detect blocking call in query handler (#227)

* detect blocking call in query handler

* fix lint

* use more descriptive error message

Author: yiminc

internal_worker.go

@@ -783,10 +783,7 @@ func (th *hostEnvImpl) decode(data []byte, to []interface{}) error {
 		}
 	}
 
-	if err := encoder.Unmarshal(data, to); err != nil {
-		return err
-	}
-	return nil
+	return encoder.Unmarshal(data, to)
 }
 
 // encode multiple arguments(arguments to a function).

internal_workflow.go

@@ -40,6 +40,8 @@ import (
 
 const (
 	defaultSignalChannelSize = 100000 // really large buffering size(100K)
+
+	panicIllegalAccessCoroutinueState = "getState: illegal access from outside of workflow context"
 )
 
 type (
@@ -461,7 +463,11 @@ func getState(ctx Context) *coroutineState {
 	if s == nil {
 		panic("getState: not workflow context")
 	}
-	return s.(*coroutineState)
+	state := s.(*coroutineState)
+	if !state.dispatcher.executing {
+		panic(panicIllegalAccessCoroutinueState)
+	}
+	return state
 }
 
 func (c *channelImpl) Receive(ctx Context, valuePtr interface{}) (more bool) {
@@ -1122,7 +1128,14 @@ func (h *queryHandler) execute(input []byte) (result []byte, err error) {
 	defer func() {
 		if p := recover(); p != nil {
 			result = nil
-			err = fmt.Errorf("handler for query type %s failed: %v", h.queryType, p)
+			st := getStackTraceRaw("query handler [panic]:", 7, 0)
+			if p == panicIllegalAccessCoroutinueState {
+				// query handler code try to access workflow functions outside of workflow context, make error message
+				// more descriptive and clear.
+				p = "query handler must not use cadence context to do things like cadence.NewChannel(), " +
+					"cadence.Go() or to call any workflow blocking functions like Channel.Get() or Future.Get()"
+			}
+			err = fmt.Errorf("query handler panic: %v, stack trace: %v", p, st)
 		}
 	}()
 

workflow.go

@@ -633,8 +633,10 @@ func GetVersion(ctx Context, changeID string, minSupported, maxSupported Version
 // All the input parameter must be serializable. You should call cadence.SetQueryHandler() at the beginning of the workflow
 // code. When client calls Client.QueryWorkflow() to cadence server, a task will be generated on server that will be dispatched
 // to a workflow worker, which will replay the history events and then execute a query handler based on the query type.
-// The query handler will be invoked out of the context of the workflow, meaning that the handler must not use cadence
-// context to call any workflow blocking functions like Channel.Get() or Future.Get().
+// The query handler will be invoked out of the context of the workflow, meaning that the handler code must not use cadence
+// context to do things like cadence.NewChannel(), cadence.Go() or to call any workflow blocking functions like
+// Channel.Get() or Future.Get(). Trying to do so in query handler code will fail the query and client will receive
+// QueryFailedError.
 // Example of workflow code that support query type "current_state":
 //  func MyWorkflow(ctx cadence.Context, input string) error {
 //    currentState := "started" // this could be any serializable struct