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/os.hpp"
33 #include "runtime/park.hpp"
34 #include "runtime/perfDataTypes.hpp"
35
36 class ObjectMonitor;
37
38 // ObjectWaiter serves as a "proxy" or surrogate thread.
39 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
40 // ParkEvent instead. Beware, however, that the JVMTI code
41 // knows about ObjectWaiters, so we'll have to reconcile that code.
42 // See next_waiter(), first_waiter(), etc.
43
44 class ObjectWaiter : public StackObj {
45 public:
46 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
47 ObjectWaiter* volatile _next;
48 ObjectWaiter* volatile _prev;
49 JavaThread* _thread;
50 jlong _notifier_tid;
51 ParkEvent * _event;
52 volatile int _notified;
53 volatile TStates TState;
54 bool _active; // Contention monitoring is enabled
55 public:
56 ObjectWaiter(JavaThread* current);
57
58 void wait_reenter_begin(ObjectMonitor *mon);
59 void wait_reenter_end(ObjectMonitor *mon);
60 };
61
62 // The ObjectMonitor class implements the heavyweight version of a
63 // JavaMonitor. The lightweight BasicLock/stack lock version has been
64 // inflated into an ObjectMonitor. This inflation is typically due to
65 // contention or use of Object.wait().
66 //
67 // WARNING: This is a very sensitive and fragile class. DO NOT make any
68 // changes unless you are fully aware of the underlying semantics.
69 //
70 // ObjectMonitor Layout Overview/Highlights/Restrictions:
71 //
72 // - The _header field must be at offset 0 because the displaced header
73 // from markWord is stored there. We do not want markWord.hpp to include
74 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
75 // means that ObjectMonitor cannot inherit from any other class nor can
76 // it use any virtual member functions. This restriction is critical to
77 // the proper functioning of the VM.
78 // - The _header and _owner fields should be separated by enough space
79 // to avoid false sharing due to parallel access by different threads.
80 // This is an advisory recommendation.
81 // - The general layout of the fields in ObjectMonitor is:
82 // _header
83 // <lightly_used_fields>
84 // <optional padding>
85 // _owner
86 // <remaining_fields>
87 // - The VM assumes write ordering and machine word alignment with
88 // respect to the _owner field and the <remaining_fields> that can
89 // be read in parallel by other threads.
90 // - Generally fields that are accessed closely together in time should
91 // be placed proximally in space to promote data cache locality. That
92 // is, temporal locality should condition spatial locality.
93 // - We have to balance avoiding false sharing with excessive invalidation
94 // from coherence traffic. As such, we try to cluster fields that tend
95 // to be _written_ at approximately the same time onto the same data
96 // cache line.
97 // - We also have to balance the natural tension between minimizing
98 // single threaded capacity misses with excessive multi-threaded
99 // coherency misses. There is no single optimal layout for both
100 // single-threaded and multi-threaded environments.
101 //
102 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
103 // enforced.
104 // - Adjacent ObjectMonitors should be separated by enough space to avoid
105 // false sharing. This is handled by the ObjectMonitor allocation code
106 // in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
107 //
108 // Futures notes:
109 // - Separating _owner from the <remaining_fields> by enough space to
110 // avoid false sharing might be profitable. Given
111 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
112 // we know that the CAS in monitorenter will invalidate the line
113 // underlying _owner. We want to avoid an L1 data cache miss on that
114 // same line for monitorexit. Putting these <remaining_fields>:
115 // _recursions, _EntryList, _cxq, and _succ, all of which may be
116 // fetched in the inflated unlock path, on a different cache line
117 // would make them immune to CAS-based invalidation from the _owner
118 // field.
119 //
120 // - The _recursions field should be of type int, or int32_t but not
121 // intptr_t. There's no reason to use a 64-bit type for this field
122 // in a 64-bit JVM.
123
124 #ifndef OM_CACHE_LINE_SIZE
125 // Use DEFAULT_CACHE_LINE_SIZE if not already specified for
126 // the current build platform.
127 #define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE
128 #endif
129
130 class ObjectMonitor : public CHeapObj<mtObjectMonitor> {
131 friend class ObjectSynchronizer;
132 friend class ObjectWaiter;
133 friend class VMStructs;
134 JVMCI_ONLY(friend class JVMCIVMStructs;)
135
136 static OopStorage* _oop_storage;
137
138 // The sync code expects the header field to be at offset zero (0).
139 // Enforced by the assert() in header_addr().
140 volatile markWord _header; // displaced object header word - mark
141 WeakHandle _object; // backward object pointer
142 // Separate _header and _owner on different cache lines since both can
143 // have busy multi-threaded access. _header and _object are set at initial
144 // inflation. The _object does not change, so it is a good choice to share
145 // its cache line with _header.
