logging: fix compiler compatibility for one more constexpr function

[folly.git] / folly / experimental / LockFreeRingBuffer.h

diff --git a/folly/experimental/LockFreeRingBuffer.h b/folly/experimental/LockFreeRingBuffer.h
index 0a2d10f3eaaa48659a412584670687cb7789c5e7..0e32e033ed716a22665c29e898b8f232672c1a22 100644 (file)
--- a/folly/experimental/LockFreeRingBuffer.h
+++ b/folly/experimental/LockFreeRingBuffer.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2015 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -18,15 +18,15 @@
 
 #include <atomic>
 #include <boost/noncopyable.hpp>
-#include <iostream>
 #include <cmath>
 #include <memory>
 #include <string.h>
 #include <type_traits>
-#include <unistd.h>
 
-#include <folly/detail/TurnSequencer.h>
 #include <folly/Portability.h>
+#include <folly/detail/TurnSequencer.h>
+#include <folly/portability/TypeTraits.h>
+#include <folly/portability/Unistd.h>
 
 namespace folly {
 namespace detail {
@@ -70,16 +70,24 @@ public:
   struct Cursor {
     explicit Cursor(uint64_t initialTicket) noexcept : ticket(initialTicket) {}
 
-    void moveForward(uint64_t steps = 1) noexcept {
+    /// Returns true if this cursor now points to a different
+    /// write, false otherwise.
+    bool moveForward(uint64_t steps = 1) noexcept {
+      uint64_t prevTicket = ticket;
       ticket += steps;
+      return prevTicket != ticket;
     }
 
-    void moveBackward(uint64_t steps = 1) noexcept {
+    /// Returns true if this cursor now points to a previous
+    /// write, false otherwise.
+    bool moveBackward(uint64_t steps = 1) noexcept {
+      uint64_t prevTicket = ticket;
       if (steps > ticket) {
         ticket = 0;
       } else {
         ticket -= steps;
       }
+      return prevTicket != ticket;
     }
 
   protected: // for test visibility reasons
@@ -195,7 +203,8 @@ public:
   bool waitAndTryRead(T& dest, uint32_t turn) noexcept {
     uint32_t desired_turn = (turn + 1) * 2;
     Atom<uint32_t> cutoff(0);
-    if(!sequencer_.tryWaitForTurn(desired_turn, cutoff, false)) {
+    if (sequencer_.tryWaitForTurn(desired_turn, cutoff, false) !=
+        TurnSequencer<Atom>::TryWaitResult::SUCCESS) {
       return false;
     }
     memcpy(&dest, &data, sizeof(T));