use CAS for compacting state

chain/store/splitstore/splitstore.go

@@ -5,6 +5,7 @@ import (
 	"encoding/binary"
 	"errors"
 	"sync"
+	"sync/atomic"
 	"time"
 
 	"github.com/bmatsuo/lmdb-go/lmdb"
@@ -28,10 +29,12 @@ var baseEpochKey = dstore.NewKey("baseEpoch")
 var log = logging.Logger("splitstore")
 
 type SplitStore struct {
-	mx         sync.Mutex
-	baseEpoch  abi.ChainEpoch
-	curTs      *types.TipSet
-	compacting bool
+	compacting int32
+
+	baseEpoch abi.ChainEpoch
+
+	mx    sync.Mutex
+	curTs *types.TipSet
 
 	cs *store.ChainStore
 	ds dstore.Datastore
@@ -204,9 +207,9 @@ func (s *SplitStore) Start(cs *store.ChainStore) error {
 }
 
 func (s *SplitStore) Close() error {
-	if s.isCompacting() {
+	if atomic.LoadInt32(&s.compacting) == 1 {
 		log.Warn("ongoing compaction; waiting for it to finish...")
-		for s.isCompacting() {
+		for atomic.LoadInt32(&s.compacting) == 1 {
 			time.Sleep(time.Second)
 		}
 	}
@@ -220,10 +223,14 @@ func (s *SplitStore) HeadChange(revert, apply []*types.TipSet) error {
 	epoch := s.curTs.Height()
 	s.mx.Unlock()
 
-	if !s.isCompacting() && epoch-s.baseEpoch > CompactionThreshold {
-		s.setCompacting(true)
+	if !atomic.CompareAndSwapInt32(&s.compacting, 0, 1) {
+		// we are currently compacting, do nothing and wait for the next head change
+		return nil
+	}
+
+	if epoch-s.baseEpoch > CompactionThreshold {
 		go func() {
-			defer s.setCompacting(false)
+			defer atomic.StoreInt32(&s.compacting, 0)
 
 			log.Info("compacting splitstore")
 			start := time.Now()
@@ -232,23 +239,14 @@ func (s *SplitStore) HeadChange(revert, apply []*types.TipSet) error {
 
 			log.Infow("compaction done", "took", time.Since(start))
 		}()
+	} else {
+		// no compaction necessary
+		atomic.StoreInt32(&s.compacting, 0)
 	}
 
 	return nil
 }
 
-func (s *SplitStore) isCompacting() bool {
-	s.mx.Lock()
-	defer s.mx.Unlock()
-	return s.compacting
-}
-
-func (s *SplitStore) setCompacting(state bool) {
-	s.mx.Lock()
-	defer s.mx.Unlock()
-	s.compacting = state
-}
-
 // Compaction/GC Algorithm
 func (s *SplitStore) compact() {
 	// create two on disk live sets, one for marking the cold finality region