Allow getting the sequence number of a token via a read only getter function

Summary: Allow getting the sequence number of a token via a read only getter function

Reviewed By: yfeldblum

Differential Revision: D4120900

fbshipit-source-id: b664dda29d13a1755e041ab9c33c0d7324690ba7

folly/fibers/AtomicBatchDispatcher-inl.h

@@ -148,6 +148,11 @@ AtomicBatchDispatcher<InputT, ResultT>::Token::Token(
     size_t sequenceNumber)
     : baton_(std::move(baton)), sequenceNumber_(sequenceNumber) {}
 
+template <typename InputT, typename ResultT>
+size_t AtomicBatchDispatcher<InputT, ResultT>::Token::sequenceNumber() const {
+  return sequenceNumber_;
+}
+
 template <typename InputT, typename ResultT>
 Future<ResultT> AtomicBatchDispatcher<InputT, ResultT>::Token::dispatch(
     InputT input) {

folly/fibers/AtomicBatchDispatcher.h

@@ -147,6 +147,8 @@ class AtomicBatchDispatcher {
     Token(Token&&) = default;
     Token& operator=(Token&&) = default;
 
+    size_t sequenceNumber() const;
+
    private:
     // Disallow copying a Token object
     Token(const Token&) = delete;