1 /* 2 * Copyright (C) 2008 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #ifndef ART_RUNTIME_MONITOR_H_ 18 #define ART_RUNTIME_MONITOR_H_ 19 20 #include <pthread.h> 21 #include <stdint.h> 22 #include <stdlib.h> 23 24 #include <iosfwd> 25 #include <list> 26 #include <vector> 27 28 #include "base/allocator.h" 29 #include "base/atomic.h" 30 #include "base/mutex.h" 31 #include "gc_root.h" 32 #include "lock_word.h" 33 #include "read_barrier_option.h" 34 #include "runtime_callbacks.h" 35 #include "thread_state.h" 36 37 namespace art { 38 39 class ArtMethod; 40 class IsMarkedVisitor; 41 class LockWord; 42 template<class T> class Handle; 43 class StackVisitor; 44 class Thread; 45 typedef uint32_t MonitorId; 46 47 namespace mirror { 48 class Object; 49 } // namespace mirror 50 51 enum class LockReason { 52 kForWait, 53 kForLock, 54 }; 55 56 class Monitor { 57 public: 58 // The default number of spins that are done before thread suspension is used to forcibly inflate 59 // a lock word. See Runtime::max_spins_before_thin_lock_inflation_. 60 constexpr static size_t kDefaultMaxSpinsBeforeThinLockInflation = 50; 61 62 ~Monitor(); 63 64 static void Init(uint32_t lock_profiling_threshold, uint32_t stack_dump_lock_profiling_threshold); 65 66 // Return the thread id of the lock owner or 0 when there is no owner. 67 static uint32_t GetLockOwnerThreadId(mirror::Object* obj) 68 NO_THREAD_SAFETY_ANALYSIS; // TODO: Reading lock owner without holding lock is racy. 69 70 // NO_THREAD_SAFETY_ANALYSIS for mon->Lock. 71 static mirror::Object* MonitorEnter(Thread* thread, mirror::Object* obj, bool trylock) 72 EXCLUSIVE_LOCK_FUNCTION(obj) 73 NO_THREAD_SAFETY_ANALYSIS 74 REQUIRES(!Roles::uninterruptible_) 75 REQUIRES_SHARED(Locks::mutator_lock_); 76 77 // NO_THREAD_SAFETY_ANALYSIS for mon->Unlock. 78 static bool MonitorExit(Thread* thread, mirror::Object* obj) 79 NO_THREAD_SAFETY_ANALYSIS 80 REQUIRES(!Roles::uninterruptible_) 81 REQUIRES_SHARED(Locks::mutator_lock_) 82 UNLOCK_FUNCTION(obj); 83 Notify(Thread * self,mirror::Object * obj)84 static void Notify(Thread* self, mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) { 85 DoNotify(self, obj, false); 86 } NotifyAll(Thread * self,mirror::Object * obj)87 static void NotifyAll(Thread* self, mirror::Object* obj) REQUIRES_SHARED(Locks::mutator_lock_) { 88 DoNotify(self, obj, true); 89 } 90 91 // Object.wait(). Also called for class init. 92 // NO_THREAD_SAFETY_ANALYSIS for mon->Wait. 93 static void Wait(Thread* self, mirror::Object* obj, int64_t ms, int32_t ns, 94 bool interruptShouldThrow, ThreadState why) 95 REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS; 96 97 static ThreadState FetchState(const Thread* thread, 98 /* out */ mirror::Object** monitor_object, 99 /* out */ uint32_t* lock_owner_tid) 100 REQUIRES(!Locks::thread_suspend_count_lock_) 101 REQUIRES_SHARED(Locks::mutator_lock_); 102 103 // Used to implement JDWP's ThreadReference.CurrentContendedMonitor. 104 static mirror::Object* GetContendedMonitor(Thread* thread) 105 REQUIRES_SHARED(Locks::mutator_lock_); 106 107 // Calls 'callback' once for each lock held in the single stack frame represented by 108 // the current state of 'stack_visitor'. 