issue #934: multithread compactiong support

Author: caijieming

src/leveldb/db/db_impl.cc

@@ -114,7 +114,7 @@ class DBImpl : public DB {
   Status CompactMemTable()
       EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
-  Status WriteLevel0Table(MemTable* mem, VersionEdit* edit, Version* base)
+  Status WriteLevel0Table(MemTable* mem, VersionEdit* edit, Version* base, uint64_t* number = NULL)
       EXCLUSIVE_LOCKS_REQUIRED(mutex_);
 
   Status MakeRoomForWrite(bool force /* compact even if there is room? */)
@@ -193,17 +193,24 @@ class DBImpl : public DB {
   std::set<uint64_t> pending_outputs_;
 
   // Has a background compaction been scheduled or is running?
-  bool bg_compaction_scheduled_;
-  double bg_compaction_score_;
-  int64_t bg_schedule_id_;
+  int bg_compaction_scheduled_;
+  std::vector<double> bg_compaction_score_;
+  std::vector<int64_t> bg_schedule_id_;
 
   // Information for a manual compaction
+  enum ManualCompactState {
+    kManualCompactIdle,
+    kManualCompactConflict,
+    kManualCompactWakeup,
+  };
   struct ManualCompaction {
     int level;
     bool done;
+    bool being_sched;
     const InternalKey* begin;   // NULL means beginning of key range
     const InternalKey* end;     // NULL means end of key range
     InternalKey tmp_storage;    // Used to keep track of compaction progress
+    int compaction_conflict; // 0 == idle, 1 == conflict, 2 == wake
   };
   ManualCompaction* manual_compaction_;