initial implementation, might not compile

Author: matthewvon

db/db_impl/db_impl_compaction_flush.cc

@@ -1704,13 +1704,15 @@ Status DBImpl::Flush(const FlushOptions& flush_options,
   ROCKS_LOG_INFO(immutable_db_options_.info_log, "[%s] Manual flush start.",
                  cfh->GetName().c_str());
   Status s;
+  cfh->imm.BeginManualOperation();
   if (immutable_db_options_.atomic_flush) {
     s = AtomicFlushMemTables({cfh->cfd()}, flush_options,
                              FlushReason::kManualFlush);
   } else {
     s = FlushMemTable(cfh->cfd(), flush_options, FlushReason::kManualFlush);
   }
 
+  cfh->imm.CompleteManualOperation();
   ROCKS_LOG_INFO(immutable_db_options_.info_log,
                  "[%s] Manual flush finished, status: %s\n",
                  cfh->GetName().c_str(), s.ToString().c_str());

db/memtable_list.cc

@@ -329,7 +329,8 @@ bool MemTableListVersion::TrimHistory(autovector<MemTable*>* to_delete,
 // not yet started.
 bool MemTableList::IsFlushPending() const {
   if ((flush_requested_ && num_flush_not_started_ > 0) ||
-      (num_flush_not_started_ >= min_write_buffer_number_to_merge_)) {
+      (num_flush_not_started_ >= min_write_buffer_number_to_merge_) ||
+      (active_manuals_ && num_flush_not_started_)) {
     assert(imm_flush_needed.load(std::memory_order_relaxed));
     return true;
   }

db/memtable_list.h

@@ -391,6 +391,12 @@ class MemTableList {
   void RemoveOldMemTables(uint64_t log_number,
                           autovector<MemTable*>* to_delete);
 
+  void BeginManualOperation() {++active_manuals_};
+
+  void CompleteManualOperation() {
+    assert(active_manuals >= 1);
+    --active_manuals_};
+
  private:
   friend Status InstallMemtableAtomicFlushResults(
       const autovector<MemTableList*>* imm_lists,
@@ -436,6 +442,9 @@ class MemTableList {
 
   // Cached value of current_->HasHistory().
   std::atomic<bool> current_has_history_;
+
+  // count of manual flush/compactions active
+  std::atomic<int> active_manuals_{0};
 };
 
 // Installs memtable atomic flush results.