reorganize bisect function so we lock it properly

db/db_resolve.go

@@ -37,11 +37,7 @@ func PrepareResolveResult(
 		return nil, err
 	}
 
-	var txCounts []interface{}
+	height, createdHeight := db.TxCounts.TxCountsBisectRight(txNum, rootTxNum, BisectRight)
-	txCounts = db.TxCounts.GetSlice()
-	txCounts = txCounts[:db.TxCounts.Len()]
-	height := BisectRight(txCounts, txNum)
-	createdHeight := BisectRight(txCounts, rootTxNum)
 	lastTakeoverHeight := controllingClaim.Height
 
 	expirationHeight := GetExpirationHeight(height)

db/db_stack/db_stack.go

@@ -1,6 +1,8 @@
 package db_stack
 
-import "sync"
+import (
+	"sync"
+)
 
 type SliceBackedStack struct {
 	slice []interface{}
@@ -77,3 +79,18 @@ func (s *SliceBackedStack) GetSlice() []interface{} {
 	// This is not thread safe so I won't bother with locking
 	return s.slice
 }
+
+// This function is dangerous because it assumes underlying types
+func (s *SliceBackedStack) TxCountsBisectRight(
+	txNum, rootTxNum uint32,
+	bisectFunc func([]interface{}, uint32) uint32,
+) (uint32, uint32) {
+	s.mut.RLock()
+	defer s.mut.RUnlock()
+
+	txCounts := s.slice[:s.Len()]
+	height := bisectFunc(txCounts, txNum)
+	createdHeight := bisectFunc(txCounts, rootTxNum)
+
+	return height, createdHeight
+}