runtime/monitor.h - platform/art - Gitiles

 /*
  * Copyright (C) 2008 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_MONITOR_H_
 #define ART_RUNTIME_MONITOR_H_

 #include <pthread.h>
 #include <stdint.h>
 #include <stdlib.h>

 #include <iosfwd>
 #include <list>
 #include <vector>

 #include "atomic.h"
 #include "base/allocator.h"
 #include "base/mutex.h"
 #include "gc_root.h"
 #include "lock_word.h"
 #include "read_barrier_option.h"
 #include "runtime_callbacks.h"
 #include "thread_state.h"

 namespace art {

 class ArtMethod;
 class IsMarkedVisitor;
 class LockWord;
 template<class T> class Handle;
 class StackVisitor;
 class Thread;
 typedef uint32_t MonitorId;

 namespace mirror {
 class Object;
 }  // namespace mirror

 enum class LockReason {
   kForWait,
   kForLock,
 };

 class Monitor {
  public:
   // The default number of spins that are done before thread suspension is used to forcibly inflate
   // a lock word. See Runtime::max_spins_before_thin_lock_inflation_.
   constexpr static size_t kDefaultMaxSpinsBeforeThinLockInflation = 50;

   ~Monitor();

   static void Init(uint32_t lock_profiling_threshold, uint32_t stack_dump_lock_profiling_threshold);

   // Return the thread id of the lock owner or 0 when there is no owner.
   static uint32_t GetLockOwnerThreadId(mirror::Object* obj)
       NO_THREAD_SAFETY_ANALYSIS;  // TODO: Reading lock owner without holding lock is racy.

   // NO_THREAD_SAFETY_ANALYSIS for mon->Lock.
   static mirror::Object* MonitorEnter(Thread* thread, mirror::Object* obj, bool trylock)
       EXCLUSIVE_LOCK_FUNCTION(obj)
       NO_THREAD_SAFETY_ANALYSIS
       REQUIRES(!Roles::uninterruptible_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // NO_THREAD_SAFETY_ANALYSIS for mon->Unlock.
   static bool MonitorExit(Thread* thread, mirror::Object* obj)
       NO_THREAD_SAFETY_ANALYSIS
       REQUIRES(!Roles::uninterruptible_)
       REQUIRES_SHARED(Locks::mutator_lock_)
       UNLOCK_FUNCTION(obj);

   static void Notify(Thread* self, mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) {
     DoNotify(self, obj, false);
   }
   static void NotifyAll(Thread* self, mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) {
     DoNotify(self, obj, true);
   }

   // Object.wait().  Also called for class init.
   // NO_THREAD_SAFETY_ANALYSIS for mon->Wait.
   static void Wait(Thread* self, mirror::Object* obj, int64_t ms, int32_t ns,
                    bool interruptShouldThrow, ThreadState why)
       REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS;

   static ThreadState FetchState(const Thread* thread,
                                 /* out */ mirror::Object** monitor_object,
                                 /* out */ uint32_t* lock_owner_tid)
       REQUIRES(!Locks::thread_suspend_count_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Used to implement JDWP's ThreadReference.CurrentContendedMonitor.
   static mirror::Object* GetContendedMonitor(Thread* thread)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Calls 'callback' once for each lock held in the single stack frame represented by
   // the current state of 'stack_visitor'.
   // The abort_on_failure flag allows to not die when the state of the runtime is unorderly. This
   // is necessary when we have already aborted but want to dump the stack as much as we can.
   static void VisitLocks(StackVisitor* stack_visitor, void (*callback)(mirror::Object*, void*),
                          void* callback_context, bool abort_on_failure = true)
       REQUIRES_SHARED(Locks::mutator_lock_);

   static bool IsValidLockWord(LockWord lock_word);

   template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
   mirror::Object* GetObject() REQUIRES_SHARED(Locks::mutator_lock_) {
     return obj_.Read<kReadBarrierOption>();
   }

   void SetObject(mirror::Object* object);

