Epoch/DynamicExtension: added cv to epoch retirement check

Instead of busy waiting on the active job count, a condition variable is
now used to wait for all active jobs to finish before freeing an epoch's
resources.

2 files changed, 36 insertions, 4 deletions

diff --git a/include/framework/DynamicExtension.h b/include/framework/DynamicExtension.h
index eb78d48..21d0261 100644
--- a/include/framework/DynamicExtension.h
+++ b/include/framework/DynamicExtension.h
@@ -79,6 +79,8 @@ public:
     }
 
     int erase(const R &rec) {
+        // FIXME: delete tagging will require a lot of extra work to get
+        //        operating "correctly" in a concurrent environment.
         if constexpr (D == DeletePolicy::TAGGING) {
             BufView buffers = get_active_epoch()->get_buffer_view();
 
@@ -118,6 +120,7 @@ public:
         epoch->start_job();
         auto t = epoch->get_buffer_view().get_tombstone_count() + epoch->get_structure()->get_tombstone_count();
         epoch->end_job();
+
         return t;
     }
 
@@ -271,11 +274,9 @@ private:
          * accumulate new active jobs. Eventually, this
          * number will hit zero and the function will
          * proceed.
-         *
-         * FIXME: this can be replaced with a cv, which
-         * is probably a superior solution in this case
          */
-        while (epoch->get_active_job_num() > 0) 
+
+        while (!epoch->retirable()) 
             ;
 
         /*
diff --git a/include/framework/scheduling/Epoch.h b/include/framework/scheduling/Epoch.h
index fe63c86..87463bd 100644
--- a/include/framework/scheduling/Epoch.h
+++ b/include/framework/scheduling/Epoch.h
@@ -62,6 +62,11 @@ public:
 
     void end_job() {
         m_active_jobs.fetch_add(-1);
+
+        if (m_active_jobs.load() == 0) {
+            std::unique_lock<std::mutex> lk(m_cv_lock);
+            m_active_cv.notify_all();  
+        }
     }
 
     size_t get_active_job_num() {
@@ -115,10 +120,35 @@ public:
         return epoch;
     }
 
+    /*
+     * 
+     */
+    bool retirable() {
+        /* if epoch is currently active, then it cannot be retired */
+        if (m_active) {
+            return false;
+        }
+
+        /* 
+         * if the epoch has active jobs but is not itself active, 
+         * wait for them to finish and return true. If there are 
+         * not active jobs, return true immediately 
+         */
+        while (m_active_jobs > 0) {
+            std::unique_lock<std::mutex> lk(m_cv_lock);
+            m_active_cv.wait(lk);
+        }
+
+        return true;
+    }
+
 private:
     Structure *m_structure;
     std::vector<Buffer *> m_buffers;
 
+    std::condition_variable m_active_cv;
+    std::mutex m_cv_lock;
+
     /*
      * The number of currently active jobs
      * (queries/merges) operating on this
@@ -126,5 +156,6 @@ private:
      * when this number is 0.
      */
     std::atomic<size_t> m_active_jobs;
+    bool m_active;
 };
 }