1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_RUNTIME_OBJECTMONITOR_HPP
26 #define SHARE_RUNTIME_OBJECTMONITOR_HPP
27
28 #include "memory/allocation.hpp"
29 #include "memory/padded.hpp"
30 #include "oops/markWord.hpp"
31 #include "runtime/os.hpp"
32 #include "runtime/park.hpp"
33 #include "runtime/perfData.hpp"
34
35 class ObjectMonitor;
36
37 // ObjectWaiter serves as a "proxy" or surrogate thread.
38 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
39 // ParkEvent instead. Beware, however, that the JVMTI code
40 // knows about ObjectWaiters, so we'll have to reconcile that code.
41 // See next_waiter(), first_waiter(), etc.
42
43 class ObjectWaiter : public StackObj {
44 public:
45 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
46 enum Sorted { PREPEND, APPEND, SORTED };
47 ObjectWaiter* volatile _next;
48 ObjectWaiter* volatile _prev;
49 Thread* _thread;
50 jlong _notifier_tid;
51 ParkEvent * _event;
52 volatile int _notified;
53 volatile TStates TState;
54 Sorted _Sorted; // List placement disposition
55 bool _active; // Contention monitoring is enabled
56 public:
57 ObjectWaiter(Thread* thread);
58
59 void wait_reenter_begin(ObjectMonitor *mon);
60 void wait_reenter_end(ObjectMonitor *mon);
61 };
62
63 // The ObjectMonitor class implements the heavyweight version of a
64 // JavaMonitor. The lightweight BasicLock/stack lock version has been
65 // inflated into an ObjectMonitor. This inflation is typically due to
66 // contention or use of Object.wait().
67 //
68 // WARNING: This is a very sensitive and fragile class. DO NOT make any
69 // changes unless you are fully aware of the underlying semantics.
70 //
71 // Class JvmtiRawMonitor currently inherits from ObjectMonitor so
72 // changes in this class must be careful to not break JvmtiRawMonitor.
73 // These two subsystems should be separated.
74 //
75 // ObjectMonitor Layout Overview/Highlights/Restrictions:
76 //
77 // - The _header field must be at offset 0 because the displaced header
78 // from markWord is stored there. We do not want markWord.hpp to include
79 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
80 // means that ObjectMonitor cannot inherit from any other class nor can
81 // it use any virtual member functions. This restriction is critical to
82 // the proper functioning of the VM.
83 // - The _header and _owner fields should be separated by enough space
84 // to avoid false sharing due to parallel access by different threads.
85 // This is an advisory recommendation.
86 // - The general layout of the fields in ObjectMonitor is:
87 // _header
88 // <lightly_used_fields>
89 // <optional padding>
90 // _owner
91 // <remaining_fields>
92 // - The VM assumes write ordering and machine word alignment with
93 // respect to the _owner field and the <remaining_fields> that can
94 // be read in parallel by other threads.
95 // - Generally fields that are accessed closely together in time should
96 // be placed proximally in space to promote data cache locality. That
97 // is, temporal locality should condition spatial locality.
98 // - We have to balance avoiding false sharing with excessive invalidation
99 // from coherence traffic. As such, we try to cluster fields that tend
100 // to be _written_ at approximately the same time onto the same data
101 // cache line.
102 // - We also have to balance the natural tension between minimizing
103 // single threaded capacity misses with excessive multi-threaded
104 // coherency misses. There is no single optimal layout for both
105 // single-threaded and multi-threaded environments.
106 //
107 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
108 // enforced.
109 // - Adjacent ObjectMonitors should be separated by enough space to avoid
110 // false sharing. This is handled by the ObjectMonitor allocation code
111 // in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
112 //
113 // Futures notes:
114 // - Separating _owner from the <remaining_fields> by enough space to
115 // avoid false sharing might be profitable. Given
116 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
117 // we know that the CAS in monitorenter will invalidate the line
118 // underlying _owner. We want to avoid an L1 data cache miss on that
119 // same line for monitorexit. Putting these <remaining_fields>:
120 // _recursions, _EntryList, _cxq, and _succ, all of which may be
121 // fetched in the inflated unlock path, on a different cache line
122 // would make them immune to CAS-based invalidation from the _owner
123 // field.
124 //
125 // - The _recursions field should be of type int, or int32_t but not
126 // intptr_t. There's no reason to use a 64-bit type for this field
127 // in a 64-bit JVM.
128
129 class ObjectMonitor {
130 public:
131 enum {
132 OM_OK, // no error
133 OM_SYSTEM_ERROR, // operating system error
134 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
135 OM_INTERRUPTED, // Thread.interrupt()
136 OM_TIMED_OUT // Object.wait() timed out
137 };
138
139 private:
140 friend class ObjectSynchronizer;
141 friend class ObjectWaiter;
142 friend class VMStructs;
143 JVMCI_ONLY(friend class JVMCIVMStructs;)
144
145 // The sync code expects the header field to be at offset zero (0).
146 // Enforced by the assert() in header_addr().
147 volatile markWord _header; // displaced object header word - mark
148 void* volatile _object; // backward object pointer - strong root
149 public:
150 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage
151 private:
152 // Separate _header and _owner on different cache lines since both can
153 // have busy multi-threaded access. _header and _object are set at
154 // initial inflation and _object doesn't change until deflation so
155 // _object is a good choice to share the cache line with _header.
156 // _next_om shares _header's cache line for pre-monitor list historical
157 // reasons. _next_om only changes if the next ObjectMonitor is deflated.
158 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
159 sizeof(volatile markWord) + sizeof(void* volatile) +
160 sizeof(ObjectMonitor *));
161 protected: // protected for JvmtiRawMonitor
162 void* volatile _owner; // pointer to owning thread OR BasicLock
163 private:
164 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
165 protected: // protected for JvmtiRawMonitor
166 volatile intptr_t _recursions; // recursion count, 0 for first entry
167 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry.