109 // The abort_on_failure flag allows to not die when the state of the runtime is unorderly. This 110 // is necessary when we have already aborted but want to dump the stack as much as we can. 111 static void VisitLocks(StackVisitor* stack_visitor, void (*callback)(mirror::Object*, void*), 112 void* callback_context, bool abort_on_failure = true) 113 REQUIRES_SHARED(Locks::mutator_lock_); 114 115 static bool IsValidLockWord(LockWord lock_word); 116 117 template<ReadBarrierOption kReadBarrierOption = kWithReadBarrier> GetObject()118 mirror::Object* GetObject() REQUIRES_SHARED(Locks::mutator_lock_) { 119 return obj_.Read<kReadBarrierOption>(); 120 } 121 122 void SetObject(mirror::Object* object); 123 GetOwner()124 Thread* GetOwner() const NO_THREAD_SAFETY_ANALYSIS { 125 return owner_; 126 } 127 128 int32_t GetHashCode(); 129 130 bool IsLocked() REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_lock_); 131 HasHashCode()132 bool HasHashCode() const { 133 return hash_code_.LoadRelaxed() != 0; 134 } 135 GetMonitorId()136 MonitorId GetMonitorId() const { 137 return monitor_id_; 138 } 139 140 // Inflate the lock on obj. May fail to inflate for spurious reasons, always re-check. 141 static void InflateThinLocked(Thread* self, Handle<mirror::Object> obj, LockWord lock_word, 142 uint32_t hash_code) REQUIRES_SHARED(Locks::mutator_lock_); 143 144 // Not exclusive because ImageWriter calls this during a Heap::VisitObjects() that 145 // does not allow a thread suspension in the middle. TODO: maybe make this exclusive. 146 // NO_THREAD_SAFETY_ANALYSIS for monitor->monitor_lock_. 147 static bool Deflate(Thread* self, mirror::Object* obj) 148 REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS; 149 150 #ifndef __LP64__ new(size_t size)151 void* operator new(size_t size) { 152 // Align Monitor* as per the monitor ID field size in the lock word. 153 void* result; 154 int error = posix_memalign(&result, LockWord::kMonitorIdAlignment, size); 155 CHECK_EQ(error, 0) << strerror(error); 156 return result; 157 } 158 delete(void * ptr)159 void operator delete(void* ptr) { 160 free(ptr); 161 } 162 #endif 163 164 private: 165 Monitor(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code) 166 REQUIRES_SHARED(Locks::mutator_lock_); 167 Monitor(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code, MonitorId id) 168 REQUIRES_SHARED(Locks::mutator_lock_); 169 170 // Install the monitor into its object, may fail if another thread installs a different monitor 171 // first. 172 bool Install(Thread* self) 173 REQUIRES(!monitor_lock_) 174 REQUIRES_SHARED(Locks::mutator_lock_); 175 176 // Links a thread into a monitor's wait set. The monitor lock must be held by the caller of this 177 // routine. 178 void AppendToWaitSet(Thread* thread) REQUIRES(monitor_lock_); 179 180 // Unlinks a thread from a monitor's wait set. The monitor lock must be held by the caller of 181 // this routine. 182 void RemoveFromWaitSet(Thread* thread) REQUIRES(monitor_lock_); 183 184 // Changes the shape of a monitor from thin to fat, preserving the internal lock state. The 185 // calling thread must own the lock or the owner must be suspended. There's a race with other 186 // threads inflating the lock, installing hash codes and spurious failures. The caller should 187 // re-read the lock word following the call. 188 static void Inflate(Thread* self, Thread* owner, mirror::Object* obj, int32_t hash_code) 189 REQUIRES_SHARED(Locks::mutator_lock_) 190 NO_THREAD_SAFETY_ANALYSIS; // For m->Install(self) 191 192 void LogContentionEvent(Thread* self, 193 uint32_t wait_ms, 194 uint32_t sample_percent, 195 ArtMethod* owner_method, 196 uint32_t owner_dex_pc) 197 REQUIRES_SHARED(Locks::mutator_lock_); 198 199 static void FailedUnlock(mirror::Object* obj, 200 uint32_t expected_owner_thread_id, 201 uint32_t found_owner_thread_id, 202 Monitor* mon) 203 REQUIRES(!Locks::thread_list_lock_, 204 !monitor_lock_) 205 REQUIRES_SHARED(Locks::mutator_lock_); 206 207 // Try to