runtime/scoped_thread_state_change.h - platform/art - Gitiles

 /*
  * Copyright (C) 2012 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.
  */

 #ifndef ART_RUNTIME_SCOPED_THREAD_STATE_CHANGE_H_
 #define ART_RUNTIME_SCOPED_THREAD_STATE_CHANGE_H_

 #include "base/casts.h"
 #include "java_vm_ext.h"
 #include "jni_env_ext-inl.h"
 #include "mirror/art_field.h"
 #include "read_barrier.h"
 #include "thread-inl.h"
 #include "verify_object.h"

 namespace art {

 // Scoped change into and out of a particular state. Handles Runnable transitions that require
 // more complicated suspension checking. The subclasses ScopedObjectAccessUnchecked and
 // ScopedObjectAccess are used to handle the change into Runnable to Get direct access to objects,
 // the unchecked variant doesn't aid annotalysis.
 class ScopedThreadStateChange {
  public:
   ScopedThreadStateChange(Thread* self, ThreadState new_thread_state)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
       : self_(self), thread_state_(new_thread_state), expected_has_no_thread_(false) {
     if (UNLIKELY(self_ == NULL)) {
       // Value chosen arbitrarily and won't be used in the destructor since thread_ == NULL.
       old_thread_state_ = kTerminated;
       Runtime* runtime = Runtime::Current();
       CHECK(runtime == NULL || !runtime->IsStarted() || runtime->IsShuttingDown(self_));
     } else {
       DCHECK_EQ(self, Thread::Current());
       // Read state without locks, ok as state is effectively thread local and we're not interested
       // in the suspend count (this will be handled in the runnable transitions).
       old_thread_state_ = self->GetState();
       if (old_thread_state_ != new_thread_state) {
         if (new_thread_state == kRunnable) {
           self_->TransitionFromSuspendedToRunnable();
         } else if (old_thread_state_ == kRunnable) {
           self_->TransitionFromRunnableToSuspended(new_thread_state);
         } else {
           // A suspended transition to another effectively suspended transition, ok to use Unsafe.
           self_->SetState(new_thread_state);
         }
       }
     }
   }

   ~ScopedThreadStateChange() LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE {
     if (UNLIKELY(self_ == NULL)) {
       if (!expected_has_no_thread_) {
         Runtime* runtime = Runtime::Current();
         bool shutting_down = (runtime == NULL) || runtime->IsShuttingDown(nullptr);
         CHECK(shutting_down);
       }
     } else {
       if (old_thread_state_ != thread_state_) {
         if (old_thread_state_ == kRunnable) {
           self_->TransitionFromSuspendedToRunnable();
         } else if (thread_state_ == kRunnable) {
           self_->TransitionFromRunnableToSuspended(old_thread_state_);
         } else {
           // A suspended transition to another effectively suspended transition, ok to use Unsafe.
           self_->SetState(old_thread_state_);
         }
       }
     }
   }

   Thread* Self() const {
     return self_;
   }

  protected:
   // Constructor used by ScopedJniThreadState for an unattached thread that has access to the VM*.
   ScopedThreadStateChange()
       : self_(NULL), thread_state_(kTerminated), old_thread_state_(kTerminated),
         expected_has_no_thread_(true) {}

   Thread* const self_;
   const ThreadState thread_state_;

  private:
   ThreadState old_thread_state_;
   const bool expected_has_no_thread_;

   friend class ScopedObjectAccessUnchecked;
   DISALLOW_COPY_AND_ASSIGN(ScopedThreadStateChange);
 };

 // Assumes we are already runnable.
 class ScopedObjectAccessAlreadyRunnable {
  public:
   Thread* Self() const {
     return self_;
   }

   JNIEnvExt* Env() const {
     return env_;
   }

   JavaVMExt* Vm() const {
     return vm_;
   }

   bool ForceCopy() const {
     return vm_->ForceCopy();
   }

   /*
    * Add a local reference for an object to the indirect reference table associated with the
    * current stack frame.  When the native function returns, the reference will be discarded.
    *
    * We need to allow the same reference to be added multiple times, and cope with NULL.
    *
    * This will be called on otherwise unreferenced objects. We cannot do GC allocations here, and
    * it's best if we don't grab a mutex.
    */
   template<typename T>
   T AddLocalReference(mirror::Object* obj) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     Locks::mutator_lock_->AssertSharedHeld(Self());
     DCHECK(IsRunnable());  // Don't work with raw objects in non-runnable states.
     if (obj == NULL) {
       return NULL;
     }
     DCHECK_NE((reinterpret_cast<uintptr_t>(obj) & 0xffff0000), 0xebad0000);
     return Env()->AddLocalReference<T>(obj);
   }

