Removed DBImpl::notifying_events_

Summary:
DBImpl::notifying_events_ is a internal counter in DBImpl which is
used to prevent DB close when DB is notifying events.  However, as
the current events all rely on either compaction or flush which
already have similar counters to prevent DB close, it is safe to
remove notifying_events_.

Test Plan:
listener_test
examples/compact_files_example

Reviewers: igor, anthony, kradhakrishnan, rven, sdong

Reviewed By: sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D39315

db/db_impl.cc

@@ -245,8 +245,7 @@ DBImpl::DBImpl(const DBOptions& options, const std::string& dbname)
       event_logger_(db_options_.info_log.get()),
       bg_work_gate_closed_(false),
       refitting_level_(false),
-      opened_successfully_(false),
-      notifying_events_(0) {
+      opened_successfully_(false) {
   env_->GetAbsolutePath(dbname, &db_absolute_path_);
 
   // Reserve ten files or so for other uses and give the rest to TableCache.
@@ -279,7 +278,7 @@ void DBImpl::CancelAllBackgroundWork(bool wait) {
   }
   // Wait for background work to finish
   mutex_.Lock();
-  while (bg_compaction_scheduled_ || bg_flush_scheduled_ || notifying_events_) {
+  while (bg_compaction_scheduled_ || bg_flush_scheduled_) {
     bg_cv_.Wait();
   }
   mutex_.Unlock();
@@ -314,7 +313,7 @@ DBImpl::~DBImpl() {
   bg_flush_scheduled_ -= flushes_unscheduled;
 
   // Wait for background work to finish
-  while (bg_compaction_scheduled_ || bg_flush_scheduled_ || notifying_events_) {
+  while (bg_compaction_scheduled_ || bg_flush_scheduled_) {
     bg_cv_.Wait();
   }
   flush_scheduler_.Clear();
@@ -1279,7 +1278,6 @@ void DBImpl::NotifyOnFlushCompleted(
   bool triggered_flush_stop =
       (cfd->current()->storage_info()->NumLevelFiles(0) >=
        mutable_cf_options.level0_stop_writes_trigger);
-  notifying_events_++;
   // release lock while notifying events
   mutex_.Unlock();
   {
@@ -1294,8 +1292,6 @@ void DBImpl::NotifyOnFlushCompleted(
     }
   }
   mutex_.Lock();
-  notifying_events_--;
-  assert(notifying_events_ >= 0);
   // no need to signal bg_cv_ as it will be signaled at the end of the
   // flush process.
 #endif  // ROCKSDB_LITE
@@ -1549,6 +1545,9 @@ Status DBImpl::CompactFilesImpl(
   }
 
   bg_compaction_scheduled_--;
+  if (bg_compaction_scheduled_ == 0) {
+    bg_cv_.SignalAll();
+  }
 
   return status;
 }
@@ -1564,7 +1563,6 @@ void DBImpl::NotifyOnCompactionCompleted(
   if (shutting_down_.load(std::memory_order_acquire)) {
     return;
   }
-  notifying_events_++;
   // release lock while notifying events
   mutex_.Unlock();
   {
@@ -1591,8 +1589,6 @@ void DBImpl::NotifyOnCompactionCompleted(
     }
   }
   mutex_.Lock();
-  notifying_events_--;
-  assert(notifying_events_ >= 0);
   // no need to signal bg_cv_ as it will be signaled at the end of the
   // flush process.
 #endif  // ROCKSDB_LITE

db/db_impl.h

@@ -688,9 +688,6 @@ class DBImpl : public DB {
   // Indicate DB was opened successfully
   bool opened_successfully_;
 
-  // count how many events are currently being notified.
-  int notifying_events_;
-
   // No copying allowed
   DBImpl(const DBImpl&);
   void operator=(const DBImpl&);