168 // The list is actually composed of WaitNodes,
169 // acting as proxies for Threads.
170 private:
171 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry.
172 Thread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
173 Thread* volatile _Responsible;
174
175 volatile int _Spinner; // for exit->spinner handoff optimization
176 volatile int _SpinDuration;
177
178 volatile jint _contentions; // Number of active contentions in enter(). It is used by is_busy()
179 // along with other fields to determine if an ObjectMonitor can be
180 // deflated. See ObjectSynchronizer::deflate_monitor().
181 protected:
182 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor
183 volatile jint _waiters; // number of waiting threads
184 private:
185 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
186
187 public:
188 static void Initialize();
189
190 // Only perform a PerfData operation if the PerfData object has been
191 // allocated and if the PerfDataManager has not freed the PerfData
192 // objects which can happen at normal VM shutdown.
193 //
194 #define OM_PERFDATA_OP(f, op_str) \
195 do { \
196 if (ObjectMonitor::_sync_ ## f != NULL && \
197 PerfDataManager::has_PerfData()) { \
198 ObjectMonitor::_sync_ ## f->op_str; \
199 } \
200 } while (0)
201
202 static PerfCounter * _sync_ContendedLockAttempts;
203 static PerfCounter * _sync_FutileWakeups;
204 static PerfCounter * _sync_Parks;
205 static PerfCounter * _sync_Notifications;
206 static PerfCounter * _sync_Inflations;
207 static PerfCounter * _sync_Deflations;
208 static PerfLongVariable * _sync_MonExtant;
209
210 static int Knob_SpinLimit;
211
212 void* operator new (size_t size) throw();
213 void* operator new[] (size_t size) throw();
214 void operator delete(void* p);
215 void operator delete[] (void* p);
216
217 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
218 // ByteSize would also be an appropriate type.
219 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); }
220 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); }
221 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); }
222 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
223 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); }
224 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); }
225 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
226
227 // ObjectMonitor references can be ORed with markWord::monitor_value
228 // as part of the ObjectMonitor tagging mechanism. When we combine an
229 // ObjectMonitor reference with an offset, we need to remove the tag
230 // value in order to generate the proper address.
231 //
232 // We can either adjust the ObjectMonitor reference and then add the
233 // offset or we can adjust the offset that is added to the ObjectMonitor
234 // reference. The latter avoids an AGI (Address Generation Interlock)
235 // stall so the helper macro adjusts the offset value that is returned
236 // to the ObjectMonitor reference manipulation code:
237 //
238 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
239 ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value)
240
241 markWord header() const;
242 volatile markWord* header_addr();
243 void set_header(markWord hdr);
244
245 intptr_t is_busy() const {
246 // TODO-FIXME: assert _owner == null implies _recursions = 0
247 return _contentions|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
248 }
249 const char* is_busy_to_string(stringStream* ss);
250
251 intptr_t is_entered(Thread* current) const;
252
253 void* owner() const;
254 void set_owner(void* owner);
255
256 jint waiters() const;
257
258 jint contentions() const;
259 intptr_t recursions() const { return _recursions; }
260
261 // JVM/TI GetObjectMonitorUsage() needs this:
262 ObjectWaiter* first_waiter() { return _WaitSet; }
263 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
264 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
265
266 protected:
267 // We don't typically expect or want the ctors or dtors to run.
268 // normal ObjectMonitors are type-stable and immortal.
269 ObjectMonitor() { ::memset((void*)this, 0, sizeof(*this)); }
270
271 ~ObjectMonitor() {
272 // TODO: Add asserts ...
273 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
274 // _contentions == 0 _EntryList == NULL etc
275 }
276
277 private:
278 void Recycle() {
279 // TODO: add stronger asserts ...
280 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
281 // _contentions == 0 EntryList == NULL
282 // _recursions == 0 _WaitSet == NULL
283 DEBUG_ONLY(stringStream ss;)
284 assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, "
285 "recursions=" INTPTR_FORMAT, is_busy_to_string(&ss), _recursions);
286 _succ = NULL;
287 _EntryList = NULL;
288 _cxq = NULL;
289 _WaitSet = NULL;
290 _recursions = 0;
291 }
292
293 public:
294
295 void* object() const;
296 void* object_addr();
297 void set_object(void* obj);
298
299 // Returns true if the specified thread owns the ObjectMonitor. Otherwise
300 // returns false and throws IllegalMonitorStateException (IMSE).
301 bool check_owner(Thread* THREAD);
302 void clear();
303
304 void enter(TRAPS);
305 void exit(bool not_suspended, TRAPS);
306 void wait(jlong millis, bool interruptable, TRAPS);
307 void notify(TRAPS);
308 void notifyAll(TRAPS);
309
310 void print() const;
311 void print_on(outputStream* st) const;
312
313 // Use the following at your own risk
314 intptr_t complete_exit(TRAPS);
315 void reenter(intptr_t recursions, TRAPS);
316
317 private:
318 void AddWaiter(ObjectWaiter* waiter);
319 void INotify(Thread* self);
320 ObjectWaiter* DequeueWaiter();
321 void DequeueSpecificWaiter(ObjectWaiter* waiter);
322 void EnterI(TRAPS);
323 void ReenterI(Thread* self, ObjectWaiter* self_node);
324 void UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node);
325 int TryLock(Thread* self);
326 int NotRunnable(Thread* self, Thread * Owner);
327 int TrySpin(Thread* self);
328 void ExitEpilog(Thread* self, ObjectWaiter* Wakee);
329 bool ExitSuspendEquivalent(JavaThread* self);
330 };
331
332 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP