Initial distributor implementation

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

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 //go:generate stringer -type=State
 
 package attempt
 
 import (
         "fmt"
 )
 
 // State is the enumeration of possible states for an Attempt.
 type State int8
 
 // These are the only valid enumerated values for State.
 const (
         UnknownState State = iota
         NeedsExecution
         Executing
         AddingDeps
         Blocked
+        AwaitingExecutionState
         Finished
 )
 
 // 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{
-        AddingDeps:     {Blocked, NeedsExecution},
-        Blocked:        {NeedsExecution},
-        Executing:      {AddingDeps, Finished},
-        Finished:       {},
-        NeedsExecution: {Executing},
+        AddingDeps:             {Blocked, NeedsExecution},
+        Blocked:                {AwaitingExecutionState, NeedsExecution},
+        AwaitingExecutionState: {NeedsExecution},
+        Executing:              {AddingDeps, Finished},
+        Finished:               {},
+        NeedsExecution:         {Executing},
 }
 
 // Evolve attempts to evolve the state of this Attempt. If the state
 // evolution is not allowed (e.g. invalid state transition), this returns an
 // error.
 func (s *State) Evolve(newState State) error {
         nextStates := validStateEvolution[*s]
         if nextStates == nil {
                 return fmt.Errorf("invalid state transition: no transitions defined for %s", *s)
         }
@@ skipping 12 matching lines @@
         return fmt.Errorf("invalid state transition %v -> %v", *s, newState)
 }
 
 // MustEvolve is a panic'ing version of Evolve.
 func (s *State) MustEvolve(newState State) {
         err := s.Evolve(newState)
         if err != nil {
                 panic(err)
         }
 }