fix(cancellation): handle message cancellation properly

a previous fix #391, attempted to address a lock that occurred on context cancel. however in doing
so, it introduced a new lock. essentially, if a message was not sent to the
requestmanager/responsemanager go routine, waiting for a response to that message could last
indefinitely. the previous fix therefore stopped waiting when the calling context cancelled. However
once a message reaches the go routine of the requestmanager/responsemanager, it's important that
it's processed to completion, so that the the message loop doesn't lock. The proper fix is to detect
when the message is sent successfully, and if so, wait for it to be processed. If it isn't sent, we
can safely abort the go routine immediately.

Author: hannahhoward

requestmanager/client.go

@@ -187,13 +187,14 @@ func (rm *RequestManager) NewRequest(ctx context.Context,
 
 	inProgressRequestChan := make(chan inProgressRequest)
 
-	rm.send(&newRequestMessage{requestID, span, p, root, selectorNode, extensions, inProgressRequestChan}, ctx.Done())
+	err := rm.send(&newRequestMessage{requestID, span, p, root, selectorNode, extensions, inProgressRequestChan}, ctx.Done())
+	if err != nil {
+		return rm.emptyResponse()
+	}
 	var receivedInProgressRequest inProgressRequest
 	select {
 	case <-rm.ctx.Done():
 		return rm.emptyResponse()
-	case <-ctx.Done():
-		return rm.emptyResponse()
 	case receivedInProgressRequest = <-inProgressRequestChan:
 	}
 
@@ -283,12 +284,13 @@ func (rm *RequestManager) cancelRequestAndClose(requestID graphsync.RequestID,
 // CancelRequest cancels the given request ID and waits for the request to terminate
 func (rm *RequestManager) CancelRequest(ctx context.Context, requestID graphsync.RequestID) error {
 	terminated := make(chan error, 1)
-	rm.send(&cancelRequestMessage{requestID, terminated, graphsync.RequestClientCancelledErr{}}, ctx.Done())
+	err := rm.send(&cancelRequestMessage{requestID, terminated, graphsync.RequestClientCancelledErr{}}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-terminated:
 		return err
 	}
@@ -300,19 +302,20 @@ func (rm *RequestManager) ProcessResponses(p peer.ID,
 	responses []gsmsg.GraphSyncResponse,
 	blks []blocks.Block) {
 
-	rm.send(&processResponsesMessage{p, responses, blks}, nil)
+	_ = rm.send(&processResponsesMessage{p, responses, blks}, nil)
 }
 
 // UnpauseRequest unpauses a request that was paused in a block hook based request ID
 // Can also send extensions with unpause
 func (rm *RequestManager) UnpauseRequest(ctx context.Context, requestID graphsync.RequestID, extensions ...graphsync.ExtensionData) error {
 	response := make(chan error, 1)
-	rm.send(&unpauseRequestMessage{requestID, extensions, response}, ctx.Done())
+	err := rm.send(&unpauseRequestMessage{requestID, extensions, response}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
@@ -321,12 +324,13 @@ func (rm *RequestManager) UnpauseRequest(ctx context.Context, requestID graphsyn
 // PauseRequest pauses an in progress request (may take 1 or more blocks to process)
 func (rm *RequestManager) PauseRequest(ctx context.Context, requestID graphsync.RequestID) error {
 	response := make(chan error, 1)
-	rm.send(&pauseRequestMessage{requestID, response}, ctx.Done())
+	err := rm.send(&pauseRequestMessage{requestID, response}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
@@ -335,26 +339,27 @@ func (rm *RequestManager) PauseRequest(ctx context.Context, requestID graphsync.
 // UpdateRequest updates an in progress request
 func (rm *RequestManager) UpdateRequest(ctx context.Context, requestID graphsync.RequestID, extensions ...graphsync.ExtensionData) error {
 	response := make(chan error, 1)
-	rm.send(&updateRequestMessage{requestID, extensions, response}, ctx.Done())
+	err := rm.send(&updateRequestMessage{requestID, extensions, response}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
 }
 
 // GetRequestTask gets data for the given task in the request queue
 func (rm *RequestManager) GetRequestTask(p peer.ID, task *peertask.Task, requestExecutionChan chan executor.RequestTask) {
-	rm.send(&getRequestTaskMessage{p, task, requestExecutionChan}, nil)
+	_ = rm.send(&getRequestTaskMessage{p, task, requestExecutionChan}, nil)
 }
 
