1 /*
2  * Copyright (C) 2011 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_THREAD_LIST_H_
18 #define ART_RUNTIME_THREAD_LIST_H_
19 
20 #include "barrier.h"
21 #include "base/histogram.h"
22 #include "base/mutex.h"
23 #include "base/time_utils.h"
24 #include "base/value_object.h"
25 #include "jni.h"
26 #include "suspend_reason.h"
27 
28 #include <bitset>
29 #include <list>
30 #include <vector>
31 
32 namespace art {
33 namespace gc {
34 namespace collector {
35 class GarbageCollector;
36 }  // namespace collector
37 class GcPauseListener;
38 }  // namespace gc
39 class Closure;
40 class RootVisitor;
41 class Thread;
42 class TimingLogger;
43 enum VisitRootFlags : uint8_t;
44 
45 class ThreadList {
46  public:
47   static constexpr uint32_t kMaxThreadId = 0xFFFF;
48   static constexpr uint32_t kInvalidThreadId = 0;
49   static constexpr uint32_t kMainThreadId = 1;
50   static constexpr uint64_t kDefaultThreadSuspendTimeout = MsToNs(kIsDebugBuild ? 50000 : 10000);
51 
52   explicit ThreadList(uint64_t thread_suspend_timeout_ns);
53   ~ThreadList();
54 
55   void ShutDown();
56 
57   void DumpForSigQuit(std::ostream& os)
58       REQUIRES(!Locks::thread_list_lock_, !Locks::mutator_lock_);
59   // For thread suspend timeout dumps.
60   void Dump(std::ostream& os, bool dump_native_stack = true)
61       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
62   pid_t GetLockOwner();  // For SignalCatcher.
63 
64   // Thread suspension support.
65   void ResumeAll()
66       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_)
67       UNLOCK_FUNCTION(Locks::mutator_lock_);
68   bool Resume(Thread* thread, SuspendReason reason = SuspendReason::kInternal)
69       REQUIRES(!Locks::thread_suspend_count_lock_) WARN_UNUSED;
70 
71   // Suspends all threads and gets exclusive access to the mutator lock.
72   // If long_suspend is true, then other threads who try to suspend will never timeout.
73   // long_suspend is currenly used for hprof since large heaps take a long time.
74   void SuspendAll(const char* cause, bool long_suspend = false)
75       EXCLUSIVE_LOCK_FUNCTION(Locks::mutator_lock_)
76       REQUIRES(!Locks::thread_list_lock_,
77                !Locks::thread_suspend_count_lock_,
78                !Locks::mutator_lock_);
79 
80   // Suspend a thread using a peer, typically used by the debugger. Returns the thread on success,
81   // else null. The peer is used to identify the thread to avoid races with the thread terminating.
82   // If the thread should be suspended then value of request_suspension should be true otherwise
83   // the routine will wait for a previous suspend request. If the suspension times out then *timeout
84   // is set to true.
85   Thread* SuspendThreadByPeer(jobject peer,
86                               bool request_suspension,
87                               SuspendReason reason,
88                               bool* timed_out)
89       REQUIRES(!Locks::mutator_lock_,
90                !Locks::thread_list_lock_,
91                !Locks::thread_suspend_count_lock_);
92 
93   // Suspend a thread using its thread id, typically used by lock/monitor inflation. Returns the
94   // thread on success else null. The thread id is used to identify the thread to avoid races with
95   // the thread terminating. Note that as thread ids are recycled this may not suspend the expected
96   // thread, that may be terminating. If the suspension times out then *timeout is set to true.
97   Thread* SuspendThreadByThreadId(uint32_t thread_id, SuspendReason reason, bool* timed_out)
98       REQUIRES(!Locks::mutator_lock_,
99                !Locks::thread_list_lock_,
100                !Locks::thread_suspend_count_lock_);
101 
102   // Find an existing thread (or self) by its thread id (not tid).
103   Thread* FindThreadByThreadId(uint32_t thread_id) REQUIRES(Locks::thread_list_lock_);
104 
105   // Run a checkpoint on threads, running threads are not suspended but run the checkpoint inside
106   // of the suspend check. Returns how many checkpoints that are expected to run, including for
107   // already suspended threads for b/24191051. Run the callback, if non-null, inside the
108   // thread_list_lock critical section after determining the runnable/suspended states of the
109   // threads.
110   size_t RunCheckpoint(Closure* checkpoint_function, Closure* callback = nullptr)
111       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
112 
113   // Run an empty checkpoint on threads. Wait until threads pass the next suspend point or are
114   // suspended. This is used to ensure that the threads finish or aren't in the middle of an
115   // in-flight mutator heap access (eg. a read barrier.) Runnable threads will respond by
116   // decrementing the empty checkpoint barrier count. This works even when the weak ref access is
117   // disabled. Only one concurrent use is currently supported.
118   void RunEmptyCheckpoint()
119       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
120 
121   // Flip thread roots from from-space refs to to-space refs. Used by
122   // the concurrent copying collector.
123   size_t FlipThreadRoots(Closure* thread_flip_visitor,
124                          Closure* flip_callback,
125                          gc::collector::GarbageCollector* collector,
126                          gc::GcPauseListener* pause_listener)
127       REQUIRES(!Locks::mutator_lock_,
128                !Locks::thread_list_lock_,
129                !Locks::thread_suspend_count_lock_);
130 
131   // Suspends all threads
132   void SuspendAllForDebugger()
133       REQUIRES(!Locks::mutator_lock_,
134                !Locks::thread_list_lock_,
135                !Locks::thread_suspend_count_lock_);
136 
137   void SuspendSelfForDebugger()
138       REQUIRES(!Locks::thread_suspend_count_lock_);
139 
140   // Resume all threads
141   void ResumeAllForDebugger()
142       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
143 
144   void UndoDebuggerSuspensions()
145       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
146 
147   // Iterates over all the threads.
