Foxy: backport mutex_two_priorities #1516

rclcpp/CMakeLists.txt

@@ -39,6 +39,7 @@ set(${PROJECT_NAME}_SRCS
   src/rclcpp/clock.cpp
   src/rclcpp/context.cpp
   src/rclcpp/contexts/default_context.cpp
+  src/rclcpp/detail/mutex_two_priorities.cpp
   src/rclcpp/detail/rmw_implementation_specific_payload.cpp
   src/rclcpp/detail/rmw_implementation_specific_publisher_payload.cpp
   src/rclcpp/detail/rmw_implementation_specific_subscription_payload.cpp

rclcpp/include/rclcpp/detail/mutex_two_priorities.hpp

@@ -0,0 +1,76 @@
+// Copyright 2021 Open Source Robotics Foundation, Inc.
+//
+// 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 RCLCPP__DETAIL__MUTEX_TWO_PRIORITIES_HPP_
+#define RCLCPP__DETAIL__MUTEX_TWO_PRIORITIES_HPP_
+
+#include <condition_variable>
+#include <mutex>
+
+namespace rclcpp
+{
+namespace detail
+{
+/// \internal A mutex that has two locking mechanism, one with higher priority than the other.
+/**
+ * After the current mutex owner release the lock, a thread that used the high
+ * priority mechanism will have priority over threads that used the low priority mechanism.
+ */
+class MutexTwoPriorities
+{
+public:
+  class HighPriorityLockable
+  {
+public:
+    explicit HighPriorityLockable(MutexTwoPriorities & parent);
+
+    void lock();
+
+    void unlock();
+
+private:
+    MutexTwoPriorities & parent_;
+  };
+
+  class LowPriorityLockable
+  {
+public:
+    explicit LowPriorityLockable(MutexTwoPriorities & parent);
+
+    void lock();
+
+    void unlock();
+
+private:
+    MutexTwoPriorities & parent_;
+  };
+
+  HighPriorityLockable
+  get_high_priority_lockable();
+
+  LowPriorityLockable
+  get_low_priority_lockable();
+
+private:
+  std::condition_variable hp_cv_;
+  std::condition_variable lp_cv_;
+  std::mutex cv_mutex_;
+  size_t hp_waiting_count_{0u};
+  bool data_taken_{false};
+};
+
+}  // namespace detail
+}  // namespace rclcpp
+
+#endif  // RCLCPP__DETAIL__MUTEX_TWO_PRIORITIES_HPP_

rclcpp/include/rclcpp/executors/multi_threaded_executor.hpp

@@ -22,6 +22,7 @@
 #include <thread>
 #include <unordered_map>
 
+#include "rclcpp/detail/mutex_two_priorities.hpp"
 #include "rclcpp/executor.hpp"
 #include "rclcpp/macros.hpp"
 #include "rclcpp/memory_strategies.hpp"
@@ -81,12 +82,17 @@ class MultiThreadedExecutor : public rclcpp::Executor
 private:
   RCLCPP_DISABLE_COPY(MultiThreadedExecutor)
 
-  std::mutex wait_mutex_;
+  std::mutex wait_mutex_;  // Unused. Leave it for ABI compatibility.
   size_t number_of_threads_;
   bool yield_before_execute_;
   std::chrono::nanoseconds next_exec_timeout_;
 
   std::set<TimerBase::SharedPtr> scheduled_timers_;
+  static std::unordered_map<MultiThreadedExecutor *,
+    std::shared_ptr<detail::MutexTwoPriorities>> wait_mutex_set_;
+  static std::mutex shared_wait_mutex_;
+  // These variables are declared as static variables for ABI-compatibiliity.
+  // And they mimic member variables needed to backport from master.
 };
 
 }  // namespace executors

rclcpp/src/rclcpp/detail/mutex_two_priorities.cpp

@@ -0,0 +1,104 @@
+// Copyright 2021 Open Source Robotics Foundation, Inc.
+//
+// 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.
+
+#include "rclcpp/detail/mutex_two_priorities.hpp"
+
+#include <mutex>
+
+namespace rclcpp
+{
+namespace detail
+{
+
+using LowPriorityLockable = MutexTwoPriorities::LowPriorityLockable;
+using HighPriorityLockable = MutexTwoPriorities::HighPriorityLockable;
+
+HighPriorityLockable::HighPriorityLockable(MutexTwoPriorities & parent)
+: parent_(parent)
+{}
+
+void
+HighPriorityLockable::lock()
+{
+  std::unique_lock<std::mutex> guard{parent_.cv_mutex_};
+  if (parent_.data_taken_) {
+    ++parent_.hp_waiting_count_;
+    while (parent_.data_taken_) {
+      parent_.hp_cv_.wait(guard);
+    }
+    --parent_.hp_waiting_count_;
+  }
+  parent_.data_taken_ = true;
+}
+
+void
+HighPriorityLockable::unlock()
+{
+  bool notify_lp{false};
+  {
+    std::lock_guard<std::mutex> guard{parent_.cv_mutex_};
+    parent_.data_taken_ = false;
+    notify_lp = 0u == parent_.hp_waiting_count_;
+  }
+  if (notify_lp) {
+    parent_.lp_cv_.notify_one();
+  } else {
+    parent_.hp_cv_.notify_one();
+  }
+}
+
+LowPriorityLockable::LowPriorityLockable(MutexTwoPriorities & parent)
+: parent_(parent)
+{}
+
+void
+LowPriorityLockable::lock()
+{
+  std::unique_lock<std::mutex> guard{parent_.cv_mutex_};
+  while (parent_.data_taken_ || parent_.hp_waiting_count_) {
+    parent_.lp_cv_.wait(guard);
+  }
+  parent_.data_taken_ = true;
+}
+
+void
+LowPriorityLockable::unlock()
+{
+  bool notify_lp{false};
+  {
+    std::lock_guard<std::mutex> guard{parent_.cv_mutex_};
+    parent_.data_taken_ = false;
+    notify_lp = 0u == parent_.hp_waiting_count_;
+  }
+  if (notify_lp) {
+    parent_.lp_cv_.notify_one();
+  } else {
+    parent_.hp_cv_.notify_one();
+  }
+}
+
+HighPriorityLockable
+MutexTwoPriorities::get_high_priority_lockable()
+{
+  return HighPriorityLockable{*this};
+}
+
+LowPriorityLockable
+MutexTwoPriorities::get_low_priority_lockable()
+{
+  return LowPriorityLockable{*this};
+}
+
+}  // namespace detail
+}  // namespace rclcpp

rclcpp/src/rclcpp/executors/multi_threaded_executor.cpp

@@ -17,13 +17,19 @@
 #include <chrono>
 #include <functional>
 #include <memory>
+#include <unordered_map>
 #include <vector>
 
 #include "rclcpp/utilities.hpp"
 #include "rclcpp/scope_exit.hpp"
 
+using rclcpp::detail::MutexTwoPriorities;
 using rclcpp::executors::MultiThreadedExecutor;
 
+std::unordered_map<MultiThreadedExecutor *, std::shared_ptr<MutexTwoPriorities>>
+MultiThreadedExecutor::wait_mutex_set_;
+std::mutex MultiThreadedExecutor::shared_wait_mutex_;
+
 MultiThreadedExecutor::MultiThreadedExecutor(
   const rclcpp::ExecutorOptions & options,
   size_t number_of_threads,
@@ -33,6 +39,11 @@ MultiThreadedExecutor::MultiThreadedExecutor(
   yield_before_execute_(yield_before_execute),
   next_exec_timeout_(next_exec_timeout)
 {
+  {
+    std::lock_guard<std::mutex> wait_lock(
+      MultiThreadedExecutor::shared_wait_mutex_);
+    wait_mutex_set_[this] = std::make_shared<MutexTwoPriorities>();
+  }
   number_of_threads_ = number_of_threads ? number_of_threads : std::thread::hardware_concurrency();
   if (number_of_threads_ == 0) {
     number_of_threads_ = 1;
@@ -51,7 +62,9 @@ MultiThreadedExecutor::spin()
   std::vector<std::thread> threads;
   size_t thread_id = 0;
   {
-    std::lock_guard<std::mutex> wait_lock(wait_mutex_);
+    auto wait_mutex = MultiThreadedExecutor::wait_mutex_set_[this];
+    auto low_priority_wait_mutex = wait_mutex->get_low_priority_lockable();
+    std::lock_guard<MutexTwoPriorities::LowPriorityLockable> wait_lock(low_priority_wait_mutex);
     for (; thread_id < number_of_threads_ - 1; ++thread_id) {
       auto func = std::bind(&MultiThreadedExecutor::run, this, thread_id);
       threads.emplace_back(func);
@@ -76,7 +89,9 @@ MultiThreadedExecutor::run(size_t)
   while (rclcpp::ok(this->context_) && spinning.load()) {
     rclcpp::AnyExecutable any_exec;
     {
-      std::lock_guard<std::mutex> wait_lock(wait_mutex_);
+      auto wait_mutex = MultiThreadedExecutor::wait_mutex_set_[this];
+      auto low_priority_wait_mutex = wait_mutex->get_low_priority_lockable();
+      std::lock_guard<MutexTwoPriorities::LowPriorityLockable> wait_lock(low_priority_wait_mutex);
       if (!rclcpp::ok(this->context_) || !spinning.load()) {
         return;
       }
@@ -103,7 +118,9 @@ MultiThreadedExecutor::run(size_t)
     execute_any_executable(any_exec);
 
     if (any_exec.timer) {
-      std::lock_guard<std::mutex> wait_lock(wait_mutex_);
+      auto wait_mutex = MultiThreadedExecutor::wait_mutex_set_[this];
+      auto high_priority_wait_mutex = wait_mutex->get_high_priority_lockable();
+      std::lock_guard<MutexTwoPriorities::HighPriorityLockable> wait_lock(high_priority_wait_mutex);
       auto it = scheduled_timers_.find(any_exec.timer);
       if (it != scheduled_timers_.end()) {
         scheduled_timers_.erase(it);