Fix AsyncioExecutor shutdown

Summary: It's unsafe to destroy the object before keepAlive reaches 0. We can still skip running the scheduled functions if those are unsafe to run.

Reviewed By: nanshu

Differential Revision: D19605152

fbshipit-source-id: b99c28dc65da2a5621ce5260491c13754fca03ad

folly/python/AsyncioExecutor.h

@@ -38,14 +38,10 @@ class AsyncioExecutor : public DrivableExecutor, public SequencedExecutor {
 
   ~AsyncioExecutor() override {
     keepAliveRelease();
-    if (!FOLLY_DETAIL_PY_ISFINALIZING()) {
-      // if Python is finalizing calling drive() WILL segfault.
-      // any code that could have been called is now inconsequential.
     while (keepAliveCounter_ > 0) {
       drive();
     }
   }
-  }
 
   void add(Func func) override {
     queue_.putMessage(std::move(func));
@@ -57,6 +53,11 @@ class AsyncioExecutor : public DrivableExecutor, public SequencedExecutor {
 
   void drive() noexcept override {
     consumer_.consumeUntilDrained([](Func&& func) {
+      if (FOLLY_DETAIL_PY_ISFINALIZING()) {
+        // if Python is finalizing calling scheduled functions MAY segfault.
+        // any code that could have been called is now inconsequential.
+        return;
+      }
       try {
         func();
       } catch (...) {