folly/executors/GlobalExecutor.cpp

   1 /*
   2  * Copyright 2017-present Facebook, Inc.
   3  *
   4  * Licensed under the Apache License, Version 2.0 (the "License");
   5  * you may not use this file except in compliance with the License.
   6  * You may obtain a copy of the License at
   7  *
   8  *   http://www.apache.org/licenses/LICENSE-2.0
   9  *
  10  * Unless required by applicable law or agreed to in writing, software
  11  * distributed under the License is distributed on an "AS IS" BASIS,
  12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  13  * See the License for the specific language governing permissions and
  14  * limitations under the License.
  15  */
  16
  17 #include <memory>
  18 #include <thread>
  19
  20 #include <folly/Function.h>
  21 #include <folly/SharedMutex.h>
  22 #include <folly/Singleton.h>
  23 #include <folly/executors/IOExecutor.h>
  24 #include <folly/executors/IOThreadPoolExecutor.h>
  25 #include <folly/executors/InlineExecutor.h>
  26
  27 using namespace folly;
  28
  29 namespace {
  30
  31 template <class ExecutorBase>
  32 class GlobalExecutor {
  33  public:
  34   explicit GlobalExecutor(
  35       Function<std::unique_ptr<ExecutorBase>()> constructDefault)
  36       : constructDefault_(std::move(constructDefault)) {}
  37
  38   std::shared_ptr<ExecutorBase> get() {
  39     {
  40       SharedMutex::ReadHolder guard(mutex_);
  41       if (auto executor = executor_.lock()) {
  42         return executor; // Fast path.
  43       }
  44     }
  45
  46     SharedMutex::WriteHolder guard(mutex_);
  47     if (auto executor = executor_.lock()) {
  48       return executor;
  49     }
  50
  51     if (!defaultExecutor_) {
  52       defaultExecutor_ = constructDefault_();
  53     }
  54
  55     return defaultExecutor_;
  56   }
  57
  58   void set(std::weak_ptr<ExecutorBase> executor) {
  59     SharedMutex::WriteHolder guard(mutex_);
  60     executor_.swap(executor);
  61   }
  62
  63  private:
  64   SharedMutex mutex_;
  65   std::weak_ptr<ExecutorBase> executor_;
  66   std::shared_ptr<ExecutorBase> defaultExecutor_;
  67   Function<std::unique_ptr<ExecutorBase>()> constructDefault_;
  68 };
  69
  70 Singleton<GlobalExecutor<Executor>> gGlobalCPUExecutor([] {
  71   return new GlobalExecutor<Executor>(
  72       // Default global CPU executor is an InlineExecutor.
  73       [] { return std::make_unique<InlineExecutor>(); });
  74 });
  75
  76 Singleton<GlobalExecutor<IOExecutor>> gGlobalIOExecutor([] {
  77   return new GlobalExecutor<IOExecutor>(
  78       // Default global IO executor is an IOThreadPoolExecutor.
  79       [] {
  80         return std::make_unique<IOThreadPoolExecutor>(
  81             std::thread::hardware_concurrency(),
  82             std::make_shared<NamedThreadFactory>("GlobalIOThreadPool"));
  83       });
  84 });
  85
  86 } // namespace
  87
  88 namespace folly {
  89
  90 std::shared_ptr<Executor> getCPUExecutor() {
  91   if (auto singleton = gGlobalCPUExecutor.try_get()) {
  92     return singleton->get();
  93   }
  94   return nullptr;
  95 }
  96
  97 void setCPUExecutor(std::weak_ptr<Executor> executor) {
  98   if (auto singleton = gGlobalCPUExecutor.try_get()) {
  99     singleton->set(std::move(executor));
 100   }
 101 }
 102
 103 std::shared_ptr<IOExecutor> getIOExecutor() {
 104   if (auto singleton = gGlobalIOExecutor.try_get()) {
 105     return singleton->get();
 106   }
 107   return nullptr;
 108 }
 109
 110 void setIOExecutor(std::weak_ptr<IOExecutor> executor) {
 111   if (auto singleton = gGlobalIOExecutor.try_get()) {
 112     singleton->set(std::move(executor));
 113   }
 114 }
 115
 116 EventBase* getEventBase() {
 117   return getIOExecutor()->getEventBase();
 118 }
 119
 120 } // namespace folly