Fix FunctionScheduler::resetFunctionTimer

Summary: Keeping moved out functions on the heap leads to segfaults. Let's fix that by calling make_heap each time we need to update. We will regress resetFunctionTimer complexity to O(n), which is exactly what it was before D5668557.

Reviewed By: simpkins

Differential Revision: D6822488

fbshipit-source-id: 94f75789b01ff85e2df271822b767160285462c3

folly/experimental/FunctionScheduler.cpp

@@ -303,13 +303,12 @@ bool FunctionScheduler::resetFunctionTimer(StringPiece nameID) {
   // fix the heap ordering if we adjust the key (nextRunTime) for the existing
   // RepeatFunc. Instead, we just cancel it and add an identical object.
   auto it = functionsMap_.find(nameID);
-
   if (it != functionsMap_.end() && it->second->isValid()) {
-    auto funcCopy = std::make_unique<RepeatFunc>(std::move(*(it->second)));
-    it->second->cancel();
-    // This will take care of making sure that functionsMap_[it->first] =
-    // funcCopy.
-    addFunctionToHeap(l, std::move(funcCopy));
+    if (running_) {
+      it->second->resetNextRunTime(steady_clock::now());
+      std::make_heap(functions_.begin(), functions_.end(), fnCmp_);
+      runningCondvar_.notify_one();
+    }
     return true;
   }
   return false;

folly/experimental/test/FunctionSchedulerTest.cpp

@@ -252,6 +252,23 @@ TEST(FunctionScheduler, ResetFunc) {
   EXPECT_EQ(12, total);
 }
 
+TEST(FunctionScheduler, ResetFunc2) {
+  int total = 0;
+  FunctionScheduler fs;
+  fs.addFunctionOnce([&] { total += 2; }, "add2", testInterval(1));
+  fs.addFunctionOnce([&] { total += 3; }, "add3", testInterval(1));
+  fs.start();
+  delay(2);
+  fs.addFunctionOnce([&] { total += 3; }, "add4", testInterval(2));
+  EXPECT_TRUE(fs.resetFunctionTimer("add4"));
+  fs.addFunctionOnce([&] { total += 3; }, "add6", testInterval(2));
+  delay(1);
+  EXPECT_TRUE(fs.resetFunctionTimer("add4"));
+  delay(2);
+  EXPECT_FALSE(fs.resetFunctionTimer("add3"));
+  fs.addFunctionOnce([&] { total += 3; }, "add4", testInterval(1));
+}
+
 TEST(FunctionScheduler, ResetFuncWhileRunning) {
   struct State {
     boost::barrier barrier_a{2};