   Thread* GetOwner() const NO_THREAD_SAFETY_ANALYSIS {
     return owner_;
   }

   int32_t GetHashCode();

   bool IsLocked() REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_lock_);

   bool HasHashCode() const {
     return hash_code_.LoadRelaxed() != 0;
   }

   MonitorId GetMonitorId() const {
     return monitor_id_;
   }

   // Inflate the lock on obj. May fail to inflate for spurious reasons, always re-check.
   static void InflateThinLocked(Thread* self, Handle<mirror::Object> obj, LockWord lock_word,
                                 uint32_t hash_code) REQUIRES_SHARED(Locks::mutator_lock_);

   // Not exclusive because ImageWriter calls this during a Heap::VisitObjects() that
   // does not allow a thread suspension in the middle. TODO: maybe make this exclusive.
   // NO_THREAD_SAFETY_ANALYSIS for monitor->monitor_lock_.
   static bool Deflate(Thread* self, mirror::Object* obj)
       REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS;

 #ifndef __LP64__
   void* operator new(size_t size) {
     // Align Monitor* as per the monitor ID field size in the lock word.
     void* result;
     int error = posix_memalign(&result, LockWord::kMonitorIdAlignment, size);
     CHECK_EQ(error, 0) << strerror(error);
     return result;
   }

   void operator delete(void* ptr) {
     free(ptr);
   }
 #endif

  private:
   Monitor(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code)
       REQUIRES_SHARED(Locks::mutator_lock_);
   Monitor(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code, MonitorId id)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Install the monitor into its object, may fail if another thread installs a different monitor
   // first.
   bool Install(Thread* self)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Links a thread into a monitor's wait set.  The monitor lock must be held by the caller of this
   // routine.
   void AppendToWaitSet(Thread* thread) REQUIRES(monitor_lock_);

   // Unlinks a thread from a monitor's wait set.  The monitor lock must be held by the caller of
   // this routine.
   void RemoveFromWaitSet(Thread* thread) REQUIRES(monitor_lock_);

   // Changes the shape of a monitor from thin to fat, preserving the internal lock state. The
   // calling thread must own the lock or the owner must be suspended. There's a race with other
   // threads inflating the lock, installing hash codes and spurious failures. The caller should
   // re-read the lock word following the call.
   static void Inflate(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code)
       REQUIRES_SHARED(Locks::mutator_lock_)
       NO_THREAD_SAFETY_ANALYSIS;  // For m->Install(self)

   void LogContentionEvent(Thread* self,
                           uint32_t wait_ms,
                           uint32_t sample_percent,
                           ArtMethod* owner_method,
                           uint32_t owner_dex_pc)
       REQUIRES_SHARED(Locks::mutator_lock_);

   static void FailedUnlock(mirror::Object* obj,
                            uint32_t expected_owner_thread_id,
                            uint32_t found_owner_thread_id,
                            Monitor* mon)
       REQUIRES(!Locks::thread_list_lock_,
                !monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Try to lock without blocking, returns true if we acquired the lock.
   bool TryLock(Thread* self)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);
   // Variant for already holding the monitor lock.
   bool TryLockLocked(Thread* self)
       REQUIRES(monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   template<LockReason reason = LockReason::kForLock>
   void Lock(Thread* self)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   bool Unlock(Thread* thread)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   static void DoNotify(Thread* self, mirror::Object* obj, bool notify_all)
       REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS;  // For mon->Notify.

