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/*
* Copyright (C) 2015 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "lambda/box_table.h"
#include "base/mutex.h"
#include "common_throws.h"
#include "gc_root-inl.h"
#include "mirror/method.h"
#include "mirror/object-inl.h"
#include "thread.h"
#include <vector>
namespace art {
namespace lambda {
BoxTable::BoxTable()
: allow_new_weaks_(true),
new_weaks_condition_("lambda box table allowed weaks", *Locks::lambda_table_lock_) {}
mirror::Object* BoxTable::BoxLambda(const ClosureType& closure) {
Thread* self = Thread::Current();
{
// TODO: Switch to ReaderMutexLock if ConditionVariable ever supports RW Mutexes
/*Reader*/MutexLock mu(self, *Locks::lambda_table_lock_);
BlockUntilWeaksAllowed();
// Attempt to look up this object, it's possible it was already boxed previously.
// If this is the case we *must* return the same object as before to maintain
// referential equality.
//
// In managed code:
// Functional f = () -> 5; // vF = create-lambda
// Object a = f; // vA = box-lambda vA
// Object b = f; // vB = box-lambda vB
// assert(a == f)
ValueType value = FindBoxedLambda(closure);
if (!value.IsNull()) {
return value.Read();
}
// Otherwise we need to box ourselves and insert it into the hash map
}
// Release the lambda table lock here, so that thread suspension is allowed.
// Convert the ArtMethod into a java.lang.reflect.Method which will serve
// as the temporary 'boxed' version of the lambda. This is good enough
// to check all the basic object identities that a boxed lambda must retain.
// TODO: Boxing an innate lambda (i.e. made with create-lambda) should make a proxy class
// TODO: Boxing a learned lambda (i.e. made with unbox-lambda) should return the original object
mirror::Method* method_as_object =
mirror::Method::CreateFromArtMethod(self, closure);
// There are no thread suspension points after this, so we don't need to put it into a handle.
if (UNLIKELY(method_as_object == nullptr)) {
// Most likely an OOM has occurred.
CHECK(self->IsExceptionPending());
return nullptr;
}
// The method has been successfully boxed into an object, now insert it into the hash map.
{
MutexLock mu(self, *Locks::lambda_table_lock_);
BlockUntilWeaksAllowed();
// Lookup the object again, it's possible another thread already boxed it while
// we were allocating the object before.
ValueType value = FindBoxedLambda(closure);
if (UNLIKELY(!value.IsNull())) {
// Let the GC clean up method_as_object at a later time.
return value.Read();
}
// Otherwise we should insert it into the hash map in this thread.
map_.Insert(std::make_pair(closure, ValueType(method_as_object)));
}
return method_as_object;
}
bool BoxTable::UnboxLambda(mirror::Object* object, ClosureType* out_closure) {
DCHECK(object != nullptr);
*out_closure = nullptr;
// Note that we do not need to access lambda_table_lock_ here
// since we don't need to look at the map.
mirror::Object* boxed_closure_object = object;
// Raise ClassCastException if object is not instanceof java.lang.reflect.Method
if (UNLIKELY(!boxed_closure_object->InstanceOf(mirror::Method::StaticClass()))) {
ThrowClassCastException(mirror::Method::StaticClass(), boxed_closure_object->GetClass());
return false;
}
// TODO(iam): We must check that the closure object extends/implements the type
// specified in [type id]. This is not currently implemented since it's always a Method.
// If we got this far, the inputs are valid.
// Write out the java.lang.reflect.Method's embedded ArtMethod* into the vreg target.
mirror::AbstractMethod* boxed_closure_as_method =
down_cast<mirror::AbstractMethod*>(boxed_closure_object);
ArtMethod* unboxed_closure = boxed_closure_as_method->GetArtMethod();
DCHECK(unboxed_closure != nullptr);
*out_closure = unboxed_closure;
return true;
}
BoxTable::ValueType BoxTable::FindBoxedLambda(const ClosureType& closure) const {
auto map_iterator = map_.Find(closure);
if (map_iterator != map_.end()) {
const std::pair<ClosureType, ValueType>& key_value_pair = *map_iterator;
const ValueType& value = key_value_pair.second;
DCHECK(!value.IsNull()); // Never store null boxes.
return value;
}
return ValueType(nullptr);
}
void BoxTable::BlockUntilWeaksAllowed() {
Thread* self = Thread::Current();
while (UNLIKELY(allow_new_weaks_ == false)) {
new_weaks_condition_.WaitHoldingLocks(self); // wait while holding mutator lock
}
}
void BoxTable::SweepWeakBoxedLambdas(IsMarkedVisitor* visitor) {
DCHECK(visitor != nullptr);
Thread* self = Thread::Current();
MutexLock mu(self, *Locks::lambda_table_lock_);
/*
* Visit every weak root in our lambda box table.
* Remove unmarked objects, update marked objects to new address.
*/
std::vector<ClosureType> remove_list;
for (auto map_iterator = map_.begin(); map_iterator != map_.end(); ) {
std::pair<ClosureType, ValueType>& key_value_pair = *map_iterator;
const ValueType& old_value = key_value_pair.second;
// This does not need a read barrier because this is called by GC.
mirror::Object* old_value_raw = old_value.Read<kWithoutReadBarrier>();
mirror::Object* new_value = visitor->IsMarked(old_value_raw);
if (new_value == nullptr) {
const ClosureType& closure = key_value_pair.first;
// The object has been swept away.
// Delete the entry from the map.
map_iterator = map_.Erase(map_.Find(closure));
} else {
// The object has been moved.
// Update the map.
key_value_pair.second = ValueType(new_value);
++map_iterator;
}
}
// Occasionally shrink the map to avoid growing very large.
if (map_.CalculateLoadFactor() < kMinimumLoadFactor) {
map_.ShrinkToMaximumLoad();
}
}
void BoxTable::DisallowNewWeakBoxedLambdas() {
Thread* self = Thread::Current();
MutexLock mu(self, *Locks::lambda_table_lock_);
allow_new_weaks_ = false;
}
void BoxTable::AllowNewWeakBoxedLambdas() {
Thread* self = Thread::Current();
MutexLock mu(self, *Locks::lambda_table_lock_);
allow_new_weaks_ = true;
new_weaks_condition_.Broadcast(self);
}
void BoxTable::EnsureNewWeakBoxedLambdasDisallowed() {
Thread* self = Thread::Current();
MutexLock mu(self, *Locks::lambda_table_lock_);
CHECK_NE(allow_new_weaks_, false);
}
bool BoxTable::EqualsFn::operator()(const ClosureType& lhs, const ClosureType& rhs) const {
// Nothing needs this right now, but leave this assertion for later when
// we need to look at the references inside of the closure.
if (kIsDebugBuild) {
Locks::mutator_lock_->AssertSharedHeld(Thread::Current());
}
// TODO: Need rework to use read barriers once closures have references inside of them that can
// move. Until then, it's safe to just compare the data inside of it directly.
return lhs == rhs;
}
} // namespace lambda
} // namespace art