Fix HandleMaxWalSize ScheduleFlush conflict (#140)

Author: mm304321141

db/db_impl_write.cc

@@ -1241,7 +1241,7 @@ Status DBImpl::HandleMaxWalSize(WriteContext* write_context) {
       }
     }
   }
-  if (cfd_picked != nullptr) {
+  if (cfd_picked != nullptr && cfd_picked->mem()->SwitchFlushScheduled()) {
     uint64_t alive_log_files_back_size = alive_log_files_.back().size;
     uint64_t max_wal_size = GetMaxWalSize();
     ROCKS_LOG_BUFFER(

db/memtable.h

@@ -149,6 +149,16 @@ class MemTable {
                                                 std::memory_order_relaxed);
   }
 
+  bool SwitchFlushScheduled() {
+    auto state = flush_state_.load(std::memory_order_relaxed);
+    if (state == FLUSH_NOT_REQUESTED) {
+      flush_state_.compare_exchange_strong(state, FLUSH_REQUESTED,
+                                           std::memory_order_relaxed,
+                                           std::memory_order_relaxed);
+    }
+    return MarkFlushScheduled();
+  }
+
   // Return an iterator that yields the contents of the memtable.
   //
   // The caller must ensure that the underlying MemTable remains live