PPAPI: Fix GetBrowserInterface race conditions

ppapi/proxy/interface_list.h

Index: ppapi/proxy/interface_list.h
diff --git a/ppapi/proxy/interface_list.h b/ppapi/proxy/interface_list.h
index a2b4569c8f1b3b3693af6f85b068e82095a334c4..16c6c4d18b1558b4c9e62335ca44085b13a99b06 100644
--- a/ppapi/proxy/interface_list.h
+++ b/ppapi/proxy/interface_list.h
@@ -8,7 +8,9 @@
 #include <map>
 #include <string>
 
+#include "base/atomic_sequence_num.h"
 #include "base/basictypes.h"
+#include "base/containers/scoped_ptr_hash_map.h"
 #include "ppapi/proxy/interface_proxy.h"
 #include "ppapi/proxy/ppapi_proxy_export.h"
 #include "ppapi/shared_impl/ppapi_permissions.h"
@@ -50,13 +52,11 @@ class PPAPI_PROXY_EXPORT InterfaceList {
   struct InterfaceInfo {
     InterfaceInfo()
         : iface(NULL),
-          required_permission(PERMISSION_NONE),
-          interface_logged(false) {
+          required_permission(PERMISSION_NONE) {
     }
     InterfaceInfo(const void* in_interface, Permission in_perm)
         : iface(in_interface),
-          required_permission(in_perm),
-          interface_logged(false) {
+          required_permission(in_perm) {
     }
 
     const void* iface;
@@ -66,11 +66,16 @@ class PPAPI_PROXY_EXPORT InterfaceList {
     // an interface is requested.
     Permission required_permission;
 
-    // Interface usage is logged just once per-interface-per-plugin-process.
-    bool interface_logged;
+    // Count how many times the interface has been requested. This helps us
+    // only log the first time the interface is requested (or in the unlikely
+    // event that the count rolls over).
+    base::AtomicSequenceNumber interface_request_count_;

[teravest, 2014/09/12 19:08:27]

Since we don't really need a sequence number, I wonder if it'd be better to use
either:
  CompareAndSwap, or
  an internal lock that's only held (briefly) when managing a flag.

Since this shouldn't be contended, now that I think about it, it seems like a
mutex+flag should be fine.

[dmichael (off chromium), 2014/09/12 20:44:00]

done with a lock-per-interface. Contention should be incredibly rare.

+   private:
+    DISALLOW_COPY_AND_ASSIGN(InterfaceInfo);
   };
 
-  typedef std::map<std::string, InterfaceInfo> NameToInterfaceInfoMap;
+  typedef base::ScopedPtrHashMap<std::string, InterfaceInfo>
+      NameToInterfaceInfoMap;

[dmichael (off chromium), 2014/09/12 18:12:07]

changed because AtomicSequenceNumber is not copyable

 
   void AddProxy(ApiID id, InterfaceProxy::Factory factory);