PPAPI: Make TrackedCallback more threadsafe

ppapi/shared_impl/callback_tracker.cc

Index: ppapi/shared_impl/callback_tracker.cc
diff --git a/ppapi/shared_impl/callback_tracker.cc b/ppapi/shared_impl/callback_tracker.cc
index feefb0e117d70aa862553838656da09763927824..e5154884a3159813b6d9bbff738dd2eab74e6fd3 100644
--- a/ppapi/shared_impl/callback_tracker.cc
+++ b/ppapi/shared_impl/callback_tracker.cc
@@ -11,6 +11,7 @@
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
 #include "ppapi/c/pp_completion_callback.h"
+#include "ppapi/shared_impl/proxy_lock.h"
 #include "ppapi/shared_impl/tracked_callback.h"
 
 namespace ppapi {
@@ -20,9 +21,17 @@ namespace ppapi {
 CallbackTracker::CallbackTracker() {}
 
 void CallbackTracker::AbortAll() {
-  // Iterate over a copy since |Abort()| calls |Remove()| (indirectly).
-  // TODO(viettrungluu): This obviously isn't so efficient.
-  CallbackSetMap pending_callbacks_copy = pending_callbacks_;
+  // TrackedCallback::Abort() assumes that the ProxyLock is acquired.
+  ProxyLock::AssertAcquired();
+
+  // Iterate over a copy:
+  // 1) because |Abort()| calls |Remove()| (indirectly).
+  // 2) So we can drop the lock before calling in to TrackedCallback.
+  CallbackSetMap pending_callbacks_copy;
+  {
+    base::AutoLock acquire(lock_);
+    pending_callbacks_copy = pending_callbacks_;
+  }
   for (CallbackSetMap::iterator it1 = pending_callbacks_copy.begin();
        it1 != pending_callbacks_copy.end();
        ++it1) {
@@ -36,15 +45,18 @@ void CallbackTracker::AbortAll() {
 
 void CallbackTracker::PostAbortForResource(PP_Resource resource_id) {
   CHECK(resource_id != 0);

[bbudge, 2015/02/25 23:51:31]

Why do we CHECK for 0 but fail silently for other invalid resource_id's?

[dmichael (off chromium), 2015/02/27 22:04:40]

0 is invalid and would imply a coding error in ResourceTracker when we call
this. The other cases are for when there was a valid resource that just had no
callbacks. I added some explanatory comments.

[bbudge, 2015/03/05 01:29:34]

OK

-  CallbackSetMap::iterator it1 = pending_callbacks_.find(resource_id);
-  if (it1 == pending_callbacks_.end())
-    return;
-  for (CallbackSet::iterator it2 = it1->second.begin();
-       it2 != it1->second.end();
-       ++it2) {
-    // Post the abort.
-    (*it2)->PostAbort();
+  CallbackSet callbacks_for_resource;
+  {
+    base::AutoLock acquire(lock_);
+    CallbackSetMap::iterator iter = pending_callbacks_.find(resource_id);
+    if (iter == pending_callbacks_.end())
+      return;
+    // Copy the set so we can drop the lock before calling in to
+    // TrackedCallback.
+    callbacks_for_resource = iter->second;
   }
+  for (const auto& iter : callbacks_for_resource)
+    iter->PostAbort();
 }
 
 CallbackTracker::~CallbackTracker() {
@@ -54,6 +66,7 @@ CallbackTracker::~CallbackTracker() {
 
 void CallbackTracker::Add(
     const scoped_refptr<TrackedCallback>& tracked_callback) {
+  base::AutoLock acquire(lock_);
   PP_Resource resource_id = tracked_callback->resource_id();
   DCHECK(pending_callbacks_[resource_id].find(tracked_callback) ==
          pending_callbacks_[resource_id].end());
@@ -62,6 +75,7 @@ void CallbackTracker::Add(
 
 void CallbackTracker::Remove(
     const scoped_refptr<TrackedCallback>& tracked_callback) {
+  base::AutoLock acquire(lock_);
   CallbackSetMap::iterator map_it =
       pending_callbacks_.find(tracked_callback->resource_id());
   DCHECK(map_it != pending_callbacks_.end());