no shared_ptr in EventBaseLocal

Summary: [folly] no `shared_ptr` storage in `EventBaseLocal` since its refcount operations are unnecessary. Pare it down to `unique_ptr` with a straightforward fun-ptr deleter.

Reviewed By: iahs

Differential Revision: D26246619

fbshipit-source-id: 3d0214ccb6c4730ca7b573065b4468a0dce85d40

folly/io/async/EventBase.h

@@ -35,6 +35,7 @@
 
 #include <folly/Executor.h>
 #include <folly/Function.h>
+#include <folly/Memory.h>
 #include <folly/Portability.h>
 #include <folly/ScopeGuard.h>
 #include <folly/Synchronized.h>
@@ -948,7 +949,7 @@ class EventBase : public TimeoutManager,
   friend class detail::EventBaseLocalBase;
   template <typename T>
   friend class EventBaseLocal;
-  std::unordered_map<std::size_t, std::shared_ptr<void>> localStorage_;
+  std::unordered_map<std::size_t, erased_unique_ptr> localStorage_;
   std::unordered_set<detail::EventBaseLocalBaseBase*> localStorageToDtor_;
 
   folly::once_flag virtualEventBaseInitFlag_;

folly/io/async/EventBaseLocal.cpp

@@ -20,6 +20,7 @@
 #include <thread>
 
 #include <folly/MapUtil.h>
+#include <folly/Memory.h>
 
 namespace folly {
 namespace detail {
@@ -56,12 +57,17 @@ void EventBaseLocalBase::onEventBaseDestruction(EventBase& evb) {
   eventBases_.wlock()->erase(&evb);
 }
 
-void EventBaseLocalBase::setVoid(EventBase& evb, std::shared_ptr<void>&& ptr) {
+void EventBaseLocalBase::setVoid(
+    EventBase& evb, void* ptr, void (*dtor)(void*)) {
+  // construct the unique-ptr eagerly, just in case anything between this and
+  // the emplace below could throw
+  auto erased = erased_unique_ptr{ptr, dtor};
+
   evb.dcheckIsInEventBaseThread();
 
   auto alreadyExists = evb.localStorage_.find(key_) != evb.localStorage_.end();
 
-  evb.localStorage_.emplace(key_, std::move(ptr));
+  evb.localStorage_.emplace(key_, std::move(erased));
 
   if (!alreadyExists) {
     eventBases_.wlock()->insert(&evb);

folly/io/async/EventBaseLocal.h

@@ -38,7 +38,7 @@ class EventBaseLocalBase : public EventBaseLocalBaseBase {
   void onEventBaseDestruction(EventBase& evb) override;
 
  protected:
-  void setVoid(EventBase& evb, std::shared_ptr<void>&& ptr);
+  void setVoid(EventBase& evb, void* ptr, void (*dtor)(void*));
   void* getVoid(EventBase& evb);
 
   folly::Synchronized<std::unordered_set<EventBase*>> eventBases_;
@@ -81,16 +81,14 @@ class EventBaseLocal : public detail::EventBaseLocalBase {
 
   void emplace(EventBase& evb, T* ptr) {
     DCHECK(ptr != nullptr);
-    std::shared_ptr<T> smartPtr(ptr);
-    setVoid(evb, std::move(smartPtr));
+    setVoid(evb, ptr, detail::thunk::ruin<T>);
   }
 
   template <typename... Args>
   T& emplace(EventBase& evb, Args&&... args) {
-    auto smartPtr = std::make_shared<T>(std::forward<Args>(args)...);
-    auto& ref = *smartPtr;
-    setVoid(evb, std::move(smartPtr));
-    return ref;
+    auto ptr = new T(static_cast<Args&&>(args)...);
+    setVoid(evb, ptr, detail::thunk::ruin<T>);
+    return *ptr;
   }
 
   template <typename... Args>
@@ -98,10 +96,9 @@ class EventBaseLocal : public detail::EventBaseLocalBase {
     if (auto ptr = getVoid(evb)) {
       return *static_cast<T*>(ptr);
     }
-    auto smartPtr = std::make_shared<T>(std::forward<Args>(args)...);
-    auto& ref = *smartPtr;
-    setVoid(evb, std::move(smartPtr));
-    return ref;
+    auto ptr = new T(static_cast<Args&&>(args)...);
+    setVoid(evb, ptr, detail::thunk::ruin<T>);
+    return *ptr;
   }
 
   template <typename Func>
@@ -112,10 +109,9 @@ class EventBaseLocal : public detail::EventBaseLocalBase {
     if (auto ptr = getVoid(evb)) {
       return *static_cast<T*>(ptr);
     }
-    auto smartPtr = std::shared_ptr<T>(new T(fn()));
-    auto& ref = *smartPtr;
-    setVoid(evb, std::move(smartPtr));
-    return ref;
+    auto ptr = new T(fn());
+    setVoid(evb, ptr, detail::thunk::ruin<T>);
+    return *ptr;
   }
 };