LifoSem make tryRemoveNode protected

Summary:
Lifo sem exposes allocateNode and tryWaitOrPush as protected which allows inherited classes custom Node implementation, creation and enqueueing.
tryRemoveNode was private which prevented inherited classes from dequeueing a Node without signaling shutdown.
This diff fixes it

Reviewed By: shixiao

Differential Revision: D15647287

fbshipit-source-id: 5b26a9616f6de559224f9d8c38230780c78a7cf5

folly/synchronization/LifoSem.h

@@ -594,18 +594,6 @@ struct LifoSemBase {
     return decrOrPush(n, nodeToIdx(waiterNode));
   }
 
- private:
-  CachelinePadded<folly::AtomicStruct<LifoSemHead, Atom>> head_;
-
-  static LifoSemNode<Handoff, Atom>& idxToNode(uint32_t idx) {
-    auto raw = &LifoSemRawNode<Atom>::pool()[idx];
-    return *static_cast<LifoSemNode<Handoff, Atom>*>(raw);
-  }
-
-  static uint32_t nodeToIdx(const LifoSemNode<Handoff, Atom>& node) {
-    return LifoSemRawNode<Atom>::pool().locateElem(&node);
-  }
-
   // Locks the list head (blocking concurrent pushes and pops)
   // and attempts to remove this node.  Returns true if node was
   // found and removed, false if not found.
@@ -660,6 +648,18 @@ struct LifoSemBase {
     return result;
   }
 
+ private:
+  CachelinePadded<folly::AtomicStruct<LifoSemHead, Atom>> head_;
+
+  static LifoSemNode<Handoff, Atom>& idxToNode(uint32_t idx) {
+    auto raw = &LifoSemRawNode<Atom>::pool()[idx];
+    return *static_cast<LifoSemNode<Handoff, Atom>*>(raw);
+  }
+
+  static uint32_t nodeToIdx(const LifoSemNode<Handoff, Atom>& node) {
+    return LifoSemRawNode<Atom>::pool().locateElem(&node);
+  }
+
   /// Either increments by n and returns 0, or pops a node and returns it.
   /// If n + the stripe's value overflows, then the stripe's value
   /// saturates silently at 2^32-1