148   void ForEach(void (*callback)(Thread*, void*), void* context)
149       REQUIRES(Locks::thread_list_lock_);
150 
151   // Add/remove current thread from list.
152   void Register(Thread* self)
153       REQUIRES(Locks::runtime_shutdown_lock_)
154       REQUIRES(!Locks::mutator_lock_,
155                !Locks::thread_list_lock_,
156                !Locks::thread_suspend_count_lock_);
157   void Unregister(Thread* self)
158       REQUIRES(!Locks::mutator_lock_,
159                !Locks::thread_list_lock_,
160                !Locks::thread_suspend_count_lock_);
161 
162   void VisitRoots(RootVisitor* visitor, VisitRootFlags flags) const
163       REQUIRES_SHARED(Locks::mutator_lock_);
164 
165   void VisitRootsForSuspendedThreads(RootVisitor* visitor)
166       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_)
167       REQUIRES_SHARED(Locks::mutator_lock_);
168 
169   // Return a copy of the thread list.
GetList()170   std::list<Thread*> GetList() REQUIRES(Locks::thread_list_lock_) {
171     return list_;
172   }
173 
174   void DumpNativeStacks(std::ostream& os)
175       REQUIRES(!Locks::thread_list_lock_);
176 
EmptyCheckpointBarrier()177   Barrier* EmptyCheckpointBarrier() {
178     return empty_checkpoint_barrier_.get();
179   }
180 
181  private:
182   uint32_t AllocThreadId(Thread* self);
183   void ReleaseThreadId(Thread* self, uint32_t id) REQUIRES(!Locks::allocated_thread_ids_lock_);
184 
185   bool Contains(Thread* thread) REQUIRES(Locks::thread_list_lock_);
186   bool Contains(pid_t tid) REQUIRES(Locks::thread_list_lock_);
187   size_t RunCheckpoint(Closure* checkpoint_function, bool includeSuspended)
188       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
189 
190   void DumpUnattachedThreads(std::ostream& os, bool dump_native_stack)
191       REQUIRES(!Locks::thread_list_lock_);
192 
193   void SuspendAllDaemonThreadsForShutdown()
194       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
195   void WaitForOtherNonDaemonThreadsToExit()
196       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
197 
198   void SuspendAllInternal(Thread* self,
199                           Thread* ignore1,
200                           Thread* ignore2 = nullptr,
201                           SuspendReason reason = SuspendReason::kInternal)
202       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
203 
204   void AssertThreadsAreSuspended(Thread* self, Thread* ignore1, Thread* ignore2 = nullptr)
205       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_);
206 
207   std::bitset<kMaxThreadId> allocated_ids_ GUARDED_BY(Locks::allocated_thread_ids_lock_);
208 
209   // The actual list of all threads.
210   std::list<Thread*> list_ GUARDED_BY(Locks::thread_list_lock_);
211 
212   // Ongoing suspend all requests, used to ensure threads added to list_ respect SuspendAll.
213   int suspend_all_count_ GUARDED_BY(Locks::thread_suspend_count_lock_);
214   int debug_suspend_all_count_ GUARDED_BY(Locks::thread_suspend_count_lock_);
215 
216   // Number of threads unregistering, ~ThreadList blocks until this hits 0.
217   int unregistering_count_ GUARDED_BY(Locks::thread_list_lock_);
218 
219   // Thread suspend time histogram. Only modified when all the threads are suspended, so guarding
220   // by mutator lock ensures no thread can read when another thread is modifying it.
221   Histogram<uint64_t> suspend_all_historam_ GUARDED_BY(Locks::mutator_lock_);
222 
223   // Whether or not the current thread suspension is long.
224   bool long_suspend_;
225 
226   // Whether the shutdown function has been called. This is checked in the destructor. It is an
227   // error to destroy a ThreadList instance without first calling ShutDown().
228   bool shut_down_;
229 
230   // Thread suspension timeout in nanoseconds.
231   const uint64_t thread_suspend_timeout_ns_;
232 
233   std::unique_ptr<Barrier> empty_checkpoint_barrier_;
234 
235   friend class Thread;
236 
237   DISALLOW_COPY_AND_ASSIGN(ThreadList);
238 };
239 
240 // Helper for suspending all threads and getting exclusive access to the mutator lock.
241 class ScopedSuspendAll : public ValueObject {
242  public:
243   explicit ScopedSuspendAll(const char* cause, bool long_suspend = false)
244      EXCLUSIVE_LOCK_FUNCTION(Locks::mutator_lock_)
245      REQUIRES(!Locks::thread_list_lock_,
246               !Locks::thread_suspend_count_lock_,
247               !Locks::mutator_lock_);
248   // No REQUIRES(mutator_lock_) since the unlock function already asserts this.
249   ~ScopedSuspendAll()
250       REQUIRES(!Locks::thread_list_lock_, !Locks::thread_suspend_count_lock_)
251       UNLOCK_FUNCTION(Locks::mutator_lock_);
252 };
253 
254 }  // namespace art
255 
256 #endif  // ART_RUNTIME_THREAD_LIST_H_
257