lock without blocking, returns true if we acquired the lock. 208 bool TryLock(Thread* self) 209 REQUIRES(!monitor_lock_) 210 REQUIRES_SHARED(Locks::mutator_lock_); 211 // Variant for already holding the monitor lock. 212 bool TryLockLocked(Thread* self) 213 REQUIRES(monitor_lock_) 214 REQUIRES_SHARED(Locks::mutator_lock_); 215 216 template<LockReason reason = LockReason::kForLock> 217 void Lock(Thread* self) 218 REQUIRES(!monitor_lock_) 219 REQUIRES_SHARED(Locks::mutator_lock_); 220 221 bool Unlock(Thread* thread) 222 REQUIRES(!monitor_lock_) 223 REQUIRES_SHARED(Locks::mutator_lock_); 224 225 static void DoNotify(Thread* self, mirror::Object* obj, bool notify_all) 226 REQUIRES_SHARED(Locks::mutator_lock_) NO_THREAD_SAFETY_ANALYSIS; // For mon->Notify. 227 228 void Notify(Thread* self) 229 REQUIRES(!monitor_lock_) 230 REQUIRES_SHARED(Locks::mutator_lock_); 231 232 void NotifyAll(Thread* self) 233 REQUIRES(!monitor_lock_) 234 REQUIRES_SHARED(Locks::mutator_lock_); 235 236 static std::string PrettyContentionInfo(const std::string& owner_name, 237 pid_t owner_tid, 238 ArtMethod* owners_method, 239 uint32_t owners_dex_pc, 240 size_t num_waiters) 241 REQUIRES_SHARED(Locks::mutator_lock_); 242 243 // Wait on a monitor until timeout, interrupt, or notification. Used for Object.wait() and 244 // (somewhat indirectly) Thread.sleep() and Thread.join(). 245 // 246 // If another thread calls Thread.interrupt(), we throw InterruptedException and return 247 // immediately if one of the following are true: 248 // - blocked in wait(), wait(long), or wait(long, int) methods of Object 249 // - blocked in join(), join(long), or join(long, int) methods of Thread 250 // - blocked in sleep(long), or sleep(long, int) methods of Thread 251 // Otherwise, we set the "interrupted" flag. 252 // 253 // Checks to make sure that "ns" is in the range 0-999999 (i.e. fractions of a millisecond) and 254 // throws the appropriate exception if it isn't. 255 // 256 // The spec allows "spurious wakeups", and recommends that all code using Object.wait() do so in 257 // a loop. This appears to derive from concerns about pthread_cond_wait() on multiprocessor 258 // systems. Some commentary on the web casts doubt on whether these can/should occur. 259 // 260 // Since we're allowed to wake up "early", we clamp extremely long durations to return at the end 261 // of the 32-bit time epoch. 262 void Wait(Thread* self, int64_t msec, int32_t nsec, bool interruptShouldThrow, ThreadState why) 263 REQUIRES(!monitor_lock_) 264 REQUIRES_SHARED(Locks::mutator_lock_); 265 266 // Translates the provided method and pc into its declaring class' source file and line number. 267 static void TranslateLocation(ArtMethod* method, uint32_t pc, 268 const char** source_file, 269 int32_t* line_number) 270 REQUIRES_SHARED(Locks::mutator_lock_); 271 272 uint32_t GetOwnerThreadId() REQUIRES(!monitor_lock_); 273 274 // Support for systrace output of monitor operations. 275 ALWAYS_INLINE static void AtraceMonitorLock(Thread* self, 276 mirror::Object* obj, 277 bool is_wait) 278 REQUIRES_SHARED(Locks::mutator_lock_); 279 static void AtraceMonitorLockImpl(Thread* self, 280 mirror::Object* obj, 281 bool is_wait) 282 REQUIRES_SHARED(Locks::mutator_lock_); 283 ALWAYS_INLINE static void AtraceMonitorUnlock(); 284 285 static uint32_t lock_profiling_threshold_; 286 static uint32_t stack_dump_lock_profiling_threshold_; 287 288 Mutex monitor_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER; 289 290 ConditionVariable monitor_contenders_ GUARDED_BY(monitor_lock_); 291 292 // Number of people waiting on the condition. 