 // ReleaseRequestTask releases a task request the requestQueue
 func (rm *RequestManager) ReleaseRequestTask(p peer.ID, task *peertask.Task, err error) {
 	done := make(chan struct{}, 1)
-	rm.send(&releaseRequestTaskMessage{p, task, err, done}, nil)
+	_ = rm.send(&releaseRequestTaskMessage{p, task, err, done}, nil)
 	select {
 	case <-rm.ctx.Done():
 	case <-done:
@@ -364,7 +369,7 @@ func (rm *RequestManager) ReleaseRequestTask(p peer.ID, task *peertask.Task, err
 // PeerState gets stats on all outgoing requests for a given peer
 func (rm *RequestManager) PeerState(p peer.ID) peerstate.PeerState {
 	response := make(chan peerstate.PeerState)
-	rm.send(&peerStateMessage{p, response}, nil)
+	_ = rm.send(&peerStateMessage{p, response}, nil)
 	select {
 	case <-rm.ctx.Done():
 		return peerstate.PeerState{}
@@ -392,11 +397,20 @@ func (rm *RequestManager) Shutdown() {
 	rm.cancel()
 }
 
-func (rm *RequestManager) send(message requestManagerMessage, done <-chan struct{}) {
+func (rm *RequestManager) send(message requestManagerMessage, done <-chan struct{}) error {
+	// prioritize cancelled context
+	select {
+	case <-done:
+		return errors.New("unable to send message before cancellation")
+	default:
+	}
 	select {
 	case <-rm.ctx.Done():
+		return rm.ctx.Err()
 	case <-done:
+		return errors.New("unable to send message before cancellation")
 	case rm.messages <- message:
+		return nil
 	}
 }
 

responsemanager/client.go

@@ -157,18 +157,19 @@ func New(ctx context.Context,
 
 // ProcessRequests processes incoming requests for the given peer
 func (rm *ResponseManager) ProcessRequests(ctx context.Context, p peer.ID, requests []gsmsg.GraphSyncRequest) {
-	rm.send(&processRequestsMessage{p, requests}, ctx.Done())
+	_ = rm.send(&processRequestsMessage{p, requests}, ctx.Done())
 }
 
 // UnpauseResponse unpauses a response that was previously paused
 func (rm *ResponseManager) UnpauseResponse(ctx context.Context, requestID graphsync.RequestID, extensions ...graphsync.ExtensionData) error {
 	response := make(chan error, 1)
-	rm.send(&unpauseRequestMessage{requestID, response, extensions}, ctx.Done())
+	err := rm.send(&unpauseRequestMessage{requestID, response, extensions}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
@@ -177,12 +178,13 @@ func (rm *ResponseManager) UnpauseResponse(ctx context.Context, requestID graphs
 // PauseResponse pauses an in progress response (may take 1 or more blocks to process)
 func (rm *ResponseManager) PauseResponse(ctx context.Context, requestID graphsync.RequestID) error {
 	response := make(chan error, 1)
-	rm.send(&pauseRequestMessage{requestID, response}, ctx.Done())
+	err := rm.send(&pauseRequestMessage{requestID, response}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
@@ -191,12 +193,13 @@ func (rm *ResponseManager) PauseResponse(ctx context.Context, requestID graphsyn
 // CancelResponse cancels an in progress response
 func (rm *ResponseManager) CancelResponse(ctx context.Context, requestID graphsync.RequestID) error {
 	response := make(chan error, 1)
-	rm.send(&errorRequestMessage{requestID, queryexecutor.ErrCancelledByCommand, response}, ctx.Done())
+	err := rm.send(&errorRequestMessage{requestID, queryexecutor.ErrCancelledByCommand, response}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
@@ -205,12 +208,13 @@ func (rm *ResponseManager) CancelResponse(ctx context.Context, requestID graphsy
 // UpdateRequest updates an in progress response
 func (rm *ResponseManager) UpdateResponse(ctx context.Context, requestID graphsync.RequestID, extensions ...graphsync.ExtensionData) error {
 	response := make(chan error, 1)
-	rm.send(&updateRequestMessage{requestID, extensions, response}, ctx.Done())
+	err := rm.send(&updateRequestMessage{requestID, extensions, response}, ctx.Done())
+	if err != nil {
+		return err
+	}
 	select {
 	case <-rm.ctx.Done():
 		return errors.New("context cancelled")
-	case <-ctx.Done():
-		return ctx.Err()
 	case err := <-response:
 		return err
 	}
@@ -219,7 +223,7 @@ func (rm *ResponseManager) UpdateResponse(ctx context.Context, requestID graphsy
 // Synchronize is a utility method that blocks until all current messages are processed
 func (rm *ResponseManager) synchronize() {
 	sync := make(chan error)
-	rm.send(&synchronizeMessage{sync}, nil)
+	_ = rm.send(&synchronizeMessage{sync}, nil)
 	select {
 	case <-rm.ctx.Done():
 	case <-sync:
@@ -228,18 +232,18 @@ func (rm *ResponseManager) synchronize() {
 
