Fix locking on string init map (again).
Follow-up to
https://android-review.googlesource.com/172036 ,
https://android-review.googlesource.com/171621 .
Don't overwrite existing values, only insert new ones.
(Also improve performance by using move semantics.)
This prevents the following race: Thread 1 looks for string
init map for a method but doesn't find it, so it starts to
construct a new map. Thread 2 is doing the same but it's
faster and actually inserts the new map and keeps a pointer
to it. After Thread 2 releases the lock, Thread 1 acquires
it and starts to Overwrite() the element that the Thread 2
is currently using, so Thread 2 ends up looking at a map
that's being actively modified.
Change-Id: I135571af644363ea7bb282969a1bc7287b34f9b2
diff --git a/runtime/verifier/method_verifier.cc b/runtime/verifier/method_verifier.cc
index 3d4f04c..9938e90 100644
--- a/runtime/verifier/method_verifier.cc
+++ b/runtime/verifier/method_verifier.cc
@@ -548,7 +548,8 @@
MethodVerifier verifier(self, m->GetDexFile(), dex_cache, class_loader, &m->GetClassDef(),
m->GetCodeItem(), m->GetDexMethodIndex(), m, m->GetAccessFlags(),
true, true, false, true);
- return verifier.FindStringInitMap();
+ // Avoid copying: The map is moved out of the verifier before the verifier is destroyed.
+ return std::move(verifier.FindStringInitMap());
}
SafeMap<uint32_t, std::set<uint32_t>>& MethodVerifier::FindStringInitMap() {