.

* Error occurred when enable Async Load in TestDataProvider.
  * It because DataProvider is calling getNextBatchInternal in one thread, and destructing DataProvider in other thread.
  * Add wait routine in DataProvider destructing.
* Also fix another bug, when destructing TestDataProvider and do not read any test data.

Fix #286

* Follow comments, Use mutex is cool!

demo/semantic_role_labeling/.gitignore

+*.pyc
+train.log
+data/feature
+data/conll05st-release/
+data/src.dict
+data/test.wsj.props
+data/test.wsj.seq_pair
+data/test.wsj.words
+data/tgt.dict
+output

paddle/gserver/dataproviders/DataProvider.cpp

@@ -131,9 +131,10 @@ void DoubleBuffer::asyncLoadBatch() {
     taskReadySem_.wait();
     if (stopping_) break;
 
-    while (batchSize_ == 0) {
+    while (batchSize_ == 0 && !stopping_) {
       usleep(5);
     }
+    if (stopping_) break;
 
     do {
       DataBatch newBatch;

paddle/gserver/dataproviders/PyDataProvider2.cpp

@@ -433,26 +433,34 @@ private:
 
   inline void resetImpl(bool startNewThread) {
     DBG << "Reseting " << startNewThread;
+    exit_.store(true);
     if (loadThread_) {  // is loading.
-      exit_.store(true);
       loadThread_->join();
       loadThread_.reset();
     }
     {
       PyGuard g;
       callingContexts_.clear();
+      this->pullCV_.notify_one();
+    }
+
+    std::lock_guard<std::mutex> guard(mutexForReset_);
+    {
+      PyGuard g;
       dataPool_.clear();
     }
     poolActualSize_ = 0;
-    exit_ = false;
+
     if (startNewThread && cache_->reset()) {
       DBG << "Start new thread.";
       loadThread_.reset(new std::thread([this] {
+        exit_ = false;
         loadThread();
       }));
       callingContextCreated_.wait();
     }
     DBG << "Reset done";
+    exit_ = false;
   }
 
 private:
@@ -465,6 +473,8 @@ private:
   std::condition_variable pullCV_;
   std::mutex mtx_;
 
+  std::mutex mutexForReset_;
+
   ThreadBarrier callingContextCreated_;
   std::unique_ptr<IPyDataProviderCache> cache_;
 
@@ -529,6 +539,7 @@ public:
    * Loading a batch of data.
    */
   int64_t getNextBatchInternal(int64_t size_, DataBatch *batch) {
+    std::lock_guard<std::mutex> guard(mutexForReset_);
     REGISTER_TIMER("PyDP2.getNextBatchInternal")
     CHECK_GE(size_, 0);
     size_t size = (size_t) size_;
@@ -554,6 +565,10 @@ public:
     } else {  // loading from cache.
       poolPtr = this->cache_->load();
     }
+    if (exit_) {
+      // PyDataProvider is destructing.
+      return 0;
+    }
     CHECK(poolPtr != nullptr);
 
     std::deque<PyObjectPtr>& pool = *poolPtr;

paddle/gserver/tests/test_PyDataProvider2.cpp

@@ -353,6 +353,23 @@ TEST(PyDataProvider2, test_check) {
   }
 }
 
+TEST(PyDataProvider2, multiThread) {
+  paddle::DataConfig config;
+  config.set_type("py2");
+  config.set_files(FLAGS_train_list.c_str());
+  config.set_load_data_module("test_PyDataProvider2");
+  config.set_load_data_object("test_dense_no_seq");
+  config.set_async_load_data(true);
+
+  std::unique_ptr<paddle::DataProvider> provider(
+      paddle::DataProvider::create(config, false));
+  provider->reset();
+  paddle::DataBatch batch;
+  provider->getNextBatch(100, &batch);
+  provider->reset();
+  provider.reset();
+}
+
 int main(int argc, char** argv) {
   testing::InitGoogleTest(&argc, argv);
   paddle::initMain(argc, argv);