2 files changed, 42 insertions, 62 deletions

diff --git a/include/framework/scheduling/Task.h b/include/framework/scheduling/Task.h
index 197e8bf..1591909 100644
--- a/include/framework/scheduling/Task.h
+++ b/include/framework/scheduling/Task.h
@@ -32,7 +32,7 @@ enum class ReconstructionPriority {
 template <ShardInterface ShardType, QueryInterface<ShardType> QueryType>
 struct ReconstructionArgs {
   typedef typename ShardType::RECORD RecordType;
-  std::atomic<std::shared_ptr<Version<ShardType, QueryType>>> version;
+  std::shared_ptr<Version<ShardType, QueryType>> version;
   ReconstructionVector tasks;
   void *extension;
   ReconstructionPriority priority;
diff --git a/include/framework/scheduling/Version.h b/include/framework/scheduling/Version.h
index 2b2b5ba..8d3d038 100644
--- a/include/framework/scheduling/Version.h
+++ b/include/framework/scheduling/Version.h
@@ -20,30 +20,21 @@ template <ShardInterface ShardType, QueryInterface<ShardType> QueryType>
 class Version {
 private:
   typedef typename ShardType::RECORD RecordType;
-  typedef MutableBuffer<RecordType> Buffer;
-  typedef ExtensionStructure<ShardType, QueryType> Structure;
-  typedef BufferView<RecordType> BufView;
+  typedef MutableBuffer<RecordType> BufferType;
+  typedef ExtensionStructure<ShardType, QueryType> StructureType;
+  typedef BufferView<RecordType> BufferViewType;
 
 public:
-  Version(size_t number = 0)
-      : m_buffer(nullptr), m_structure(nullptr), m_active_merge(false),
-        m_epoch_number(number), m_buffer_head(0) {}
-
-  Version(size_t number, Structure *structure, Buffer *buff, size_t head)
-      : m_buffer(buff), m_structure(structure), m_active_merge(false),
-        m_epoch_number(number), m_buffer_head(head) {
-    structure->take_reference();
-  }
+  Version(size_t vid = 0)
+      : m_buffer(nullptr), m_structure(nullptr), m_id(vid), m_buffer_head(0),
+        m_pending_buffer_head(-1) {}
 
-  ~Version() {
-    if (m_structure) {
-      m_structure->release_reference();
-    }
+  Version(size_t number, std::unique_ptr<StructureType> structure, BufferType *buff,
+          size_t head)
+      : m_buffer(buff), m_structure(std::move(structure)), m_id(number),
+        m_buffer_head(head), m_pending_buffer_head(-1) {}
 
-    if (m_structure->get_reference_count() == 0) {
-      delete m_structure;
-    }
-  }
+  ~Version() = default;
 
   /*
    * Versions are *not* copyable or movable. Only one can exist, and all users
@@ -54,13 +45,26 @@ public:
   Version &operator=(const Version &) = delete;
   Version &operator=(Version &&) = delete;
 
-  size_t get_epoch_number() const { return m_epoch_number; }
+  size_t get_id() const { return m_id; }
+
+  void set_id(size_t id) { m_id = id;}
 
-  const Structure *get_structure() const { return m_structure.get(); }
+  const StructureType *get_structure() const { return m_structure.get(); }
 
-  Structure *get_mutable_structure() { return m_structure.get(); }
+  StructureType *get_mutable_structure() { return m_structure.get(); }
 
-  BufView get_buffer() const { return m_buffer->get_buffer_view(m_buffer_head); }
+  bool set_structure(std::unique_ptr<StructureType> new_struct) {
+    if (m_structure) {
+      return false;
+    }
+
+    m_structure = std::move(new_struct);
+    return true;
+  }
+
+  BufferViewType get_buffer() const {
+    return m_buffer->get_buffer_view(m_buffer_head);
+  }
 
   /*
    * Returns a new Version object that is a copy of this one. The new object
@@ -69,54 +73,29 @@ public:
    * provided argument.
    */
   Version *clone(size_t number) {
-    std::unique_lock<std::mutex> m_buffer_lock;
-    auto epoch = new Version(number);
-    epoch->m_buffer = m_buffer;
-    epoch->m_buffer_head = m_buffer_head;
+    auto version = new Version(number);
+    version->m_buffer = m_buffer;
+    version->m_buffer_head = m_buffer_head;
 
     if (m_structure) {
-      epoch->m_structure = m_structure->copy();
-      /* the copy routine returns a structure with 0 references */
-      epoch->m_structure->take_reference();
+      version->m_structure = std::unique_ptr(m_structure->copy());
     }
 
-    return epoch;
+    return version;
   }
 
-  /*
-   * Check if a merge can be started from this Version. At present, without
-   * concurrent merging, this simply checks if there is currently a scheduled
-   * merge based on this Version. If there is, returns false. If there isn't,
-   * return true and set a flag indicating that there is an active merge.
-   */
-  bool prepare_reconstruction() {
-    auto old = m_active_merge.load();
-    if (old) {
-      return false;
-    }
-
-    // FIXME: this needs cleaned up
-    while (!m_active_merge.compare_exchange_strong(old, true)) {
-      old = m_active_merge.load();
-      if (old) {
-        return false;
-      }
-    }
-
-    return true;
+  void set_next_buffer_head(size_t new_head) {
+    m_pending_buffer_head = new_head;
   }
 
-  bool advance_buffer_head(size_t head) {
-    m_buffer_head = head;
+  bool advance_buffer_head() {
+    m_buffer_head = m_pending_buffer_head;
     return m_buffer->advance_head(m_buffer_head);
   }
 
 private:
-  Buffer *m_buffer;
-  std::unique_ptr<Structure> m_structure;
-
-  std::mutex m_buffer_lock;
-  std::atomic<bool> m_active_merge;
+  BufferType *m_buffer;
+  std::unique_ptr<StructureType> m_structure;
 
   /*
    * The number of currently active jobs
@@ -124,7 +103,8 @@ private:
    * epoch. An epoch can only be retired
    * when this number is 0.
    */
-  size_t m_epoch_number;
+  size_t m_id;
   size_t m_buffer_head;
+  ssize_t m_pending_buffer_head;
 };
 } // namespace de