   void Notify(Thread* self)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   void NotifyAll(Thread* self)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   static std::string PrettyContentionInfo(const std::string& owner_name,
                                           pid_t owner_tid,
                                           ArtMethod* owners_method,
                                           uint32_t owners_dex_pc,
                                           size_t num_waiters)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Wait on a monitor until timeout, interrupt, or notification.  Used for Object.wait() and
   // (somewhat indirectly) Thread.sleep() and Thread.join().
   //
   // If another thread calls Thread.interrupt(), we throw InterruptedException and return
   // immediately if one of the following are true:
   //  - blocked in wait(), wait(long), or wait(long, int) methods of Object
   //  - blocked in join(), join(long), or join(long, int) methods of Thread
   //  - blocked in sleep(long), or sleep(long, int) methods of Thread
   // Otherwise, we set the "interrupted" flag.
   //
   // Checks to make sure that "ns" is in the range 0-999999 (i.e. fractions of a millisecond) and
   // throws the appropriate exception if it isn't.
   //
   // The spec allows "spurious wakeups", and recommends that all code using Object.wait() do so in
   // a loop.  This appears to derive from concerns about pthread_cond_wait() on multiprocessor
   // systems.  Some commentary on the web casts doubt on whether these can/should occur.
   //
   // Since we're allowed to wake up "early", we clamp extremely long durations to return at the end
   // of the 32-bit time epoch.
   void Wait(Thread* self, int64_t msec, int32_t nsec, bool interruptShouldThrow, ThreadState why)
       REQUIRES(!monitor_lock_)
       REQUIRES_SHARED(Locks::mutator_lock_);

   // Translates the provided method and pc into its declaring class' source file and line number.
   static void TranslateLocation(ArtMethod* method, uint32_t pc,
                                 const char** source_file,
                                 int32_t* line_number)
       REQUIRES_SHARED(Locks::mutator_lock_);

   uint32_t GetOwnerThreadId() REQUIRES(!monitor_lock_);

   // Support for systrace output of monitor operations.
   ALWAYS_INLINE static void AtraceMonitorLock(Thread* self,
                                               mirror::Object* obj,
                                               bool is_wait)
       REQUIRES_SHARED(Locks::mutator_lock_);
   static void AtraceMonitorLockImpl(Thread* self,
                                     mirror::Object* obj,
                                     bool is_wait)
       REQUIRES_SHARED(Locks::mutator_lock_);
   ALWAYS_INLINE static void AtraceMonitorUnlock();

   static uint32_t lock_profiling_threshold_;
   static uint32_t stack_dump_lock_profiling_threshold_;

   Mutex monitor_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;

   ConditionVariable monitor_contenders_ GUARDED_BY(monitor_lock_);

   // Number of people waiting on the condition.
   size_t num_waiters_ GUARDED_BY(monitor_lock_);

   // Which thread currently owns the lock?
   Thread* volatile owner_ GUARDED_BY(monitor_lock_);

   // Owner's recursive lock depth.
   int lock_count_ GUARDED_BY(monitor_lock_);

   // What object are we part of. This is a weak root. Do not access
   // this directly, use GetObject() to read it so it will be guarded
   // by a read barrier.
   GcRoot<mirror::Object> obj_;

   // Threads currently waiting on this monitor.
   Thread* wait_set_ GUARDED_BY(monitor_lock_);

   // Stored object hash code, generated lazily by GetHashCode.
   AtomicInteger hash_code_;

   // Method and dex pc where the lock owner acquired the lock, used when lock
   // sampling is enabled. locking_method_ may be null if the lock is currently
   // unlocked, or if the lock is acquired by the system when the stack is empty.
   ArtMethod* locking_method_ GUARDED_BY(monitor_lock_);
   uint32_t locking_dex_pc_ GUARDED_BY(monitor_lock_);

   // The denser encoded version of this monitor as stored in the lock word.
   MonitorId monitor_id_;

