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PiperOrigin-RevId: 253489161
2019-06-16 16:06:57 -07:00
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+// Copyright 2019 The MediaPipe Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef MEDIAPIPE_FRAMEWORK_TOOL_SIMULATION_CLOCK_H_
+#define MEDIAPIPE_FRAMEWORK_TOOL_SIMULATION_CLOCK_H_
+
+#include <map>
+#include <set>
+
+#include "absl/base/thread_annotations.h"
+#include "absl/synchronization/mutex.h"
+#include "absl/time/time.h"
+#include "mediapipe/framework/deps/clock.h"
+
+namespace mediapipe {
+
+// A Clock that simulates the passage of time as quickly as possible.
+// Parallel threads can call Sleep() and be woken in the proper order.
+// Simulated time can be advanced by calling SleepUntil for the desired
+// clock time.  Clock time does not advance until all woken threads have
+// finished or gone back to sleep.
+//
+// In case multiple threads are scheduled to wake at the same time, they
+// wake in the order in which they called Sleep().  No thread is permitted
+// to continue until all earlier threads have finished or entered Sleep.
+// The result is a single well-defined order of events.  Any desired
+// order of events can be defined by adjusting the precise sleep times.
+class SimulationClock : public mediapipe::Clock {
+ public:
+  SimulationClock() {}
+  ~SimulationClock() override {}
+
+  // Returns the simulated time.
+  absl::Time TimeNow() override;
+
+  // Sleeps until the specified duration has elapsed according to this clock.
+  void Sleep(absl::Duration d) override;
+
+  // Sleeps until the specifed wakeup_time.
+  void SleepUntil(absl::Time wakeup_time) override;
+
+  // Informs this clock that a woken thread has started running.
+  void ThreadStart();
+
+  // Informs this clock that a woken thread has finished running.
+  void ThreadFinish();
+
+ protected:
+  // Queue up wake up waiter.
+  void SleepInternal(absl::Time wakeup_time)
+      EXCLUSIVE_LOCKS_REQUIRED(time_mutex_);
+  // Advances to the next wake up time if no related threads are running.
+  void TryAdvanceTime() EXCLUSIVE_LOCKS_REQUIRED(time_mutex_);
+
+  // Represents a thread blocked in SleepUntil.
+  struct Waiter {
+    bool sleeping = true;
+    absl::CondVar cond;
+  };
+
+ protected:
+  absl::Mutex time_mutex_;
+  absl::Time time_ GUARDED_BY(time_mutex_);
+  std::multimap<absl::Time, Waiter*> waiters_ GUARDED_BY(time_mutex_);
+  int num_running_ GUARDED_BY(time_mutex_) = 0;
+};
+
+}  // namespace mediapipe
+
+#endif  // MEDIAPIPE_FRAMEWORK_TOOL_SIMULATION_CLOCK_H_