fixes from review

mempool/mempool.go

@@ -100,6 +100,7 @@ func NewMempool(config *cfg.MempoolConfig, proxyAppConn proxy.AppConnMempool) *M
 
 // FireOnTxsAvailable initializes the TxsAvailable channel,
 // ensuring it will trigger once every height when transactions are available.
+// NOTE: not thread safe - should only be called once, on startup
 func (mem *Mempool) FireOnTxsAvailable() {
 	mem.txsAvailable = make(chan struct{}, 1)
 }
@@ -225,7 +226,7 @@ func (mem *Mempool) resCbNormal(req *abci.Request, res *abci.Response) {
 				tx:      req.GetCheckTx().Tx,
 			}
 			mem.txs.PushBack(memTx)
-			mem.alertIfTxsAvailable()
+			mem.notifyIfTxsAvailable()
 		} else {
 			// ignore bad transaction
 			mem.logger.Info("Bad Transaction", "res", r)
@@ -268,20 +269,13 @@ func (mem *Mempool) resCbRecheck(req *abci.Request, res *abci.Response) {
 			atomic.StoreInt32(&mem.rechecking, 0)
 			mem.logger.Info("Done rechecking txs")
 
-			mem.alertIfTxsAvailable()
+			mem.notifyIfTxsAvailable()
 		}
 	default:
 		// ignore other messages
 	}
 }
 
-func (mem *Mempool) alertIfTxsAvailable() {
-	if !mem.notifiedTxsAvailable && mem.Size() > 0 {
-		mem.notifiedTxsAvailable = true
-		mem.txsAvailable <- struct{}{}
-	}
-}
-
 // TxsAvailable returns a channel which fires once for every height,
 // and only when transactions are available in the mempool.
 // XXX: Will panic if mem.FireOnTxsAvailable() has not been called.
@@ -292,7 +286,7 @@ func (mem *Mempool) TxsAvailable() chan struct{} {
 	return mem.txsAvailable
 }
 
-func (mem *Mempool) alertIfTxsAvailable() {
+func (mem *Mempool) notifyIfTxsAvailable() {
 	if mem.txsAvailable != nil &&
 		!mem.notifiedTxsAvailable && mem.Size() > 0 {
 
@@ -345,6 +339,8 @@ func (mem *Mempool) Update(height int, txs types.Txs) {
 	}
 
 	// Set height
+	// NOTE: the height is not set until Update is first called
+	// (so it will be wrong after a restart until the next block)
 	mem.height = height
 	mem.notifiedTxsAvailable = false