1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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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 "oops/weakHandle.hpp"
32 #include "runtime/perfDataTypes.hpp"
33
34 class ObjectMonitor;
35 class ParkEvent;
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 JavaThread* _thread;
49 uint64_t _notifier_tid;
50 ParkEvent * _event;
51 volatile int _notified;
52 volatile TStates TState;
53 bool _active; // Contention monitoring is enabled
54 public:
55 ObjectWaiter(JavaThread* current);
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 #ifndef OM_CACHE_LINE_SIZE
124 // Use DEFAULT_CACHE_LINE_SIZE if not already specified for
125 // the current build platform.
126 #define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE
127 #endif
128
129 class ObjectMonitor : public CHeapObj<mtObjectMonitor> {
130 friend class ObjectSynchronizer;
131 friend class ObjectWaiter;
132 friend class VMStructs;
133 JVMCI_ONLY(friend class JVMCIVMStructs;)
134
135 static OopStorage* _oop_storage;
136
137 // The sync code expects the header field to be at offset zero (0).
138 // Enforced by the assert() in header_addr().
139 volatile markWord _header; // displaced object header word - mark
140 WeakHandle _object; // backward object pointer
141 // Separate _header and _owner on different cache lines since both can
142 // have busy multi-threaded access. _header and _object are set at initial
143 // inflation. The _object does not change, so it is a good choice to share
144 // its cache line with _header.
145 DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
146 sizeof(WeakHandle));
147 // Used by async deflation as a marker in the _owner field.
148 // Note that the choice of the two markers is peculiar:
149 // - They need to represent values that cannot be pointers. In particular,
150 // we achieve this by using the lowest two bits.
151 // - ANONYMOUS_OWNER should be a small value, it is used in generated code
152 // and small values encode much better.
153 // - We test for anonymous owner by testing for the lowest bit, therefore
154 // DEFLATER_MARKER must *not* have that bit set.
155 #define DEFLATER_MARKER reinterpret_cast<void*>(2)
156 public:
157 // NOTE: Typed as uintptr_t so that we can pick it up in SA, via vmStructs.
158 static const uintptr_t ANONYMOUS_OWNER = 1;
159
160 private:
161 static void* anon_owner_ptr() { return reinterpret_cast<void*>(ANONYMOUS_OWNER); }
162
163 void* volatile _owner; // pointer to owning thread OR BasicLock
164 volatile uint64_t _previous_owner_tid; // thread id of the previous owner of the monitor
165 // Separate _owner and _next_om on different cache lines since
166 // both can have busy multi-threaded access. _previous_owner_tid is only
167 // changed by ObjectMonitor::exit() so it is a good choice to share the
168 // cache line with _owner.
169 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
170 sizeof(volatile uint64_t));
171 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage
172 volatile intx _recursions; // recursion count, 0 for first entry
173 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry.
174 // The list is actually composed of WaitNodes,
175 // acting as proxies for Threads.
176
177 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry.
178 JavaThread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
179 JavaThread* volatile _Responsible;
180
181 volatile int _Spinner; // for exit->spinner handoff optimization
182 volatile int _SpinDuration;
183
184 int _contentions; // Number of active contentions in enter(). It is used by is_busy()
185 // along with other fields to determine if an ObjectMonitor can be
186 // deflated. It is also used by the async deflation protocol. See
187 // ObjectMonitor::deflate_monitor().
188 protected:
189 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor
190 volatile int _waiters; // number of waiting threads
191 private:
192 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
193
194 public:
195
196 static void Initialize();
197
198 // Only perform a PerfData operation if the PerfData object has been
199 // allocated and if the PerfDataManager has not freed the PerfData
200 // objects which can happen at normal VM shutdown.
201 //
202 #define OM_PERFDATA_OP(f, op_str) \
203 do { \
204 if (ObjectMonitor::_sync_ ## f != nullptr && \
205 PerfDataManager::has_PerfData()) { \
206 ObjectMonitor::_sync_ ## f->op_str; \
207 } \
208 } while (0)
209
210 static PerfCounter * _sync_ContendedLockAttempts;
211 static PerfCounter * _sync_FutileWakeups;
212 static PerfCounter * _sync_Parks;
213 static PerfCounter * _sync_Notifications;
214 static PerfCounter * _sync_Inflations;
215 static PerfCounter * _sync_Deflations;
216 static PerfLongVariable * _sync_MonExtant;
217
218 static int Knob_SpinLimit;
219
220 static ByteSize header_offset() { return byte_offset_of(ObjectMonitor, _header); }
221 static ByteSize owner_offset() { return byte_offset_of(ObjectMonitor, _owner); }
222 static ByteSize recursions_offset() { return byte_offset_of(ObjectMonitor, _recursions); }
223 static ByteSize cxq_offset() { return byte_offset_of(ObjectMonitor, _cxq); }
224 static ByteSize succ_offset() { return byte_offset_of(ObjectMonitor, _succ); }
225 static ByteSize EntryList_offset() { return byte_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 ((in_bytes(ObjectMonitor::f ## _offset())) - markWord::monitor_value)
240
241 markWord header() const;
242 volatile markWord* header_addr();
243 void set_header(markWord hdr);
244
245 bool is_busy() const {
246 // TODO-FIXME: assert _owner == null implies _recursions = 0
247 intptr_t ret_code = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList);
248 int cnts = contentions(); // read once
249 if (cnts > 0) {
250 ret_code |= intptr_t(cnts);
251 }
252 if (!owner_is_DEFLATER_MARKER()) {
253 ret_code |= intptr_t(owner_raw());
254 }
255 return ret_code != 0;
256 }
257 const char* is_busy_to_string(stringStream* ss);
258
259 bool is_entered(JavaThread* current) const;
260
261 // Returns true if this OM has an owner, false otherwise.
