Make ExecutorLoopController cancel local callback in destructor

Summary: EventBaseLoopController does this already. This way it's safe to destroy FiberManager even if some local callback is left in the executor.

Differential Revision: D26563934

fbshipit-source-id: 0845e5c532634fa9c53694cd67e983886cea82de

folly/fibers/ExecutorLoopController-inl.h

@@ -36,7 +36,16 @@ inline void ExecutorLoopController::schedule() {
   if (!executorKeepAlive_) {
     executorKeepAlive_ = getKeepAliveToken(executor_);
   }
-  executor_->add([this]() { return runLoop(); });
+  auto guard = localCallbackControlBlock_->trySchedule();
+  if (!guard) {
+    return;
+  }
+  executor_->add([this, guard = std::move(guard)]() {
+    if (guard->isCancelled()) {
+      return;
+    }
+    runLoop();
+  });
 }
 
 inline void ExecutorLoopController::runLoop() {

folly/fibers/ExecutorLoopController.h

@@ -86,6 +86,51 @@ class ExecutorLoopController : public fibers::ExecutorBasedLoopController {
   ExecutorTimeoutManager timeoutManager_;
   HHWheelTimer::UniquePtr timer_;
 
+  class LocalCallbackControlBlock {
+   public:
+    struct DeleteOrCancel {
+      void operator()(LocalCallbackControlBlock* controlBlock) {
+        if (controlBlock->scheduled_) {
+          controlBlock->cancelled_ = true;
+        } else {
+          delete controlBlock;
+        }
+      }
+    };
+    using Ptr = std::unique_ptr<LocalCallbackControlBlock, DeleteOrCancel>;
+
+    struct GuardDeleter {
+      void operator()(LocalCallbackControlBlock* controlBlock) {
+        DCHECK(controlBlock->scheduled_);
+        controlBlock->scheduled_ = false;
+        if (controlBlock->cancelled_) {
+          delete controlBlock;
+        }
+      }
+    };
+    using Guard = std::unique_ptr<LocalCallbackControlBlock, GuardDeleter>;
+
+    static Ptr create() { return Ptr(new LocalCallbackControlBlock()); }
+
+    Guard trySchedule() {
+      if (scheduled_) {
+        return {};
+      }
+      scheduled_ = true;
+      return Guard(this);
+    }
+
+    bool isCancelled() const { return cancelled_; }
+
+   private:
+    LocalCallbackControlBlock() {}
+
+    bool cancelled_{false};
+    bool scheduled_{false};
+  };
+  LocalCallbackControlBlock::Ptr localCallbackControlBlock_{
+      LocalCallbackControlBlock::create()};
+
   void setFiberManager(fibers::FiberManager* fm) override;
   void schedule() override;
   void runLoop() override;

folly/python/fiber_manager.pyx

@@ -46,8 +46,6 @@ cdef class FiberManager:
     def __dealloc__(FiberManager self):
         while deref(self.cManager).hasTasks():
             self.cExecutor.drive()
-        # drive one last time
-        self.cExecutor.drive()
 
         # Explicitly reset here, otherwise it is possible
         # that self.cManager dstor runs after python finalizes