From d2279e1b96d352a0af1d425dcaaf93e8a26a8d52 Mon Sep 17 00:00:00 2001
From: Douglas Rumbaugh <dbr4@psu.edu>
Date: Mon, 30 Oct 2023 17:15:05 -0400
Subject: General Comment + Consistency updates

---
 include/framework/DynamicExtension.h | 46 +++++++++++++++++++++---------------
 1 file changed, 27 insertions(+), 19 deletions(-)

(limited to 'include/framework/DynamicExtension.h')

diff --git a/include/framework/DynamicExtension.h b/include/framework/DynamicExtension.h
index f2bbacc..9129060 100644
--- a/include/framework/DynamicExtension.h
+++ b/include/framework/DynamicExtension.h
@@ -1,7 +1,7 @@
 /*
  * include/framework/DynamicExtension.h
  *
- * Copyright (C) 2023 Douglas Rumbaugh <drumbaugh@psu.edu> 
+ * Copyright (C) 2023 Douglas B. Rumbaugh <drumbaugh@psu.edu> 
  *                    Dong Xie <dongx@psu.edu>
  *
  * All rights reserved. Published under the Modified BSD License.
@@ -107,8 +107,7 @@ public:
     }
 
     size_t get_record_count() {
-        auto epoch = get_active_epoch();
-        epoch->start_job();
+        auto epoch = get_active_epoch_protected();
         auto t =  epoch->get_buffer_view().get_record_count() + epoch->get_structure()->get_record_count();
         epoch->end_job();
 
@@ -116,8 +115,7 @@ public:
     }
 
     size_t get_tombstone_count() {
-        auto epoch = get_active_epoch();
-        epoch->start_job();
+        auto epoch = get_active_epoch_protected();
         auto t = epoch->get_buffer_view().get_tombstone_count() + epoch->get_structure()->get_tombstone_count();
         epoch->end_job();
 
@@ -129,8 +127,7 @@ public:
     }
 
     size_t get_memory_usage() {
-        auto epoch = get_active_epoch();
-        epoch->start_job();
+        auto epoch = get_active_epoch_protected();
         auto t= epoch->get_buffer_view().get_memory_usage() + epoch->get_structure()->get_memory_usage();
         epoch->end_job();
 
@@ -138,8 +135,7 @@ public:
     }
 
     size_t get_aux_memory_usage() {
-        auto epoch = get_active_epoch();
-        epoch->start_job();
+        auto epoch = get_active_epoch_protected();
         auto t = epoch->get_buffer_view().get_aux_memory_usage() + epoch->get_structure()->get_aux_memory_usage();
         epoch->end_job();
 
@@ -151,9 +147,8 @@ public:
     }
     
     Shard *create_static_structure() {
-        auto epoch = get_active_epoch();
+        auto epoch = get_active_epoch_protected();
         auto bv = epoch->get_buffer_view();
-        epoch->start_job();
 
         auto vers = epoch->get_structure();
         std::vector<Shard *> shards;
@@ -219,6 +214,11 @@ private:
         return m_epochs[m_current_epoch.load()];
     }
 
+    _Epoch *get_active_epoch_protected() {
+        m_epochs[m_current_epoch.load()]->start_job();
+        return m_epochs[m_current_epoch.load()];
+    }
+
     void advance_epoch() {
         size_t new_epoch_num = m_current_epoch.load() + 1;
         _Epoch *new_epoch = m_epochs[new_epoch_num];
@@ -241,6 +241,12 @@ private:
      * structure will be a shallow copy of the old one's. 
      */
     _Epoch *create_new_epoch() {
+        /*
+         * This epoch access is _not_ protected under the assumption that
+         * only one merge will be able to trigger at a time. If that condition
+         * is violated, it is possible that this code will clone a retired
+         * epoch.
+         */
         auto new_epoch = get_active_epoch()->clone();
         std::unique_lock<std::mutex> m_struct_lock;
         m_versions.insert(new_epoch->get_structure());
@@ -311,6 +317,8 @@ private:
         MergeArgs<R, S, Q, L> *args = (MergeArgs<R, S, Q, L> *) arguments;
 
         Structure *vers = args->epoch->get_structure();
+        // FIXME: with an improved shard interface, multiple full buffers
+        //        could be merged at once here.
         Buffer *buff = (Buffer *) args->epoch->get_buffers()[0];
 
         for (ssize_t i=args->merges.size() - 1; i>=0; i--) {
@@ -387,24 +395,23 @@ private:
     }
 
     std::future<std::vector<R>> schedule_query(void *query_parms) {
-        auto epoch = get_active_epoch();
-        epoch->start_job();
+        auto epoch = get_active_epoch_protected();
         
         QueryArgs<R, S, Q, L> *args = new QueryArgs<R, S, Q, L>();
         args->epoch = epoch;
         args->query_parms = query_parms;
+        auto result = args->result_set.get_future();
+
         m_sched.schedule_job(async_query, 0, args);
 
-        return args->result_set.get_future();
+        return result;
     }
 
     int internal_append(const R &rec, bool ts) {
         Buffer *buffer = nullptr;
         do {
-            auto epoch = get_active_epoch();
-
-            while (!(buffer = epoch->get_active_buffer()))
-                ;
+            auto epoch = get_active_epoch_protected();
+            buffer = epoch->get_active_buffer();
             
             /* if the buffer is full, schedule a merge and add a new empty buffer */
             if (buffer->is_full()) {
@@ -413,7 +420,8 @@ private:
                 schedule_merge();
                 buffer = add_empty_buffer(epoch);
             }
-
+            // FIXME: not exactly the best spot for this
+            epoch->end_job();
         } while(!buffer->append(rec, ts));
 
         /* internal append should always succeed, eventually */
-- 
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