Fix a potential multi-thread issue when manipulating removable storage map

TBR=willchan@chromium.org
BUG=None

Review URL: https://chromiumcodereview.appspot.com/10905237

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@156486 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 21 insertions, 10 deletions

diff --git a/base/system_monitor/system_monitor.cc b/base/system_monitor/system_monitor.cc
index f30c893..2616275 100644
--- a/base/system_monitor/system_monitor.cc
+++ b/base/system_monitor/system_monitor.cc
@@ -103,27 +103,35 @@ void SystemMonitor::ProcessRemovableStorageAttached(
     const std::string& id,
     const string16& name,
     const FilePath::StringType& location) {
-  if (ContainsKey(removable_storage_map_, id)) {
-    // This can happen if our unique id scheme fails. Ignore the incoming
-    // non-unique attachment.
-    return;
+  {
+    base::AutoLock lock(removable_storage_lock_);
+    if (ContainsKey(removable_storage_map_, id)) {
+      // This can happen if our unique id scheme fails. Ignore the incoming
+      // non-unique attachment.
+      return;
+    }
+    RemovableStorageInfo info(id, name, location);
+    removable_storage_map_.insert(std::make_pair(id, info));
   }
-  RemovableStorageInfo info(id, name, location);
-  removable_storage_map_.insert(std::make_pair(id, info));
   NotifyRemovableStorageAttached(id, name, location);
 }
 
 void SystemMonitor::ProcessRemovableStorageDetached(const std::string& id) {
-  RemovableStorageMap::iterator it = removable_storage_map_.find(id);
-  if (it == removable_storage_map_.end())
-    return;
-  removable_storage_map_.erase(it);
+  {
+    base::AutoLock lock(removable_storage_lock_);
+    RemovableStorageMap::iterator it = removable_storage_map_.find(id);
+    if (it == removable_storage_map_.end())
+      return;
+    removable_storage_map_.erase(it);
+  }
   NotifyRemovableStorageDetached(id);
 }
 
 std::vector<SystemMonitor::RemovableStorageInfo>
 SystemMonitor::GetAttachedRemovableStorage() const {
   std::vector<RemovableStorageInfo> results;
+
+  base::AutoLock lock(removable_storage_lock_);
   for (RemovableStorageMap::const_iterator it = removable_storage_map_.begin();
        it != removable_storage_map_.end();
        ++it) {
diff --git a/base/system_monitor/system_monitor.h b/base/system_monitor/system_monitor.h
index 48d512b..f5224a4 100644
--- a/base/system_monitor/system_monitor.h
+++ b/base/system_monitor/system_monitor.h
@@ -13,6 +13,7 @@
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/string16.h"
+#include "base/synchronization/lock.h"
 #include "build/build_config.h"
 
 // Windows HiRes timers drain the battery faster so we need to know the battery
@@ -219,6 +220,8 @@ class BASE_EXPORT SystemMonitor {
   std::vector<id> notification_observers_;
 #endif
 
+  // For manipulating removable_storage_map_ structure.
+  mutable base::Lock removable_storage_lock_;
   // Map of all the attached removable storage devices.
   RemovableStorageMap removable_storage_map_;