1 files changed, 143 insertions, 0 deletions
diff --git a/include/framework/scheduling/Epoch.h b/include/framework/scheduling/Epoch.h
new file mode 100644
index 0000000..9377fb0
--- /dev/null
+++ b/include/framework/scheduling/Epoch.h
@@ -0,0 +1,143 @@
+/*
+ * include/framework/scheduling/Epoch.h
+ *
+ * Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu> 
+ *
+ * Distributed under the Modified BSD License.
+ *
+ */
+#pragma once
+
+#include <condition_variable>
+#include <mutex>
+
+#include "framework/structure/MutableBuffer.h"
+#include "framework/structure/ExtensionStructure.h"
+#include "framework/structure/BufferView.h"
+
+namespace de {
+
+
+template <RecordInterface R, ShardInterface<R> S, QueryInterface<R, S> Q, LayoutPolicy L>
+class Epoch {
+private:
+    typedef MutableBuffer<R> Buffer;
+    typedef ExtensionStructure<R, S, Q, L> Structure;
+    typedef BufferView<R> BufView;
+public:
+    Epoch(size_t number=0)
+        : m_buffer(nullptr)
+        , m_structure(nullptr)
+        , m_active_merge(false)
+        , m_epoch_number(number)
+        , m_buffer_head(0)
+    {}
+
+    Epoch(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();
+    }
+
+    ~Epoch() {
+        if (m_structure) {
+            m_structure->release_reference();
+        }
+
+        if (m_structure->get_reference_count() == 0) {
+            delete m_structure;
+        }
+
+    }
+
+    /*
+     * Epochs are *not* copyable or movable. Only one can exist, and all users
+     * of it work with pointers
+     */
+    Epoch(const Epoch&) = delete;
+    Epoch(Epoch&&) = delete;
+    Epoch &operator=(const Epoch&) = delete;
+    Epoch &operator=(Epoch&&) = delete;
+
+    size_t get_epoch_number() {
+        return m_epoch_number;
+    }
+
+    Structure *get_structure() {
+        return m_structure;
+    }
+
+    BufView get_buffer() {
+        return m_buffer->get_buffer_view(m_buffer_head);
+    }
+
+    /*
+     * Returns a new Epoch object that is a copy of this one. The new object
+     * will also contain a copy of the m_structure, rather than a reference to
+     * the same one. The epoch number of the new epoch will be set to the
+     * provided argument.
+     */
+    Epoch *clone(size_t number) {
+        std::unique_lock<std::mutex> m_buffer_lock;
+        auto epoch = new Epoch(number);
+        epoch->m_buffer = m_buffer;
+        epoch->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();
+        }
+
+        return epoch;
+    }
+
+    /*
+     * Check if a merge can be started from this Epoch. At present, without
+     * concurrent merging, this simply checks if there is currently a scheduled
+     * merge based on this Epoch. 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;
+    }
+
+    bool advance_buffer_head(size_t head) {
+        m_buffer_head = head;
+        return m_buffer->advance_head(m_buffer_head);
+    }
+
+private:
+    Structure *m_structure;
+    Buffer *m_buffer;
+
+    std::mutex m_buffer_lock;
+    std::atomic<bool> m_active_merge;
+
+    /*
+     * The number of currently active jobs
+     * (queries/merges) operating on this
+     * epoch. An epoch can only be retired
+     * when this number is 0.
+     */
+    size_t m_epoch_number;
+    size_t m_buffer_head;
+};
+}