Use atomic _generation in vespalib::GenerationHandler.

2 files changed, 12 insertions, 10 deletions

diff --git a/vespalib/src/vespa/vespalib/util/generationhandler.cpp b/vespalib/src/vespa/vespalib/util/generationhandler.cpp
index 7797978d187..d1cc0271068 100644
--- a/vespalib/src/vespa/vespalib/util/generationhandler.cpp
+++ b/vespalib/src/vespa/vespalib/util/generationhandler.cpp
@@ -138,7 +138,7 @@ GenerationHandler::GenerationHandler()
 {
     _last = _first = new GenerationHold;
     ++_numHolds;
-    _first->_generation.store(_generation, std::memory_order_relaxed);
+    _first->_generation.store(getCurrentGeneration(), std::memory_order_relaxed);
     _first->setValid();
 }
 
@@ -188,7 +188,7 @@ GenerationHandler::incGeneration()
         // the typical case when no readers are present.
         // Note: atomic thread fence above is needed to avoid stale data in
         // reader
-        _generation = ngen;
+        set_generation(ngen);
         last->_generation.store(ngen, std::memory_order_relaxed);
         updateFirstUsedGeneration();
         return;
@@ -205,7 +205,7 @@ GenerationHandler::incGeneration()
     nhold->_next = nullptr;
     nhold->setValid();
     last->_next = nhold;
-    _generation = ngen;
+    set_generation(ngen);
     _last.store(nhold, std::memory_order_release);
     updateFirstUsedGeneration();
 }
@@ -213,7 +213,7 @@ GenerationHandler::incGeneration()
 uint32_t
 GenerationHandler::getGenerationRefCount(generation_t gen) const
 {
-    if (static_cast<sgeneration_t>(gen - _generation) > 0)
+    if (static_cast<sgeneration_t>(gen - getCurrentGeneration()) > 0)
         return 0u;
     if (static_cast<sgeneration_t>(getFirstUsedGeneration() - gen) > 0)
         return 0u;
diff --git a/vespalib/src/vespa/vespalib/util/generationhandler.h b/vespalib/src/vespa/vespalib/util/generationhandler.h
index 2aeb4c2f886..9637ad0e414 100644
--- a/vespalib/src/vespa/vespalib/util/generationhandler.h
+++ b/vespalib/src/vespa/vespalib/util/generationhandler.h
@@ -72,13 +72,15 @@ public:
     };
 
 private:
-    generation_t    _generation;
+    std::atomic<generation_t>     _generation;
     std::atomic<generation_t>     _firstUsedGeneration;
     std::atomic<GenerationHold *> _last;      // Points to "current generation" entry
     GenerationHold *_first;     // Points to "firstUsedGeneration" entry
     GenerationHold *_free;      // List of free entries
     uint32_t        _numHolds;  // Number of allocated generation hold entries
 
+    void set_generation(generation_t generation) noexcept { _generation.store(generation, std::memory_order_relaxed); }
+
 public:
     /**
      * Creates a new generation handler.
@@ -108,19 +110,19 @@ public:
      * Returns the first generation guarded by a reader.  It might be too low
      * if writer hasn't updated first used generation after last reader left.
      */
-    generation_t getFirstUsedGeneration() const {
+    generation_t getFirstUsedGeneration() const noexcept {
         return _firstUsedGeneration.load(std::memory_order_relaxed);
     }
 
     /**
      * Returns the current generation.
      **/
-    generation_t getCurrentGeneration() const {
-        return _generation;
+    generation_t getCurrentGeneration() const noexcept {
+        return _generation.load(std::memory_order_relaxed);
     }
 
-    generation_t getNextGeneration() const {
-        return _generation + 1;
+    generation_t getNextGeneration() const noexcept {
+        return getCurrentGeneration() + 1;
     }
 
     /**