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