FunctionScheduler - return whether shutdown was successful

Summary: We want to fail fast if we attempt to stop a scheduler that was not running

Reviewed By: yfeldblum

Differential Revision: D3976919

fbshipit-source-id: d8aa8b35aa9e22758e6a7ef64f48a7dd6d990b1c

folly/experimental/FunctionScheduler.cpp

@@ -277,17 +277,18 @@ bool FunctionScheduler::start() {
   return true;
 }
 
-void FunctionScheduler::shutdown() {
+bool FunctionScheduler::shutdown() {
   {
     std::lock_guard<std::mutex> g(mutex_);
     if (!running_) {
-      return;
+      return false;
     }
 
     running_ = false;
     runningCondvar_.notify_one();
   }
   thread_.join();
+  return true;
 }
 
 void FunctionScheduler::run() {

folly/experimental/FunctionScheduler.h

@@ -177,8 +177,9 @@ class FunctionScheduler {
    * Stops the FunctionScheduler.
    *
    * It may be restarted later by calling start() again.
+   * Returns false if the scheduler was not running.
    */
-  void shutdown();
+  bool shutdown();
 
   /**
    * Set the name of the worker thread.

folly/experimental/test/FunctionSchedulerTest.cpp

@@ -50,6 +50,19 @@ void delay(int n) {
 
 } // unnamed namespace
 
+TEST(FunctionScheduler, StartAndShutdown) {
+  FunctionScheduler fs;
+  EXPECT_TRUE(fs.start());
+  EXPECT_FALSE(fs.start());
+  EXPECT_TRUE(fs.shutdown());
+  EXPECT_FALSE(fs.shutdown());
+  // start again
+  EXPECT_TRUE(fs.start());
+  EXPECT_FALSE(fs.start());
+  EXPECT_TRUE(fs.shutdown());
+  EXPECT_FALSE(fs.shutdown());
+}
+
 TEST(FunctionScheduler, SimpleAdd) {
   int total = 0;
   FunctionScheduler fs;
@@ -76,7 +89,6 @@ TEST(FunctionScheduler, AddCancel) {
   delay(2);
   EXPECT_EQ(4, total);
   fs.addFunction([&] { total += 1; }, testInterval(2), "add2");
-  EXPECT_FALSE(fs.start()); // already running
   delay(1);
   EXPECT_EQ(5, total);
   delay(2);