   template<typename T>
   T Decode(jobject obj) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     Locks::mutator_lock_->AssertSharedHeld(Self());
     DCHECK(IsRunnable());  // Don't work with raw objects in non-runnable states.
     return down_cast<T>(Self()->DecodeJObject(obj));
   }

   mirror::ArtField* DecodeField(jfieldID fid) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     Locks::mutator_lock_->AssertSharedHeld(Self());
     DCHECK(IsRunnable());  // Don't work with raw objects in non-runnable states.
     CHECK(!kMovingFields);
     mirror::ArtField* field = reinterpret_cast<mirror::ArtField*>(fid);
     return ReadBarrier::BarrierForRoot<mirror::ArtField, kWithReadBarrier>(&field);
   }

   jfieldID EncodeField(mirror::ArtField* field) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     Locks::mutator_lock_->AssertSharedHeld(Self());
     DCHECK(IsRunnable());  // Don't work with raw objects in non-runnable states.
     CHECK(!kMovingFields);
     return reinterpret_cast<jfieldID>(field);
   }

   mirror::ArtMethod* DecodeMethod(jmethodID mid) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     Locks::mutator_lock_->AssertSharedHeld(Self());
     DCHECK(IsRunnable());  // Don't work with raw objects in non-runnable states.
     CHECK(!kMovingMethods);
     mirror::ArtMethod* method = reinterpret_cast<mirror::ArtMethod*>(mid);
     return ReadBarrier::BarrierForRoot<mirror::ArtMethod, kWithReadBarrier>(&method);
   }

   jmethodID EncodeMethod(mirror::ArtMethod* method) const
       SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
     Locks::mutator_lock_->AssertSharedHeld(Self());
     DCHECK(IsRunnable());  // Don't work with raw objects in non-runnable states.
     CHECK(!kMovingMethods);
     return reinterpret_cast<jmethodID>(method);
   }

   bool IsRunnable() const {
     return self_->GetState() == kRunnable;
   }

  protected:
   explicit ScopedObjectAccessAlreadyRunnable(JNIEnv* env)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
       : self_(ThreadForEnv(env)), env_(down_cast<JNIEnvExt*>(env)), vm_(env_->vm) {
   }

   explicit ScopedObjectAccessAlreadyRunnable(Thread* self)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
       : self_(self), env_(down_cast<JNIEnvExt*>(self->GetJniEnv())),
         vm_(env_ != nullptr ? env_->vm : nullptr) {
   }

   // Used when we want a scoped JNI thread state but have no thread/JNIEnv. Consequently doesn't
   // change into Runnable or acquire a share on the mutator_lock_.
   explicit ScopedObjectAccessAlreadyRunnable(JavaVM* vm)
       : self_(nullptr), env_(nullptr), vm_(down_cast<JavaVMExt*>(vm)) {}

   // Here purely to force inlining.
   ~ScopedObjectAccessAlreadyRunnable() ALWAYS_INLINE {
   }

   // Self thread, can be null.
   Thread* const self_;
   // The full JNIEnv.
   JNIEnvExt* const env_;
   // The full JavaVM.
   JavaVMExt* const vm_;
 };

 // Entry/exit processing for transitions from Native to Runnable (ie within JNI functions).
 //
 // This class performs the necessary thread state switching to and from Runnable and lets us
 // amortize the cost of working out the current thread. Additionally it lets us check (and repair)
 // apps that are using a JNIEnv on the wrong thread. The class also decodes and encodes Objects
 // into jobjects via methods of this class. Performing this here enforces the Runnable thread state
 // for use of Object, thereby inhibiting the Object being modified by GC whilst native or VM code
 // is also manipulating the Object.
 //
 // The destructor transitions back to the previous thread state, typically Native. In this state
 // GC and thread suspension may occur.
 //
 // For annotalysis the subclass ScopedObjectAccess (below) makes it explicit that a shared of
 // the mutator_lock_ will be acquired on construction.
 class ScopedObjectAccessUnchecked : public ScopedObjectAccessAlreadyRunnable {
  public:
   explicit ScopedObjectAccessUnchecked(JNIEnv* env)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
       : ScopedObjectAccessAlreadyRunnable(env), tsc_(Self(), kRunnable) {
     Self()->VerifyStack();
     Locks::mutator_lock_->AssertSharedHeld(Self());
   }

   explicit ScopedObjectAccessUnchecked(Thread* self)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
       : ScopedObjectAccessAlreadyRunnable(self), tsc_(self, kRunnable) {
     Self()->VerifyStack();
     Locks::mutator_lock_->AssertSharedHeld(Self());
   }

