Fix class unloading with the CC collector.
Avoid unnecessarily decoding dex cache and class loader weak roots,
which would trigger read barriers.
Re-enable 141-class-unload with the CC collector.
Bug: 12687968
Bug: 24468364
Change-Id: Ib4c19f25000873cab0e06047040442d135285745
diff --git a/runtime/java_vm_ext.cc b/runtime/java_vm_ext.cc
index b5e28e9..7cc05f7 100644
--- a/runtime/java_vm_ext.cc
+++ b/runtime/java_vm_ext.cc
@@ -56,15 +56,17 @@
class SharedLibrary {
public:
SharedLibrary(JNIEnv* env, Thread* self, const std::string& path, void* handle,
- jobject class_loader)
+ jobject class_loader, void* class_loader_allocator)
: path_(path),
handle_(handle),
needs_native_bridge_(false),
class_loader_(env->NewWeakGlobalRef(class_loader)),
+ class_loader_allocator_(class_loader_allocator),
jni_on_load_lock_("JNI_OnLoad lock"),
jni_on_load_cond_("JNI_OnLoad condition variable", jni_on_load_lock_),
jni_on_load_thread_id_(self->GetThreadId()),
jni_on_load_result_(kPending) {
+ CHECK(class_loader_allocator_ != nullptr);
}
~SharedLibrary() {
@@ -78,6 +80,10 @@
return class_loader_;
}
+ const void* GetClassLoaderAllocator() const {
+ return class_loader_allocator_;
+ }
+
const std::string& GetPath() const {
return path_;
}
@@ -169,6 +175,9 @@
// The ClassLoader this library is associated with, a weak global JNI reference that is
// created/deleted with the scope of the library.
const jweak class_loader_;
+ // Used to do equality check on class loaders so we can avoid decoding the weak root and read
+ // barriers that mess with class unloading.
+ const void* class_loader_allocator_;
// Guards remaining items.
Mutex jni_on_load_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
@@ -224,11 +233,15 @@
SHARED_REQUIRES(Locks::mutator_lock_) {
std::string jni_short_name(JniShortName(m));
std::string jni_long_name(JniLongName(m));
- const mirror::ClassLoader* declaring_class_loader = m->GetDeclaringClass()->GetClassLoader();
+ mirror::ClassLoader* const declaring_class_loader = m->GetDeclaringClass()->GetClassLoader();
ScopedObjectAccessUnchecked soa(Thread::Current());
+ void* const declaring_class_loader_allocator =
+ Runtime::Current()->GetClassLinker()->GetAllocatorForClassLoader(declaring_class_loader);
+ CHECK(declaring_class_loader_allocator != nullptr);
for (const auto& lib : libraries_) {
SharedLibrary* const library = lib.second;
- if (soa.Decode<mirror::ClassLoader*>(library->GetClassLoader()) != declaring_class_loader) {
+ // Use the allocator address for class loader equality to avoid unnecessary weak root decode.
+ if (library->GetClassLoaderAllocator() != declaring_class_loader_allocator) {
// We only search libraries loaded by the appropriate ClassLoader.
continue;
}
@@ -269,7 +282,7 @@
// If class_loader is a null jobject then it is the boot class loader. We should not unload
// the native libraries of the boot class loader.
if (class_loader != nullptr &&
- soa.Decode<mirror::ClassLoader*>(class_loader) == nullptr) {
+ soa.Self()->IsJWeakCleared(class_loader)) {
void* const sym = library->FindSymbol("JNI_OnUnload", nullptr);
if (sym == nullptr) {
VLOG(jni) << "[No JNI_OnUnload found in \"" << library->GetPath() << "\"]";
@@ -667,6 +680,19 @@
return weak_globals_.SynchronizedGet(ref);
}
+bool JavaVMExt::IsWeakGlobalCleared(Thread* self, IndirectRef ref) {
+ DCHECK_EQ(GetIndirectRefKind(ref), kWeakGlobal);
+ MutexLock mu(self, weak_globals_lock_);
+ while (UNLIKELY(!MayAccessWeakGlobals(self))) {
+ weak_globals_add_condition_.WaitHoldingLocks(self);
+ }
+ // When just checking a weak ref has been cleared, avoid triggering the read barrier in decode
+ // (DecodeWeakGlobal) so that we won't accidentally mark the object alive. Since the cleared
+ // sentinel is a non-moving object, we can compare the ref to it without the read barrier and
+ // decide if it's cleared.
+ return Runtime::Current()->IsClearedJniWeakGlobal(weak_globals_.Get<kWithoutReadBarrier>(ref));
+}
+
void JavaVMExt::UpdateWeakGlobal(Thread* self, IndirectRef ref, mirror::Object* result) {
MutexLock mu(self, weak_globals_lock_);
weak_globals_.Update(ref, result);
@@ -703,8 +729,19 @@
MutexLock mu(self, *Locks::jni_libraries_lock_);
library = libraries_->Get(path);
}
+ void* class_loader_allocator = nullptr;
+ {
+ ScopedObjectAccess soa(env);
+ // As the incoming class loader is reachable/alive during the call of this function,
+ // it's okay to decode it without worrying about unexpectedly marking it alive.
+ mirror::ClassLoader* loader = soa.Decode<mirror::ClassLoader*>(class_loader);
+ class_loader_allocator =
+ Runtime::Current()->GetClassLinker()->GetAllocatorForClassLoader(loader);
+ CHECK(class_loader_allocator != nullptr);
+ }
if (library != nullptr) {
- if (env->IsSameObject(library->GetClassLoader(), class_loader) == JNI_FALSE) {
+ // Use the allocator pointers for class loader equality to avoid unnecessary weak root decode.
+ if (library->GetClassLoaderAllocator() != class_loader_allocator) {
// The library will be associated with class_loader. The JNI
// spec says we can't load the same library into more than one
// class loader.
@@ -765,7 +802,7 @@
{
// Create SharedLibrary ahead of taking the libraries lock to maintain lock ordering.
std::unique_ptr<SharedLibrary> new_library(
- new SharedLibrary(env, self, path, handle, class_loader));
+ new SharedLibrary(env, self, path, handle, class_loader, class_loader_allocator));
MutexLock mu(self, *Locks::jni_libraries_lock_);
library = libraries_->Get(path);
if (library == nullptr) { // We won race to get libraries_lock.