262 bool has_owner() const;
263 void* owner() const; // Returns null if DEFLATER_MARKER is observed.
264 void* owner_raw() const;
265 // Returns true if owner field == DEFLATER_MARKER and false otherwise.
266 bool owner_is_DEFLATER_MARKER() const;
267 // Returns true if 'this' is being async deflated and false otherwise.
268 bool is_being_async_deflated();
269 // Clear _owner field; current value must match old_value.
270 void release_clear_owner(void* old_value);
271 // Simply set _owner field to new_value; current value must match old_value.
272 void set_owner_from(void* old_value, void* new_value);
273 // Simply set _owner field to current; current value must match basic_lock_p.
274 void set_owner_from_BasicLock(void* basic_lock_p, JavaThread* current);
275 // Try to set _owner field to new_value if the current value matches
276 // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
277 // _owner field. Returns the prior value of the _owner field.
278 void* try_set_owner_from(void* old_value, void* new_value);
279
280 void set_owner_anonymous() {
281 set_owner_from(nullptr, anon_owner_ptr());
282 }
283
284 bool is_owner_anonymous() const {
285 return owner_raw() == anon_owner_ptr();
286 }
287
288 void set_owner_from_anonymous(Thread* owner) {
289 set_owner_from(anon_owner_ptr(), owner);
290 }
291
292 // Simply get _next_om field.
293 ObjectMonitor* next_om() const;
294 // Simply set _next_om field to new_value.
295 void set_next_om(ObjectMonitor* new_value);
296
297 int waiters() const;
298
299 int contentions() const;
300 void add_to_contentions(int value);
301 intx recursions() const { return _recursions; }
302 void set_recursions(size_t recursions);
303
304 // JVM/TI GetObjectMonitorUsage() needs this:
305 ObjectWaiter* first_waiter() { return _WaitSet; }
306 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
307 JavaThread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
308
309 ObjectMonitor(oop object);
310 ~ObjectMonitor();
311
312 oop object() const;
313 oop object_peek() const;
314
315 // Returns true if the specified thread owns the ObjectMonitor. Otherwise
316 // returns false and throws IllegalMonitorStateException (IMSE).
317 bool check_owner(TRAPS);
318
319 private:
320 class ExitOnSuspend {
321 protected:
322 ObjectMonitor* _om;
323 bool _om_exited;
324 public:
325 ExitOnSuspend(ObjectMonitor* om) : _om(om), _om_exited(false) {}
326 void operator()(JavaThread* current);
327 bool exited() { return _om_exited; }
328 };
329 class ClearSuccOnSuspend {
330 protected:
331 ObjectMonitor* _om;
332 public:
333 ClearSuccOnSuspend(ObjectMonitor* om) : _om(om) {}
334 void operator()(JavaThread* current);
335 };
336 public:
337 bool enter_for(JavaThread* locking_thread);
338 bool enter(JavaThread* current);
339 void exit(JavaThread* current, bool not_suspended = true);
340 void wait(jlong millis, bool interruptible, TRAPS);
341 void notify(TRAPS);
342 void notifyAll(TRAPS);
343
344 void print() const;
345 #ifdef ASSERT
346 void print_debug_style_on(outputStream* st) const;
347 #endif
348 void print_on(outputStream* st) const;
349
350 // Use the following at your own risk
351 intx complete_exit(JavaThread* current);
352
353 private:
354 void AddWaiter(ObjectWaiter* waiter);
355 void INotify(JavaThread* current);
356 ObjectWaiter* DequeueWaiter();
357 void DequeueSpecificWaiter(ObjectWaiter* waiter);
358 void EnterI(JavaThread* current);
359 void ReenterI(JavaThread* current, ObjectWaiter* current_node);
360 void UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* current_node);
361 int TryLock(JavaThread* current);
362 int NotRunnable(JavaThread* current, JavaThread* Owner);
363 int TrySpin(JavaThread* current);
364 void ExitEpilog(JavaThread* current, ObjectWaiter* Wakee);
365
366 // Deflation support
367 bool deflate_monitor();
368 void install_displaced_markword_in_object(const oop obj);
369 };
370
371 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP