VirtualExecutor

Summary:
Executor adaptor which allows joining only tasks scheduled through this VirtualExecutor instance without joining all other tasks in a wrapped Executor.
This is very similar to VirtualEventBase, but works for any Executor.

Reviewed By: yfeldblum, aary

Differential Revision: D8342064

fbshipit-source-id: 420b6390e2da88c4826e6d22bc8f3b3585525214

folly/VirtualExecutor.h

+/*
+ * Copyright 2018-present Facebook, 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.
+ */
+
+#pragma once
+
+#include <folly/DefaultKeepAliveExecutor.h>
+
+namespace folly {
+
+/**
+ * VirtualExecutor implements a light-weight view onto existing Executor.
+ *
+ * Multiple VirtualExecutors can be backed by a single Executor.
+ *
+ * VirtualExecutor's destructor blocks until all tasks scheduled through it are
+ * complete. Executor's destructor also blocks until all VirtualExecutors
+ * backed by it are released.
+ */
+class VirtualExecutor : public DefaultKeepAliveExecutor {
+ public:
+  explicit VirtualExecutor(KeepAlive<> executor)
+      : executor_(std::move(executor)) {}
+
+  explicit VirtualExecutor(Executor* executor)
+      : VirtualExecutor(getKeepAliveToken(executor)) {}
+
+  explicit VirtualExecutor(Executor& executor)
+      : VirtualExecutor(getKeepAliveToken(executor)) {}
+
+  VirtualExecutor(const VirtualExecutor&) = delete;
+  VirtualExecutor& operator=(const VirtualExecutor&) = delete;
+
+  uint8_t getNumPriorities() const override {
+    return executor_->getNumPriorities();
+  }
+
+  void add(Func f) override {
+    executor_->add([func = std::move(f),
+                    me = getKeepAliveToken(this)]() mutable { func(); });
+  }
+
+  void addWithPriority(Func f, int8_t priority) override {
+    executor_->addWithPriority(
+        [func = std::move(f), me = getKeepAliveToken(this)]() mutable {
+          func();
+        },
+        priority);
+  }
+
+  ~VirtualExecutor() override {
+    joinKeepAlive();
+  }
+
+ private:
+  const KeepAlive<> executor_;
+};
+
+} // namespace folly

folly/executors/test/ThreadPoolExecutorTest.cpp

@@ -18,6 +18,7 @@
 #include <thread>
 
 #include <folly/Exception.h>
+#include <folly/VirtualExecutor.h>
 #include <folly/executors/CPUThreadPoolExecutor.h>
 #include <folly/executors/FutureExecutor.h>
 #include <folly/executors/IOThreadPoolExecutor.h>
@@ -313,14 +314,16 @@ TEST(ThreadPoolExecutorTest, PriorityPreemptionTest) {
     completed++;
   };
   CPUThreadPoolExecutor pool(0, 2);
+  {
+    VirtualExecutor ve(pool);
     for (int i = 0; i < 50; i++) {
-    pool.addWithPriority(lopri, Executor::LO_PRI);
+      ve.addWithPriority(lopri, Executor::LO_PRI);
     }
     for (int i = 0; i < 50; i++) {
-    pool.addWithPriority(hipri, Executor::HI_PRI);
+      ve.addWithPriority(hipri, Executor::HI_PRI);
     }
     pool.setNumThreads(1);
-  pool.join();
+  }
   EXPECT_EQ(100, completed);
 }
 
@@ -751,6 +754,33 @@ static void WeakRefTest() {
   EXPECT_EQ(1, counter);
 }
 
+template <typename TPE>
+static void virtualExecutorTest() {
+  using namespace std::literals;
+
+  folly::Optional<folly::SemiFuture<folly::Unit>> f;
+  int counter{0};
+  {
+    TPE fe(1);
+    {
+      VirtualExecutor ve(fe);
+      f = futures::sleep(100ms)
+              .via(&ve)
+              .then([&] {
+                ++counter;
+                return futures::sleep(100ms);
+              })
+              .via(&fe)
+              .then([&] { ++counter; })
+              .semi();
+    }
+    EXPECT_EQ(1, counter);
+  }
+  EXPECT_TRUE(f->isReady());
+  EXPECT_NO_THROW(std::move(*f).get());
+  EXPECT_EQ(2, counter);
+}
+
 TEST(ThreadPoolExecutorTest, WeakRefTestIO) {
   WeakRefTest<IOThreadPoolExecutor>();
 }
@@ -758,3 +788,11 @@ TEST(ThreadPoolExecutorTest, WeakRefTestIO) {
 TEST(ThreadPoolExecutorTest, WeakRefTestCPU) {
   WeakRefTest<CPUThreadPoolExecutor>();
 }
+
+TEST(ThreadPoolExecutorTest, VirtualExecutorTestIO) {
+  virtualExecutorTest<IOThreadPoolExecutor>();
+}
+
+TEST(ThreadPoolExecutorTest, VirtualExecutorTestCPU) {
+  virtualExecutorTest<CPUThreadPoolExecutor>();
+}