Fix deadlock in parallel executor (#891)

Fix deadlock in parallel executor
  Execute immediately if ParalellFor has only 1 task

onnxruntime/core/common/threadpool.cc

@@ -4,6 +4,8 @@
 #include "core/platform/threadpool.h"
 #include "core/common/common.h"
 
+#include <cassert>
+
 #ifdef USE_EIGEN_THREADPOOL
 #if defined(_MSC_VER)
 #pragma warning(disable : 4267)
@@ -24,7 +26,6 @@
 namespace onnxruntime {
 
 namespace concurrency {
-#ifdef USE_EIGEN_THREADPOOL
 
 // TODO: This is temporarily taken from Eigen until we upgrade its version.
 // Barrier is an object that allows one or more threads to wait until
@@ -32,20 +33,20 @@ namespace concurrency {
 class Barrier {
  public:
   Barrier(unsigned int count) : state_(count << 1), notified_(false) {
-    eigen_assert(((count << 1) >> 1) == count);
+    assert(((count << 1) >> 1) == count);
   }
   ~Barrier() {
-    eigen_assert((state_ >> 1) == 0);
+    assert((state_ >> 1) == 0);
   }
 
   void Notify() {
     unsigned int v = state_.fetch_sub(2, std::memory_order_acq_rel) - 2;
     if (v != 1) {
-      eigen_assert(((v + 2) & ~1) != 0);
+      assert(((v + 2) & ~1) != 0);
       return;  // either count has not dropped to 0, or waiter is not waiting
     }
     std::unique_lock<std::mutex> l(mu_);
-    eigen_assert(!notified_);
+    assert(!notified_);
     notified_ = true;
     cv_.notify_all();
   }
@@ -66,6 +67,7 @@ class Barrier {
   bool notified_;
 };
 
+#ifdef USE_EIGEN_THREADPOOL
 class ThreadPool::Impl : public Eigen::ThreadPool {
  public:
   Impl(const std::string& name, int num_threads)
@@ -77,8 +79,7 @@ class ThreadPool::Impl : public Eigen::ThreadPool {
     // TODO: Eigen supports a more efficient ThreadPoolDevice mechanism
     // We will simply rely on the work queue and stealing in the short term.
     Barrier barrier(static_cast<unsigned int>(total));
-    std::function<void(int32_t)> handle_iteration;
-    handle_iteration = [=, &handle_iteration, &barrier, &fn](int iteration) {
+    std::function<void(int32_t)> handle_iteration = [&barrier, &fn](int iteration) {
       fn(iteration);
       barrier.Notify();
     };
@@ -94,8 +95,7 @@ class ThreadPool::Impl : public Eigen::ThreadPool {
     // TODO: Eigen supports a more efficient ThreadPoolDevice mechanism
     // We will simply rely on the work queue and stealing in the short term.
     Barrier barrier(static_cast<unsigned int>(last - first + 1));
-    std::function<void(int64_t, int64_t)> handle_range;
-    handle_range = [=, &handle_range, &barrier, &fn](int64_t first, int64_t last) {
+    std::function<void(int64_t, int64_t)> handle_range = [&barrier, &fn](int64_t first, int64_t last) {
       fn(first, last);
       barrier.Notify();
     };
@@ -127,11 +127,16 @@ class ThreadPool::Impl : public TaskThreadPool {
       fn(id);
     }
 #else
+    Barrier barrier(static_cast<unsigned int>(total));
+    std::function<void(int32_t)> handle_iteration = [&barrier, &fn](int iteration) {
+      fn(iteration);
+      barrier.Notify();
+    };
     for (int32_t id = 0; id < total; ++id) {
-      std::packaged_task<void()> task(std::bind(fn, id));
+      std::packaged_task<void()> task(std::bind(handle_iteration, id));
       RunTask(std::move(task));
     }
-    WaitWorkComplete();
+    barrier.Wait();
 #endif
   }
 
@@ -142,11 +147,16 @@ class ThreadPool::Impl : public TaskThreadPool {
       fn(id, id + 1);
     }
 #else
+    Barrier barrier(static_cast<unsigned int>(last - first + 1));
+    std::function<void(int64_t, int64_t)> handle_iteration = [&barrier, &fn](int64_t first, int64_t last) {
+      fn(first, last);
+      barrier.Notify();
+    };
     for (int64_t id = first; id < last; ++id) {
-      std::packaged_task<void()> task(std::bind(fn, id, id + 1));
+      std::packaged_task<void()> task(std::bind(handle_iteration, id, id + 1));
       RunTask(std::move(task));
     }
-    WaitWorkComplete();
+    barrier.Wait();
 #endif
   }
 };
@@ -162,7 +172,10 @@ ThreadPool::ThreadPool(const std::string& name, int num_threads)
 void ThreadPool::Schedule(std::function<void()> fn) { impl_->Schedule(fn); }
 
 void ThreadPool::ParallelFor(int32_t total, std::function<void(int32_t)> fn) {
-  if (total <= 0) {
+  if (total <= 0) return;
+
+  if (total == 1) {
+    fn(0);
     return;
   }
 
@@ -170,7 +183,8 @@ void ThreadPool::ParallelFor(int32_t total, std::function<void(int32_t)> fn) {
 }
 
 void ThreadPool::ParallelForRange(int64_t first, int64_t last, std::function<void(int64_t, int64_t)> fn) {
-  if (last <= first) {
+  if (last <= first) return;
+  if (last - first == 1) {
     fn(first, last);
     return;
   }