   // Used when we want a scoped JNI thread state but have no thread/JNIEnv. Consequently doesn't
   // change into Runnable or acquire a share on the mutator_lock_.
   explicit ScopedObjectAccessUnchecked(JavaVM* vm) ALWAYS_INLINE
       : ScopedObjectAccessAlreadyRunnable(vm), tsc_() {}

  private:
   // The scoped thread state change makes sure that we are runnable and restores the thread state
   // in the destructor.
   const ScopedThreadStateChange tsc_;

   DISALLOW_COPY_AND_ASSIGN(ScopedObjectAccessUnchecked);
 };

 // Annotalysis helping variant of the above.
 class ScopedObjectAccess : public ScopedObjectAccessUnchecked {
  public:
   explicit ScopedObjectAccess(JNIEnv* env)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_)
       SHARED_LOCK_FUNCTION(Locks::mutator_lock_) ALWAYS_INLINE
       : ScopedObjectAccessUnchecked(env) {
   }

   explicit ScopedObjectAccess(Thread* self)
       LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_)
       SHARED_LOCK_FUNCTION(Locks::mutator_lock_) ALWAYS_INLINE
       : ScopedObjectAccessUnchecked(self) {
   }

   ~ScopedObjectAccess() UNLOCK_FUNCTION(Locks::mutator_lock_) ALWAYS_INLINE {
     // Base class will release share of lock. Invoked after this destructor.
   }

  private:
   // TODO: remove this constructor. It is used by check JNI's ScopedCheck to make it believe that
   //       routines operating with just a VM are sound, they are not, but when you have just a VM
   //       you cannot call the unsound routines.
   explicit ScopedObjectAccess(JavaVM* vm)
       SHARED_LOCK_FUNCTION(Locks::mutator_lock_)
       : ScopedObjectAccessUnchecked(vm) {}

   friend class ScopedCheck;
   DISALLOW_COPY_AND_ASSIGN(ScopedObjectAccess);
 };

 }  // namespace art

 #endif  // ART_RUNTIME_SCOPED_THREAD_STATE_CHANGE_H_
	/*
	* Copyright (C) 2012 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.
	*/

	#ifndef ART_RUNTIME_SCOPED_THREAD_STATE_CHANGE_H_
	#define ART_RUNTIME_SCOPED_THREAD_STATE_CHANGE_H_

	#include "base/casts.h"
	#include "java_vm_ext.h"
	#include "jni_env_ext-inl.h"
	#include "mirror/art_field.h"
	#include "read_barrier.h"
	#include "thread-inl.h"
	#include "verify_object.h"

	namespace art {

	// Scoped change into and out of a particular state. Handles Runnable transitions that require
	// more complicated suspension checking. The subclasses ScopedObjectAccessUnchecked and
	// ScopedObjectAccess are used to handle the change into Runnable to Get direct access to objects,
	// the unchecked variant doesn't aid annotalysis.
	class ScopedThreadStateChange {
	public:
	ScopedThreadStateChange(Thread* self, ThreadState new_thread_state)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
	: self_(self), thread_state_(new_thread_state), expected_has_no_thread_(false) {
	if (UNLIKELY(self_ == NULL)) {
	// Value chosen arbitrarily and won't be used in the destructor since thread_ == NULL.
	old_thread_state_ = kTerminated;
	Runtime* runtime = Runtime::Current();
	CHECK(runtime == NULL \|\| !runtime->IsStarted() \|\| runtime->IsShuttingDown(self_));
	} else {
	DCHECK_EQ(self, Thread::Current());
	// Read state without locks, ok as state is effectively thread local and we're not interested
	// in the suspend count (this will be handled in the runnable transitions).
	old_thread_state_ = self->GetState();
	if (old_thread_state_ != new_thread_state) {
	if (new_thread_state == kRunnable) {
	self_->TransitionFromSuspendedToRunnable();
	} else if (old_thread_state_ == kRunnable) {
	self_->TransitionFromRunnableToSuspended(new_thread_state);
	} else {
	// A suspended transition to another effectively suspended transition, ok to use Unsafe.
	self_->SetState(new_thread_state);
	}
	}
	}
	}