 // StartTask starts the given task from the peer task queue
 func (rm *ResponseManager) StartTask(task *peertask.Task, p peer.ID, responseTaskChan chan<- queryexecutor.ResponseTask) {
-	rm.send(&startTaskRequest{task, p, responseTaskChan}, nil)
+	_ = rm.send(&startTaskRequest{task, p, responseTaskChan}, nil)
 }
 
 // GetUpdates is called to read pending updates for a task and clear them
 func (rm *ResponseManager) GetUpdates(requestID graphsync.RequestID, updatesChan chan<- []gsmsg.GraphSyncRequest) {
-	rm.send(&responseUpdateRequest{requestID, updatesChan}, nil)
+	_ = rm.send(&responseUpdateRequest{requestID, updatesChan}, nil)
 }
 
 // FinishTask marks a task from the task queue as done
 func (rm *ResponseManager) FinishTask(task *peertask.Task, p peer.ID, err error) {
 	done := make(chan struct{}, 1)
-	rm.send(&finishTaskRequest{task, p, err, done}, nil)
+	_ = rm.send(&finishTaskRequest{task, p, err, done}, nil)
 	select {
 	case <-rm.ctx.Done():
 	case <-done:
@@ -249,7 +253,7 @@ func (rm *ResponseManager) FinishTask(task *peertask.Task, p peer.ID, err error)
 // CloseWithNetworkError closes a request due to a network error
 func (rm *ResponseManager) CloseWithNetworkError(requestID graphsync.RequestID) {
 	done := make(chan error, 1)
-	rm.send(&errorRequestMessage{requestID, queryexecutor.ErrNetworkError, done}, nil)
+	_ = rm.send(&errorRequestMessage{requestID, queryexecutor.ErrNetworkError, done}, nil)
 	select {
 	case <-rm.ctx.Done():
 	case <-done:
@@ -259,7 +263,7 @@ func (rm *ResponseManager) CloseWithNetworkError(requestID graphsync.RequestID)
 // TerminateRequest indicates a request has finished sending data and should no longer be tracked
 func (rm *ResponseManager) TerminateRequest(requestID graphsync.RequestID) {
 	done := make(chan struct{}, 1)
-	rm.send(&terminateRequestMessage{requestID, done}, nil)
+	_ = rm.send(&terminateRequestMessage{requestID, done}, nil)
 	select {
 	case <-rm.ctx.Done():
 	case <-done:
@@ -269,7 +273,7 @@ func (rm *ResponseManager) TerminateRequest(requestID graphsync.RequestID) {
 // PeerState gets current state of the outgoing responses for a given peer
 func (rm *ResponseManager) PeerState(p peer.ID) peerstate.PeerState {
 	response := make(chan peerstate.PeerState)
-	rm.send(&peerStateMessage{p, response}, nil)
+	_ = rm.send(&peerStateMessage{p, response}, nil)
 	select {
 	case <-rm.ctx.Done():
 		return peerstate.PeerState{}
@@ -278,11 +282,20 @@ func (rm *ResponseManager) PeerState(p peer.ID) peerstate.PeerState {
 	}
 }
 
-func (rm *ResponseManager) send(message responseManagerMessage, done <-chan struct{}) {
+func (rm *ResponseManager) send(message responseManagerMessage, done <-chan struct{}) error {
+	// prioritize cancelled context
+	select {
+	case <-done:
+		return errors.New("unable to send message before cancellation")
+	default:
+	}
 	select {
 	case <-rm.ctx.Done():
+		return rm.ctx.Err()
 	case <-done:
+		return errors.New("unable to send message before cancellation")
 	case rm.messages <- message:
+		return nil
 	}
 }