/* * 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 #include #include #include #include #include #include #include "base/allocator.h" #include "base/atomic.h" #include "base/mutex.h" #include "gc_root.h" #include "lock_word.h" #include "obj_ptr.h" #include "read_barrier_option.h" #include "runtime_callbacks.h" #include "thread_state.h" namespace art { class ArtMethod; class IsMarkedVisitor; class LockWord; template 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; static constexpr int kDefaultMonitorTimeoutMs = 500; static constexpr int kMonitorTimeoutMinMs = 200; static constexpr int kMonitorTimeoutMaxMs = 1000; // 1 second ~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(ObjPtr obj) NO_THREAD_SAFETY_ANALYSIS; // TODO: Reading lock owner without holding lock is racy. // NO_THREAD_SAFETY_ANALYSIS for mon->Lock. static ObjPtr MonitorEnter(Thread* thread, ObjPtr obj, bool trylock) EXCLUSIVE_LOCK_FUNCTION(obj.Ptr()) NO_THREAD_SAFETY_ANALYSIS REQUIRES(!Roles::uninterruptible_) REQUIRES_SHARED(Locks::mutator_lock_); // NO_THREAD_SAFETY_ANALYSIS for mon->Unlock. static bool MonitorExit(Thread* thread, ObjPtr obj) NO_THREAD_SAFETY_ANALYSIS REQUIRES(!Roles::uninterruptible_) REQUIRES_SHARED(Locks::mutator_lock_) UNLOCK_FUNCTION(obj.Ptr()); static void Notify(Thread* self, ObjPtr obj) REQUIRES_SHARED(Locks::mutator_lock_) { DoNotify(self, obj, false); } static void NotifyAll(Thread* self, ObjPtr 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, ObjPtr 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 */ ObjPtr* 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 ObjPtr 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)(ObjPtr, void*), void* callback_context, bool abort_on_failure = true) REQUIRES_SHARED(Locks::mutator_lock_); static bool IsValidLockWord(LockWord lock_word); template ObjPtr GetObject() REQUIRES_SHARED(Locks::mutator_lock_); void SetObject(ObjPtr object); // Provides no memory ordering guarantees. Thread* GetOwner() const { return owner_.load(std::memory_order_relaxed); } int32_t GetHashCode(); // Is the monitor currently locked? Debug only, provides no memory ordering guarantees. bool IsLocked() REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_lock_); bool HasHashCode() const { return hash_code_.load(std::memory_order_relaxed) != 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 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, ObjPtr 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, ObjPtr obj, int32_t hash_code) REQUIRES_SHARED(Locks::mutator_lock_); Monitor(Thread* self, Thread* owner, ObjPtr 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. Monitor remains in the same logical state as before, i.e. held the same # of times. 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_); // Release the monitor lock and signal a waiting thread that has been notified and now needs the // lock. Assumes the monitor lock is held exactly once, and the owner_ field has been reset to // null. Caller may be suspended (Wait) or runnable (MonitorExit). void SignalWaiterAndReleaseMonitorLock(Thread* self) RELEASE(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, ObjPtr 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(ObjPtr obj, uint32_t expected_owner_thread_id, uint32_t found_owner_thread_id, Monitor* mon) REQUIRES(!Locks::thread_list_lock_) REQUIRES_SHARED(Locks::mutator_lock_); // Try to lock without blocking, returns true if we acquired the lock. // If spin is true, then we spin for a short period before failing. bool TryLock(Thread* self, bool spin = false) TRY_ACQUIRE(true, monitor_lock_) REQUIRES_SHARED(Locks::mutator_lock_); template void Lock(Thread* self) ACQUIRE(monitor_lock_) REQUIRES_SHARED(Locks::mutator_lock_); bool Unlock(Thread* thread) RELEASE(monitor_lock_) REQUIRES_SHARED(Locks::mutator_lock_); static void DoNotify(Thread* self, ObjPtr 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_); // Provides no memory ordering guarantees. uint32_t GetOwnerThreadId() REQUIRES(!monitor_lock_); // Set locking_method_ and locking_dex_pc_ corresponding to owner's current stack. // owner is either self or suspended. void SetLockingMethod(Thread* owner) REQUIRES(monitor_lock_) REQUIRES_SHARED(Locks::mutator_lock_); // The same, but without checking for a proxy method. Currently requires owner == self. void SetLockingMethodNoProxy(Thread* owner) REQUIRES(monitor_lock_) REQUIRES_SHARED(Locks::mutator_lock_); // Support for systrace output of monitor operations. ALWAYS_INLINE static void AtraceMonitorLock(Thread* self, ObjPtr obj, bool is_wait) REQUIRES_SHARED(Locks::mutator_lock_); static void AtraceMonitorLockImpl(Thread* self, ObjPtr 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_; static bool capture_method_eagerly_; // Holding the monitor N times is represented by holding monitor_lock_ N times. Mutex monitor_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER; // Pretend to unlock monitor lock. void FakeUnlockMonitorLock() RELEASE(monitor_lock_) NO_THREAD_SAFETY_ANALYSIS {} // Number of threads either waiting on the condition or waiting on a contended // monitor acquisition. Prevents deflation. std::atomic num_waiters_; // Which thread currently owns the lock? monitor_lock_ only keeps the tid. // Only set while holding monitor_lock_. Non-locking readers only use it to // compare to self or for debugging. std::atomic owner_; // Owner's recursive lock depth. Owner_ non-null, and lock_count_ == 0 ==> held once. unsigned int lock_count_ GUARDED_BY(monitor_lock_); // Owner's recursive lock depth is given by monitor_lock_.GetDepth(). // 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 obj_; // Threads currently waiting on this monitor. Thread* wait_set_ GUARDED_BY(monitor_lock_); // Threads that were waiting on this monitor, but are now contending on it. Thread* wake_set_ GUARDED_BY(monitor_lock_); // Stored object hash code, generated lazily by GetHashCode. AtomicInteger hash_code_; // Data structure used to remember the method and dex pc of a recent holder of the // lock. Used for tracing and contention reporting. Setting these is expensive, since it // involves a partial stack walk. We set them only as follows, to minimize the cost: // - If tracing is enabled, they are needed immediately when we first notice contention, so we // set them unconditionally when a monitor is acquired. // - If contention reporting is enabled, we use the lock_owner_request_ field to have the // contending thread request them. The current owner then sets them when releasing the monitor, // making them available when the contending thread acquires the monitor. // - If tracing and contention reporting are enabled, we do both. This usually prevents us from // switching between reporting the end and beginning of critical sections for contention logging // when tracing is enabled. We expect that tracing overhead is normally much higher than for // contention logging, so the added cost should be small. It also minimizes glitches when // enabling and disabling traces. // We're tolerant of missing information. E.g. when tracing is initially turned on, we may // not have the lock holder information if the holder acquired the lock with tracing off. // // We make this data unconditionally atomic; for contention logging all accesses are in fact // protected by the monitor, but for tracing, reads are not. Writes are always // protected by the monitor. // // The fields are always accessed without memory ordering. We store a checksum, and reread if // the checksum doesn't correspond to the values. This results in values that are correct with // very high probability, but not certainty. // // If we need lock_owner information for a certain thread for contenion logging, we store its // tid in lock_owner_request_. To satisfy the request, we store lock_owner_tid_, // lock_owner_method_, and lock_owner_dex_pc_ and the corresponding checksum while holding the // monitor. // // At all times, either lock_owner_ is zero, the checksum is valid, or a thread is actively // in the process of establishing one of those states. Only one thread at a time can be actively // establishing such a state, since writes are protected by the monitor. std::atomic lock_owner_; // *lock_owner_ may no longer exist! std::atomic lock_owner_method_; std::atomic lock_owner_dex_pc_; std::atomic lock_owner_sum_; // Request lock owner save method and dex_pc. Written asynchronously. std::atomic lock_owner_request_; // Compute method, dex pc, and tid "checksum". uintptr_t LockOwnerInfoChecksum(ArtMethod* m, uint32_t dex_pc, Thread* t); // Set owning method, dex pc, and tid. owner_ field is set and points to current thread. void SetLockOwnerInfo(ArtMethod* method, uint32_t dex_pc, Thread* t) REQUIRES(monitor_lock_); // Get owning method and dex pc for the given thread, if available. void GetLockOwnerInfo(/*out*/ArtMethod** method, /*out*/uint32_t* dex_pc, Thread* t); // Do the same, while holding the monitor. There are no concurrent updates. void GetLockOwnerInfoLocked(/*out*/ArtMethod** method, /*out*/uint32_t* dex_pc, uint32_t thread_id) REQUIRES(monitor_lock_); // We never clear lock_owner method and dex pc. Since it often reflects // ownership when we last detected contention, it may be inconsistent with owner_ // and not 100% reliable. For lock contention monitoring, in the absence of tracing, // there is a small risk that the current owner may finish before noticing the request, // or the information will be overwritten by another intervening request and monitor // release, so it's also not 100% reliable. But if we report information at all, it // should generally (modulo accidental checksum matches) pertain to to an acquisition of the // right monitor by the right thread, so it's extremely unlikely to be seriously misleading. // Since we track threads by a pointer to the Thread structure, there is a small chance we may // confuse threads allocated at the same exact address, if a contending thread dies before // we inquire about it. // Check for and act on a pending lock_owner_request_ void CheckLockOwnerRequest(Thread* self) REQUIRES(monitor_lock_) REQUIRES_SHARED(Locks::mutator_lock_); void MaybeEnableTimeout() REQUIRES(Locks::mutator_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> 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(ObjPtr o) REQUIRES(Locks::mutator_lock_); Thread* owner_; size_t entry_count_; std::vector waiters_; }; } // namespace art #endif // ART_RUNTIME_MONITOR_H_