From 6cb6d9cdf1e0303d1c8a06dbbb650752d2868fdb Mon Sep 17 00:00:00 2001
From: Michael Schurter <schmichael@hashicorp.com>
Date: Fri, 2 Sep 2016 15:39:22 -0700
Subject: [PATCH] Lock around saving state

Prevent interleaving state syncs as it could conceivably lead to
empty state files as per #1367
---
 client/alloc_runner.go | 7 +++++++
 client/task_runner.go  | 6 ++++++
 2 files changed, 13 insertions(+)

diff --git a/client/alloc_runner.go b/client/alloc_runner.go
index d79374ef1..ee7ab9c06 100644
--- a/client/alloc_runner.go
+++ b/client/alloc_runner.go
@@ -66,6 +66,9 @@ type AllocRunner struct {
 	destroyCh   chan struct{}
 	destroyLock sync.Mutex
 	waitCh      chan struct{}
+
+	// serialize saveAllocRunnerState calls
+	persistLock sync.Mutex
 }
 
 // allocRunnerState is used to snapshot the state of the alloc runner
@@ -179,8 +182,12 @@ func (r *AllocRunner) SaveState() error {
 }
 
 func (r *AllocRunner) saveAllocRunnerState() error {
+	r.persistLock.Lock()
+	defer r.persistLock.Unlock()
+
 	// Create the snapshot.
 	alloc := r.Alloc()
+
 	r.allocLock.Lock()
 	states := alloc.TaskStates
 	allocClientStatus := r.allocClientStatus
diff --git a/client/task_runner.go b/client/task_runner.go
index 208f2ab25..b68fbeb65 100644
--- a/client/task_runner.go
+++ b/client/task_runner.go
@@ -69,6 +69,9 @@ type TaskRunner struct {
 	destroyLock  sync.Mutex
 	destroyEvent *structs.TaskEvent
 	waitCh       chan struct{}
+
+	// serialize SaveState calls
+	persistLock sync.Mutex
 }
 
 // taskRunnerState is used to snapshot the state of the task runner
@@ -186,6 +189,9 @@ func (r *TaskRunner) RestoreState() error {
 
 // SaveState is used to snapshot our state
 func (r *TaskRunner) SaveState() error {
+	r.persistLock.Lock()
+	defer r.persistLock.Unlock()
+
 	snap := taskRunnerState{
 		Task:               r.task,
 		Version:            r.config.Version,