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