 #ifdef __LP64__
   // Free list for monitor pool.
   Monitor* next_free_ GUARDED_BY(Locks::allocated_monitor_ids_lock_);
 #endif

   friend class MonitorInfo;
   friend class MonitorList;
   friend class MonitorPool;
   friend class mirror::Object;
   DISALLOW_COPY_AND_ASSIGN(Monitor);
 };

 class MonitorList {
  public:
   MonitorList();
   ~MonitorList();

   void Add(Monitor* m) REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_list_lock_);

   void SweepMonitorList(IsMarkedVisitor* visitor)
       REQUIRES(!monitor_list_lock_) REQUIRES_SHARED(Locks::mutator_lock_);
   void DisallowNewMonitors() REQUIRES(!monitor_list_lock_);
   void AllowNewMonitors() REQUIRES(!monitor_list_lock_);
   void BroadcastForNewMonitors() REQUIRES(!monitor_list_lock_);
   // Returns how many monitors were deflated.
   size_t DeflateMonitors() REQUIRES(!monitor_list_lock_) REQUIRES(Locks::mutator_lock_);
   size_t Size() REQUIRES(!monitor_list_lock_);

   typedef std::list<Monitor*, TrackingAllocator<Monitor*, kAllocatorTagMonitorList>> Monitors;

  private:
   // During sweeping we may free an object and on a separate thread have an object created using
   // the newly freed memory. That object may then have its lock-word inflated and a monitor created.
   // If we allow new monitor registration during sweeping this monitor may be incorrectly freed as
   // the object wasn't marked when sweeping began.
   bool allow_new_monitors_ GUARDED_BY(monitor_list_lock_);
   Mutex monitor_list_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
   ConditionVariable monitor_add_condition_ GUARDED_BY(monitor_list_lock_);
   Monitors list_ GUARDED_BY(monitor_list_lock_);

   friend class Monitor;
   DISALLOW_COPY_AND_ASSIGN(MonitorList);
 };

 // Collects information about the current state of an object's monitor.
 // This is very unsafe, and must only be called when all threads are suspended.
 // For use only by the JDWP implementation.
 class MonitorInfo {
  public:
   MonitorInfo() : owner_(nullptr), entry_count_(0) {}
   MonitorInfo(const MonitorInfo&) = default;
   MonitorInfo& operator=(const MonitorInfo&) = default;
   explicit MonitorInfo(mirror::Object* o) REQUIRES(Locks::mutator_lock_);

   Thread* owner_;
   size_t entry_count_;
   std::vector<Thread*> waiters_;
 };

 }  // namespace art

 #endif  // ART_RUNTIME_MONITOR_H_
	/*
	* Copyright (C) 2008 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_MONITOR_H_
	#define ART_RUNTIME_MONITOR_H_

	#include <pthread.h>
	#include <stdint.h>
	#include <stdlib.h>

	#include <iosfwd>
	#include <list>
	#include <vector>

	#include "atomic.h"
	#include "base/allocator.h"
	#include "base/mutex.h"
	#include "gc_root.h"
	#include "lock_word.h"
	#include "read_barrier_option.h"
	#include "runtime_callbacks.h"
	#include "thread_state.h"

	namespace art {

	class ArtMethod;
	class IsMarkedVisitor;
	class LockWord;
	template<class T> class Handle;
	class StackVisitor;
	class Thread;
	typedef uint32_t MonitorId;

	namespace mirror {
	class Object;
	} // namespace mirror

	enum class LockReason {
	kForWait,
	kForLock,
	};

	class Monitor {
	public:
	// The default number of spins that are done before thread suspension is used to forcibly inflate
	// a lock word. See Runtime::max_spins_before_thin_lock_inflation_.
	constexpr static size_t kDefaultMaxSpinsBeforeThinLockInflation = 50;

	~Monitor();

	static void Init(uint32_t lock_profiling_threshold, uint32_t stack_dump_lock_profiling_threshold);

	// Return the thread id of the lock owner or 0 when there is no owner.
	static uint32_t GetLockOwnerThreadId(mirror::Object* obj)
	NO_THREAD_SAFETY_ANALYSIS; // TODO: Reading lock owner without holding lock is racy.