	~ScopedThreadStateChange() LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE {
	if (UNLIKELY(self_ == NULL)) {
	if (!expected_has_no_thread_) {
	Runtime* runtime = Runtime::Current();
	bool shutting_down = (runtime == NULL) \|\| runtime->IsShuttingDown(nullptr);
	CHECK(shutting_down);
	}
	} else {
	if (old_thread_state_ != thread_state_) {
	if (old_thread_state_ == kRunnable) {
	self_->TransitionFromSuspendedToRunnable();
	} else if (thread_state_ == kRunnable) {
	self_->TransitionFromRunnableToSuspended(old_thread_state_);
	} else {
	// A suspended transition to another effectively suspended transition, ok to use Unsafe.
	self_->SetState(old_thread_state_);
	}
	}
	}
	}

	Thread* Self() const {
	return self_;
	}

	protected:
	// Constructor used by ScopedJniThreadState for an unattached thread that has access to the VM*.
	ScopedThreadStateChange()
	: self_(NULL), thread_state_(kTerminated), old_thread_state_(kTerminated),
	expected_has_no_thread_(true) {}

	Thread* const self_;
	const ThreadState thread_state_;

	private:
	ThreadState old_thread_state_;
	const bool expected_has_no_thread_;

	friend class ScopedObjectAccessUnchecked;
	DISALLOW_COPY_AND_ASSIGN(ScopedThreadStateChange);
	};

	// Assumes we are already runnable.
	class ScopedObjectAccessAlreadyRunnable {
	public:
	Thread* Self() const {
	return self_;
	}

	JNIEnvExt* Env() const {
	return env_;
	}

	JavaVMExt* Vm() const {
	return vm_;
	}

	bool ForceCopy() const {
	return vm_->ForceCopy();
	}

	/*
	* Add a local reference for an object to the indirect reference table associated with the
	* current stack frame. When the native function returns, the reference will be discarded.
	*
	* We need to allow the same reference to be added multiple times, and cope with NULL.
	*
	* This will be called on otherwise unreferenced objects. We cannot do GC allocations here, and
	* it's best if we don't grab a mutex.
	*/
	template<typename T>
	T AddLocalReference(mirror::Object* obj) const SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	Locks::mutator_lock_->AssertSharedHeld(Self());
	DCHECK(IsRunnable()); // Don't work with raw objects in non-runnable states.
	if (obj == NULL) {
	return NULL;
	}
	DCHECK_NE((reinterpret_cast<uintptr_t>(obj) & 0xffff0000), 0xebad0000);
	return Env()->AddLocalReference<T>(obj);
	}

	template<typename T>
	T Decode(jobject obj) const
	SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	Locks::mutator_lock_->AssertSharedHeld(Self());
	DCHECK(IsRunnable()); // Don't work with raw objects in non-runnable states.
	return down_cast<T>(Self()->DecodeJObject(obj));
	}

	mirror::ArtField* DecodeField(jfieldID fid) const
	SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	Locks::mutator_lock_->AssertSharedHeld(Self());
	DCHECK(IsRunnable()); // Don't work with raw objects in non-runnable states.
	CHECK(!kMovingFields);
	mirror::ArtField* field = reinterpret_cast<mirror::ArtField*>(fid);
	return ReadBarrier::BarrierForRoot<mirror::ArtField, kWithReadBarrier>(&field);
	}

	jfieldID EncodeField(mirror::ArtField* field) const
	SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	Locks::mutator_lock_->AssertSharedHeld(Self());
	DCHECK(IsRunnable()); // Don't work with raw objects in non-runnable states.
	CHECK(!kMovingFields);
	return reinterpret_cast<jfieldID>(field);
	}

	mirror::ArtMethod* DecodeMethod(jmethodID mid) const
	SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	Locks::mutator_lock_->AssertSharedHeld(Self());
	DCHECK(IsRunnable()); // Don't work with raw objects in non-runnable states.
	CHECK(!kMovingMethods);
	mirror::ArtMethod* method = reinterpret_cast<mirror::ArtMethod*>(mid);
	return ReadBarrier::BarrierForRoot<mirror::ArtMethod, kWithReadBarrier>(&method);
	}

	jmethodID EncodeMethod(mirror::ArtMethod* method) const
	SHARED_LOCKS_REQUIRED(Locks::mutator_lock_) {
	Locks::mutator_lock_->AssertSharedHeld(Self());
	DCHECK(IsRunnable()); // Don't work with raw objects in non-runnable states.
	CHECK(!kMovingMethods);
	return reinterpret_cast<jmethodID>(method);
	}

	bool IsRunnable() const {
	return self_->GetState() == kRunnable;
	}

	protected:
	explicit ScopedObjectAccessAlreadyRunnable(JNIEnv* env)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
	: self_(ThreadForEnv(env)), env_(down_cast<JNIEnvExt*>(env)), vm_(env_->vm) {
	}

	explicit ScopedObjectAccessAlreadyRunnable(Thread* self)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
	: self_(self), env_(down_cast<JNIEnvExt*>(self->GetJniEnv())),
	vm_(env_ != nullptr ? env_->vm : nullptr) {
	}

