Initial distributor implementation

appengine/cmd/dm/enums/execution/state.go

Index: appengine/cmd/dm/enums/execution/state.go
diff --git a/appengine/cmd/dm/enums/execution/state.go b/appengine/cmd/dm/enums/execution/state.go
index e4b00e66313a22185c7f37b6879128e3e440e3a7..be1564f677ff97ddcc4e9599e1272f33aca31d59 100644
--- a/appengine/cmd/dm/enums/execution/state.go
+++ b/appengine/cmd/dm/enums/execution/state.go
@@ -15,26 +15,76 @@ type State int8
 
 // State values
 const (
-	UnknownState State = iota
+	Unknown State = iota
 
+	// The execution has been accepted by the distributor, but is not running yet
 	Scheduled
-	Running
 
+	// The execution is running
+	Started
+
+	// The execution was unable to be accepted by the distributor
 	Rejected
+
+	// The execution was accepted by the distributor, but couldn't run in time.
+	TimedOut
+
+	// The execution ran and completed
 	Finished
-	Crashed
+
+	// The execution ran, but the distributor claims it did not complete
+	Failed
+
+	// The distributor claims to not know anything about this execution
+	Missing
+
+	// Some entity (DM, Human, Distributor) requested that this execution not run.
+	Cancelled
 )
 
 // validStateEvolution defines all valid {From -> []To} state transitions. The
 // identity transition (X -> X) is implied, as long as X has an entry in this
 // mapping.
 var validStateEvolution = map[State][]State{
-	Scheduled: {Running, Rejected, Crashed, Finished},
-	Running:   {Crashed, Finished, Rejected},
+	Scheduled: {Started, Finished, Missing, Cancelled, TimedOut},
+	Started:   {Finished, Failed, Missing, Cancelled},
+
+	Cancelled: {},
+	Finished:  {},
+	Failed:    {},
+	Missing:   {},
+	Rejected:  {},
+	TimedOut:  {},
+}
+
+// FromString returns the State for it's equivalent string representation.
+//
+// All unknown state vals are converted to Unknown.
+func FromString(val string) State {
+	switch val {
+	case "Scheduled":
+		return Scheduled
+	case "Started":
+		return Started
+	case "Rejected":
+		return Rejected
+	case "TimedOut":
+		return TimedOut
+	case "Finished":
+		return Finished
+	case "Failed":
+		return Failed
+	case "Missing":
+		return Missing
+	case "Cancelled":
+		return Cancelled
+	}
+	return Unknown
+}
 
-	Crashed:  {},
-	Finished: {},
-	Rejected: {},
+// IsTerminal returns True if State has no more valid evolutions.
+func (s State) IsTerminal() bool {
+	return len(validStateEvolution[s]) == 0
 }
 
 // Evolve attempts to evolve the state of this Attempt. If the state