	// NO_THREAD_SAFETY_ANALYSIS for mon->Lock.
	static mirror::Object* MonitorEnter(Thread* thread, mirror::Object* obj, bool trylock)
	EXCLUSIVE_LOCK_FUNCTION(obj)
	NO_THREAD_SAFETY_ANALYSIS
	REQUIRES(!Roles::uninterruptible_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// NO_THREAD_SAFETY_ANALYSIS for mon->Unlock.
	static bool MonitorExit(Thread* thread, mirror::Object* obj)
	NO_THREAD_SAFETY_ANALYSIS
	REQUIRES(!Roles::uninterruptible_)
	REQUIRES_SHARED(Locks::mutator_lock_)
	UNLOCK_FUNCTION(obj);

	static void Notify(Thread* self, mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) {
	DoNotify(self, obj, false);
	}
	static void NotifyAll(Thread* self, mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) {
	DoNotify(self, obj, true);
	}

	// Object.wait(). Also called for class init.
	// NO_THREAD_SAFETY_ANALYSIS for mon->Wait.
	static void Wait(Thread* self, mirror::Object* obj, int64_t ms, int32_t ns,
	bool interruptShouldThrow, ThreadState why)
	REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS;

	static ThreadState FetchState(const Thread* thread,
	/* out / mirror::Object* monitor_object,
	/* out / uint32_t lock_owner_tid)
	REQUIRES(!Locks::thread_suspend_count_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Used to implement JDWP's ThreadReference.CurrentContendedMonitor.
	static mirror::Object* GetContendedMonitor(Thread* thread)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Calls 'callback' once for each lock held in the single stack frame represented by
	// the current state of 'stack_visitor'.
	// The abort_on_failure flag allows to not die when the state of the runtime is unorderly. This
	// is necessary when we have already aborted but want to dump the stack as much as we can.
	static void VisitLocks(StackVisitor* stack_visitor, void (callback)(mirror::Object, void*),
	void* callback_context, bool abort_on_failure = true)
	REQUIRES_SHARED(Locks::mutator_lock_);

	static bool IsValidLockWord(LockWord lock_word);

	template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier>
	mirror::Object* GetObject() REQUIRES_SHARED(Locks::mutator_lock_) {
	return obj_.Read<kReadBarrierOption>();
	}

	void SetObject(mirror::Object* object);

	Thread* GetOwner() const NO_THREAD_SAFETY_ANALYSIS {
	return owner_;
	}

	int32_t GetHashCode();

	bool IsLocked() REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_lock_);

	bool HasHashCode() const {
	return hash_code_.LoadRelaxed() != 0;
	}

	MonitorId GetMonitorId() const {
	return monitor_id_;
	}

	// Inflate the lock on obj. May fail to inflate for spurious reasons, always re-check.
	static void InflateThinLocked(Thread* self, Handle<mirror::Object> obj, LockWord lock_word,
	uint32_t hash_code) REQUIRES_SHARED(Locks::mutator_lock_);

	// Not exclusive because ImageWriter calls this during a Heap::VisitObjects() that
	// does not allow a thread suspension in the middle. TODO: maybe make this exclusive.
	// NO_THREAD_SAFETY_ANALYSIS for monitor->monitor_lock_.
	static bool Deflate(Thread* self, mirror::Object* obj)
	REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS;

	#ifndef __LP64__
	void* operator new(size_t size) {
	// Align Monitor* as per the monitor ID field size in the lock word.
	void* result;
	int error = posix_memalign(&result, LockWord::kMonitorIdAlignment, size);
	CHECK_EQ(error, 0) << strerror(error);
	return result;
	}

	void operator delete(void* ptr) {
	free(ptr);
	}
	#endif

	private:
	Monitor(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code)
	REQUIRES_SHARED(Locks::mutator_lock_);
	Monitor(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code, MonitorId id)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Install the monitor into its object, may fail if another thread installs a different monitor
	// first.
	bool Install(Thread* self)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Links a thread into a monitor's wait set. The monitor lock must be held by the caller of this
	// routine.
	void AppendToWaitSet(Thread* thread) REQUIRES(monitor_lock_);

	// Unlinks a thread from a monitor's wait set. The monitor lock must be held by the caller of
	// this routine.
	void RemoveFromWaitSet(Thread* thread) REQUIRES(monitor_lock_);