	// Used when we want a scoped JNI thread state but have no thread/JNIEnv. Consequently doesn't
	// change into Runnable or acquire a share on the mutator_lock_.
	explicit ScopedObjectAccessAlreadyRunnable(JavaVM* vm)
	: self_(nullptr), env_(nullptr), vm_(down_cast<JavaVMExt*>(vm)) {}

	// Here purely to force inlining.
	~ScopedObjectAccessAlreadyRunnable() ALWAYS_INLINE {
	}

	// Self thread, can be null.
	Thread* const self_;
	// The full JNIEnv.
	JNIEnvExt* const env_;
	// The full JavaVM.
	JavaVMExt* const vm_;
	};

	// Entry/exit processing for transitions from Native to Runnable (ie within JNI functions).
	//
	// This class performs the necessary thread state switching to and from Runnable and lets us
	// amortize the cost of working out the current thread. Additionally it lets us check (and repair)
	// apps that are using a JNIEnv on the wrong thread. The class also decodes and encodes Objects
	// into jobjects via methods of this class. Performing this here enforces the Runnable thread state
	// for use of Object, thereby inhibiting the Object being modified by GC whilst native or VM code
	// is also manipulating the Object.
	//
	// The destructor transitions back to the previous thread state, typically Native. In this state
	// GC and thread suspension may occur.
	//
	// For annotalysis the subclass ScopedObjectAccess (below) makes it explicit that a shared of
	// the mutator_lock_ will be acquired on construction.
	class ScopedObjectAccessUnchecked : public ScopedObjectAccessAlreadyRunnable {
	public:
	explicit ScopedObjectAccessUnchecked(JNIEnv* env)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
	: ScopedObjectAccessAlreadyRunnable(env), tsc_(Self(), kRunnable) {
	Self()->VerifyStack();
	Locks::mutator_lock_->AssertSharedHeld(Self());
	}

	explicit ScopedObjectAccessUnchecked(Thread* self)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_) ALWAYS_INLINE
	: ScopedObjectAccessAlreadyRunnable(self), tsc_(self, kRunnable) {
	Self()->VerifyStack();
	Locks::mutator_lock_->AssertSharedHeld(Self());
	}

	// Used when we want a scoped JNI thread state but have no thread/JNIEnv. Consequently doesn't
	// change into Runnable or acquire a share on the mutator_lock_.
	explicit ScopedObjectAccessUnchecked(JavaVM* vm) ALWAYS_INLINE
	: ScopedObjectAccessAlreadyRunnable(vm), tsc_() {}

	private:
	// The scoped thread state change makes sure that we are runnable and restores the thread state
	// in the destructor.
	const ScopedThreadStateChange tsc_;

	DISALLOW_COPY_AND_ASSIGN(ScopedObjectAccessUnchecked);
	};

	// Annotalysis helping variant of the above.
	class ScopedObjectAccess : public ScopedObjectAccessUnchecked {
	public:
	explicit ScopedObjectAccess(JNIEnv* env)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_)
	SHARED_LOCK_FUNCTION(Locks::mutator_lock_) ALWAYS_INLINE
	: ScopedObjectAccessUnchecked(env) {
	}

	explicit ScopedObjectAccess(Thread* self)
	LOCKS_EXCLUDED(Locks::thread_suspend_count_lock_)
	SHARED_LOCK_FUNCTION(Locks::mutator_lock_) ALWAYS_INLINE
	: ScopedObjectAccessUnchecked(self) {
	}

	~ScopedObjectAccess() UNLOCK_FUNCTION(Locks::mutator_lock_) ALWAYS_INLINE {
	// Base class will release share of lock. Invoked after this destructor.
	}

	private:
	// TODO: remove this constructor. It is used by check JNI's ScopedCheck to make it believe that
	// routines operating with just a VM are sound, they are not, but when you have just a VM
	// you cannot call the unsound routines.
	explicit ScopedObjectAccess(JavaVM* vm)
	SHARED_LOCK_FUNCTION(Locks::mutator_lock_)
	: ScopedObjectAccessUnchecked(vm) {}

	friend class ScopedCheck;
	DISALLOW_COPY_AND_ASSIGN(ScopedObjectAccess);
	};

	} // namespace art

	#endif // ART_RUNTIME_SCOPED_THREAD_STATE_CHANGE_H_