Let AtFork accept ptr-to-const handle

Summary: [Folly] Let `AtFork` accept ptr-to-`const` handle rather than requiring only ptr-to-non-`const`.

Reviewed By: luciang

Differential Revision: D19208255

fbshipit-source-id: c7a6ab42b7b652ebc4ea6465f80db37ef1d155df

folly/detail/AtFork.cpp

@@ -31,7 +31,7 @@ namespace detail {
 namespace {
 
 struct AtForkTask {
-  void* handle;
+  void const* handle;
   folly::Function<bool()> prepare;
   folly::Function<void()> parent;
   folly::Function<void()> child;
@@ -115,7 +115,7 @@ void AtFork::init() {
 }
 
 void AtFork::registerHandler(
-    void* handle,
+    void const* handle,
     folly::Function<bool()> prepare,
     folly::Function<void()> parent,
     folly::Function<void()> child) {
@@ -124,7 +124,7 @@ void AtFork::registerHandler(
       {handle, std::move(prepare), std::move(parent), std::move(child)});
 }
 
-void AtFork::unregisterHandler(void* handle) {
+void AtFork::unregisterHandler(void const* handle) {
   if (!handle) {
     return;
   }

folly/detail/AtFork.h

@@ -25,11 +25,11 @@ namespace detail {
 struct AtFork {
   static void init();
   static void registerHandler(
-      void* handle,
+      void const* handle,
       folly::Function<bool()> prepare,
       folly::Function<void()> parent,
       folly::Function<void()> child);
-  static void unregisterHandler(void* handle);
+  static void unregisterHandler(void const* handle);
 };
 
 } // namespace detail