Merge pull request hashicorp#233 from hashicorp/b-fix-alignment-on-32bit

Put 64bit atomics at the top of structs

observer.go

@@ -29,6 +29,12 @@ type FilterFn func(o *Observation) bool
 
 // Observer describes what to do with a given observation.
 type Observer struct {
+	// numObserved and numDropped are performance counters for this observer.
+	// 64 bit types must be 64 bit aligned to use with atomic operations on
+	// 32 bit platforms, so keep them at the top of the struct.
+	numObserved uint64
+	numDropped  uint64
+
 	// channel receives observations.
 	channel chan Observation
 
@@ -42,10 +48,6 @@ type Observer struct {
 
 	// id is the ID of this observer in the Raft map.
 	id uint64
-
-	// numObserved and numDropped are performance counters for this observer.
-	numObserved uint64
-	numDropped  uint64
 }
 
 // NewObserver creates a new observer that can be registered

state.go

@@ -42,6 +42,10 @@ func (s RaftState) String() string {
 // and provides an interface to set/get the variables in a
 // thread safe manner.
 type raftState struct {
+	// currentTerm commitIndex, lastApplied,  must be kept at the top of
+	// the struct so they're 64 bit aligned which is a requirement for
+	// atomic ops on 32 bit platforms.
+
 	// The current term, cache of StableStore
 	currentTerm uint64