Merge pull request btcsuite#2273 from ynewmann/fix/batch-data-race

rpcclient: safe read and write to batch

rpcclient/infrastructure.go

@@ -74,6 +74,9 @@ var (
 	// client having already connected to the RPC server.
 	ErrClientAlreadyConnected = errors.New("websocket client has already " +
 		"connected")
+
+	// ErrEmptyBatch is an error to describe that there is nothing to send.
+	ErrEmptyBatch = errors.New("batch is empty")
 )
 
 const (
@@ -151,6 +154,7 @@ type Client struct {
 
 	// whether or not to batch requests, false unless changed by Batch()
 	batch     bool
+	batchLock sync.Mutex
 	batchList *list.List
 
 	// retryCount holds the number of times the client has tried to
@@ -214,7 +218,10 @@ func (c *Client) addRequest(jReq *jsonRequest) error {
 		element := c.requestList.PushBack(jReq)
 		c.requestMap[jReq.id] = element
 	} else {
+		c.batchLock.Lock()
 		element := c.batchList.PushBack(jReq)
+		c.batchLock.Unlock()
+
 		c.requestMap[jReq.id] = element
 	}
 	return nil
@@ -238,7 +245,9 @@ func (c *Client) removeRequest(id uint64) *jsonRequest {
 
 	var request *jsonRequest
 	if c.batch {
+		c.batchLock.Lock()
 		request = c.batchList.Remove(element).(*jsonRequest)
+		c.batchLock.Unlock()
 	} else {
 		request = c.requestList.Remove(element).(*jsonRequest)
 	}
@@ -1672,7 +1681,15 @@ func (c *Client) BackendVersion() (BackendVersion, error) {
 	return c.backendVersion, nil
 }
 
-func (c *Client) sendAsync() FutureGetBulkResult {
+func (c *Client) sendAsync() (FutureGetBulkResult, error) {
+	c.batchLock.Lock()
+	defer c.batchLock.Unlock()
+
+	// If batchList is empty, there's nothing to send.
+	if c.batchList.Len() == 0 {
+		return nil, ErrEmptyBatch
+	}
+
 	// convert the array of marshalled json requests to a single request we can send
 	responseChan := make(chan *Response, 1)
 	marshalledRequest := []byte("[")
@@ -1694,25 +1711,24 @@ func (c *Client) sendAsync() FutureGetBulkResult {
 		responseChan:   responseChan,
 	}
 	c.sendPostRequest(&request)
-	return responseChan
+	return responseChan, nil
 }
 
 // Marshall's bulk requests and sends to the server
 // creates a response channel to receive the response
 func (c *Client) Send() error {
-	// if batchlist is empty, there's nothing to send
-	if c.batchList.Len() == 0 {
-		return nil
+	future, err := c.sendAsync()
+	if err != nil {
+		return err
 	}
 
-	batchResp, err := c.sendAsync().Receive()
+	batchResp, err := future.Receive()
 	if err != nil {
 		// Clear batchlist in case of an error.
-		//
-		// TODO(yy): need to double check to make sure there's no
-		// concurrent access to this batch list, otherwise we may miss
-		// some batched requests.
+
+		c.batchLock.Lock()
 		c.batchList = list.New()
+		c.batchLock.Unlock()
 
 		return err
 	}
@@ -1722,6 +1738,10 @@ func (c *Client) Send() error {
 		// Perform a GC on batchList and requestMap before moving
 		// forward.
 		request := c.removeRequest(id)
+		if request == nil {
+			// Perhaps another goroutine has already processed this request.
+			continue
+		}
 
 		// If there's an error, we log it and continue to the next
 		// request.