293 size_t num_waiters_ GUARDED_BY(monitor_lock_); 294 295 // Which thread currently owns the lock? 296 Thread* volatile owner_ GUARDED_BY(monitor_lock_); 297 298 // Owner's recursive lock depth. 299 int lock_count_ GUARDED_BY(monitor_lock_); 300 301 // What object are we part of. This is a weak root. Do not access 302 // this directly, use GetObject() to read it so it will be guarded 303 // by a read barrier. 304 GcRoot<mirror::Object> obj_; 305 306 // Threads currently waiting on this monitor. 307 Thread* wait_set_ GUARDED_BY(monitor_lock_); 308 309 // Stored object hash code, generated lazily by GetHashCode. 310 AtomicInteger hash_code_; 311 312 // Method and dex pc where the lock owner acquired the lock, used when lock 313 // sampling is enabled. locking_method_ may be null if the lock is currently 314 // unlocked, or if the lock is acquired by the system when the stack is empty. 315 ArtMethod* locking_method_ GUARDED_BY(monitor_lock_); 316 uint32_t locking_dex_pc_ GUARDED_BY(monitor_lock_); 317 318 // The denser encoded version of this monitor as stored in the lock word. 319 MonitorId monitor_id_; 320 321 #ifdef __LP64__ 322 // Free list for monitor pool. 323 Monitor* next_free_ GUARDED_BY(Locks::allocated_monitor_ids_lock_); 324 #endif 325 326 friend class MonitorInfo; 327 friend class MonitorList; 328 friend class MonitorPool; 329 friend class mirror::Object; 330 DISALLOW_COPY_AND_ASSIGN(Monitor); 331 }; 332 333 class MonitorList { 334 public: 335 MonitorList(); 336 ~MonitorList(); 337 338 void Add(Monitor* m) REQUIRES_SHARED(Locks::mutator_lock_) REQUIRES(!monitor_list_lock_); 339 340 void SweepMonitorList(IsMarkedVisitor* visitor) 341 REQUIRES(!monitor_list_lock_) REQUIRES_SHARED(Locks::mutator_lock_); 342 void DisallowNewMonitors() REQUIRES(!monitor_list_lock_); 343 void AllowNewMonitors() REQUIRES(!monitor_list_lock_); 344 void BroadcastForNewMonitors() REQUIRES(!monitor_list_lock_); 345 // Returns how many monitors were deflated. 346 size_t DeflateMonitors() REQUIRES(!monitor_list_lock_) REQUIRES(Locks::mutator_lock_); 347 size_t Size() REQUIRES(!monitor_list_lock_); 348 349 typedef std::list<Monitor*, TrackingAllocator<Monitor*, kAllocatorTagMonitorList>> Monitors; 350 351 private: 352 // During sweeping we may free an object and on a separate thread have an object created using 353 // the newly freed memory. That object may then have its lock-word inflated and a monitor created. 354 // If we allow new monitor registration during sweeping this monitor may be incorrectly freed as 355 // the object wasn't marked when sweeping began. 356 bool allow_new_monitors_ GUARDED_BY(monitor_list_lock_); 357 Mutex monitor_list_lock_ DEFAULT_MUTEX_ACQUIRED_AFTER; 358 ConditionVariable monitor_add_condition_ GUARDED_BY(monitor_list_lock_); 359 Monitors list_ GUARDED_BY(monitor_list_lock_); 360 361 friend class Monitor; 362 DISALLOW_COPY_AND_ASSIGN(MonitorList); 363 }; 364 365 // Collects information about the current state of an object's monitor. 366 // This is very unsafe, and must only be called when all threads are suspended. 367 // For use only by the JDWP implementation. 368 class MonitorInfo { 369 public: MonitorInfo()370 MonitorInfo() : owner_(nullptr), entry_count_(0) {} 371 MonitorInfo(const MonitorInfo&) = default; 372 MonitorInfo& operator=(const MonitorInfo&) = default; 373 explicit MonitorInfo(mirror::Object* o) REQUIRES(Locks::mutator_lock_); 374 375 Thread* owner_; 376 size_t entry_count_; 377 std::vector<Thread*> waiters_; 378 }; 379 380 } // namespace art 381 382 #endif // ART_RUNTIME_MONITOR_H_ 383