	// Changes the shape of a monitor from thin to fat, preserving the internal lock state. The
	// calling thread must own the lock or the owner must be suspended. There's a race with other
	// threads inflating the lock, installing hash codes and spurious failures. The caller should
	// re-read the lock word following the call.
	static void Inflate(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code)
	REQUIRES_SHARED(Locks::mutator_lock_)
	NO_THREAD_SAFETY_ANALYSIS; // For m->Install(self)

	void LogContentionEvent(Thread* self,
	uint32_t wait_ms,
	uint32_t sample_percent,
	ArtMethod* owner_method,
	uint32_t owner_dex_pc)
	REQUIRES_SHARED(Locks::mutator_lock_);

	static void FailedUnlock(mirror::Object* obj,
	uint32_t expected_owner_thread_id,
	uint32_t found_owner_thread_id,
	Monitor* mon)
	REQUIRES(!Locks::thread_list_lock_,
	!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Try to lock without blocking, returns true if we acquired the lock.
	bool TryLock(Thread* self)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);
	// Variant for already holding the monitor lock.
	bool TryLockLocked(Thread* self)
	REQUIRES(monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	template<LockReason reason = LockReason::kForLock>
	void Lock(Thread* self)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	bool Unlock(Thread* thread)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	static void DoNotify(Thread* self, mirror::Object* obj, bool notify_all)
	REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS; // For mon->Notify.

	void Notify(Thread* self)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	void NotifyAll(Thread* self)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	static std::string PrettyContentionInfo(const std::string& owner_name,
	pid_t owner_tid,
	ArtMethod* owners_method,
	uint32_t owners_dex_pc,
	size_t num_waiters)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Wait on a monitor until timeout, interrupt, or notification. Used for Object.wait() and
	// (somewhat indirectly) Thread.sleep() and Thread.join().
	//
	// If another thread calls Thread.interrupt(), we throw InterruptedException and return
	// immediately if one of the following are true:
	// - blocked in wait(), wait(long), or wait(long, int) methods of Object
	// - blocked in join(), join(long), or join(long, int) methods of Thread
	// - blocked in sleep(long), or sleep(long, int) methods of Thread
	// Otherwise, we set the "interrupted" flag.
	//
	// Checks to make sure that "ns" is in the range 0-999999 (i.e. fractions of a millisecond) and
	// throws the appropriate exception if it isn't.
	//
	// The spec allows "spurious wakeups", and recommends that all code using Object.wait() do so in
	// a loop. This appears to derive from concerns about pthread_cond_wait() on multiprocessor
	// systems. Some commentary on the web casts doubt on whether these can/should occur.
	//
	// Since we're allowed to wake up "early", we clamp extremely long durations to return at the end
	// of the 32-bit time epoch.
	void Wait(Thread* self, int64_t msec, int32_t nsec, bool interruptShouldThrow, ThreadState why)
	REQUIRES(!monitor_lock_)
	REQUIRES_SHARED(Locks::mutator_lock_);

	// Translates the provided method and pc into its declaring class' source file and line number.
	static void TranslateLocation(ArtMethod* method, uint32_t pc,
	const char** source_file,
	int32_t* line_number)
	REQUIRES_SHARED(Locks::mutator_lock_);

	uint32_t GetOwnerThreadId() REQUIRES(!monitor_lock_);

	// Support for systrace output of monitor operations.
	ALWAYS_INLINE static void AtraceMonitorLock(Thread* self,
	mirror::Object* obj,
	bool is_wait)
	REQUIRES_SHARED(Locks::mutator_lock_);
	static void AtraceMonitorLockImpl(Thread* self,
	mirror::Object* obj,
	bool is_wait)
	REQUIRES_SHARED(Locks::mutator_lock_);
	ALWAYS_INLINE static void AtraceMonitorUnlock();

	static uint32_t lock_profiling_threshold_;
	static uint32_t stack_dump_lock_profiling_threshold_;

	Mutex monitor_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;

	ConditionVariable monitor_contenders_ GUARDED_BY(monitor_lock_);

	// Number of people waiting on the condition.
	size_t num_waiters_ GUARDED_BY(monitor_lock_);

	// Which thread currently owns the lock?
	Thread* volatile owner_ GUARDED_BY(monitor_lock_);

	// Owner's recursive lock depth.
	int lock_count_ GUARDED_BY(monitor_lock_);

	// What object are we part of. This is a weak root. Do not access
	// this directly, use GetObject() to read it so it will be guarded
	// by a read barrier.
	GcRoot<mirror::Object> obj_;

	// Threads currently waiting on this monitor.
	Thread* wait_set_ GUARDED_BY(monitor_lock_);

	// Stored object hash code, generated lazily by GetHashCode.
	AtomicInteger hash_code_;

	// Method and dex pc where the lock owner acquired the lock, used when lock
	// sampling is enabled. locking_method_ may be null if the lock is currently
	// unlocked, or if the lock is acquired by the system when the stack is empty.
	ArtMethod* locking_method_ GUARDED_BY(monitor_lock_);
	uint32_t locking_dex_pc_ GUARDED_BY(monitor_lock_);

	// The denser encoded version of this monitor as stored in the lock word.
	MonitorId monitor_id_;

	#ifdef __LP64__
	// Free list for monitor pool.
	Monitor* next_free_ GUARDED_BY(Locks::allocated_monitor_ids_lock_);
	#endif

	friend class MonitorInfo;
	friend class MonitorList;
	friend class MonitorPool;
	friend class mirror::Object;
	DISALLOW_COPY_AND_ASSIGN(Monitor);
	};

	class MonitorList {
	public:
	MonitorList();
	~MonitorList();

	void Add(Monitor* m) REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_list_lock_);

	void SweepMonitorList(IsMarkedVisitor* visitor)
	REQUIRES(!monitor_list_lock_) REQUIRES_SHARED(Locks::mutator_lock_);
	void DisallowNewMonitors() REQUIRES(!monitor_list_lock_);
	void AllowNewMonitors() REQUIRES(!monitor_list_lock_);
	void BroadcastForNewMonitors() REQUIRES(!monitor_list_lock_);
	// Returns how many monitors were deflated.
	size_t DeflateMonitors() REQUIRES(!monitor_list_lock_) REQUIRES(Locks::mutator_lock_);
	size_t Size() REQUIRES(!monitor_list_lock_);

	typedef std::list<Monitor, TrackingAllocator<Monitor, kAllocatorTagMonitorList>> Monitors;

	private:
	// During sweeping we may free an object and on a separate thread have an object created using
	// the newly freed memory. That object may then have its lock-word inflated and a monitor created.
	// If we allow new monitor registration during sweeping this monitor may be incorrectly freed as
	// the object wasn't marked when sweeping began.
	bool allow_new_monitors_ GUARDED_BY(monitor_list_lock_);
	Mutex monitor_list_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER;
	ConditionVariable monitor_add_condition_ GUARDED_BY(monitor_list_lock_);
	Monitors list_ GUARDED_BY(monitor_list_lock_);

	friend class Monitor;
	DISALLOW_COPY_AND_ASSIGN(MonitorList);
	};

	// Collects information about the current state of an object's monitor.
	// This is very unsafe, and must only be called when all threads are suspended.
	// For use only by the JDWP implementation.
	class MonitorInfo {
	public:
	MonitorInfo() : owner_(nullptr), entry_count_(0) {}
	MonitorInfo(const MonitorInfo&) = default;
	MonitorInfo& operator=(const MonitorInfo&) = default;
	explicit MonitorInfo(mirror::Object* o) REQUIRES(Locks::mutator_lock_);

	Thread* owner_;
	size_t entry_count_;
	std::vector<Thread*> waiters_;
	};

	} // namespace art

	#endif // ART_RUNTIME_MONITOR_H_