146 DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
147 sizeof(WeakHandle));
148 // Used by async deflation as a marker in the _owner field:
149 #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
150 void* volatile _owner; // pointer to owning thread OR BasicLock
151 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
152 // Separate _owner and _next_om on different cache lines since
153 // both can have busy multi-threaded access. _previous_owner_tid is only
154 // changed by ObjectMonitor::exit() so it is a good choice to share the
155 // cache line with _owner.
156 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
157 sizeof(volatile jlong));
158 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage
159 volatile intx _recursions; // recursion count, 0 for first entry
160 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry.
161 // The list is actually composed of WaitNodes,
162 // acting as proxies for Threads.
163
164 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry.
165 JavaThread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
166 JavaThread* volatile _Responsible;
167
168 volatile int _Spinner; // for exit->spinner handoff optimization
169 volatile int _SpinDuration;
170
171 jint _contentions; // Number of active contentions in enter(). It is used by is_busy()
172 // along with other fields to determine if an ObjectMonitor can be
173 // deflated. It is also used by the async deflation protocol. See
174 // ObjectMonitor::deflate_monitor().
175 protected:
176 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor
177 volatile jint _waiters; // number of waiting threads
178 private:
179 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
180
181 public:
182 static void Initialize();
183
184 // Only perform a PerfData operation if the PerfData object has been
185 // allocated and if the PerfDataManager has not freed the PerfData
186 // objects which can happen at normal VM shutdown.
187 //
188 #define OM_PERFDATA_OP(f, op_str) \
189 do { \
190 if (ObjectMonitor::_sync_ ## f != NULL && \
191 PerfDataManager::has_PerfData()) { \
192 ObjectMonitor::_sync_ ## f->op_str; \
193 } \
194 } while (0)
195
196 static PerfCounter * _sync_ContendedLockAttempts;
197 static PerfCounter * _sync_FutileWakeups;
198 static PerfCounter * _sync_Parks;
199 static PerfCounter * _sync_Notifications;
200 static PerfCounter * _sync_Inflations;
201 static PerfCounter * _sync_Deflations;
202 static PerfLongVariable * _sync_MonExtant;
203
204 static int Knob_SpinLimit;
205
206 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
207 // ByteSize would also be an appropriate type.
208 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); }
209 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); }
210 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); }
211 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
212 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); }
213 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); }
214 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
215
216 // ObjectMonitor references can be ORed with markWord::monitor_value
217 // as part of the ObjectMonitor tagging mechanism. When we combine an
218 // ObjectMonitor reference with an offset, we need to remove the tag
219 // value in order to generate the proper address.
220 //
221 // We can either adjust the ObjectMonitor reference and then add the
222 // offset or we can adjust the offset that is added to the ObjectMonitor
223 // reference. The latter avoids an AGI (Address Generation Interlock)
224 // stall so the helper macro adjusts the offset value that is returned
225 // to the ObjectMonitor reference manipulation code:
226 //
227 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
228 ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value)
229
230 markWord header() const;
231 volatile markWord* header_addr();
232 void set_header(markWord hdr);
233
234 bool is_busy() const {
235 // TODO-FIXME: assert _owner == null implies _recursions = 0
236 intptr_t ret_code = _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
237 if (contentions() > 0) {
238 ret_code |= contentions();
239 }
240 if (!owner_is_DEFLATER_MARKER()) {
241 ret_code |= intptr_t(owner_raw());
242 }
243 return ret_code != 0;
244 }
245 const char* is_busy_to_string(stringStream* ss);
246
247 intptr_t is_entered(JavaThread* current) const;
248
249 void* owner() const; // Returns NULL if DEFLATER_MARKER is observed.
250 void* owner_raw() const;
251 // Returns true if owner field == DEFLATER_MARKER and false otherwise.
252 bool owner_is_DEFLATER_MARKER() const;
253 // Returns true if 'this' is being async deflated and false otherwise.
254 bool is_being_async_deflated();
255 // Clear _owner field; current value must match old_value.
256 void release_clear_owner(void* old_value);
257 // Simply set _owner field to new_value; current value must match old_value.
258 void set_owner_from(void* old_value, void* new_value);
259 // Simply set _owner field to current; current value must match basic_lock_p.
260 void set_owner_from_BasicLock(void* basic_lock_p, JavaThread* current);
261 // Try to set _owner field to new_value if the current value matches
262 // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
263 // _owner field. Returns the prior value of the _owner field.
264 void* try_set_owner_from(void* old_value, void* new_value);
265
266 // Simply get _next_om field.
267 ObjectMonitor* next_om() const;
268 // Get _next_om field with acquire semantics.
269 ObjectMonitor* next_om_acquire() const;
270 // Simply set _next_om field to new_value.
271 void set_next_om(ObjectMonitor* new_value);
272 // Set _next_om field to new_value with release semantics.
273 void release_set_next_om(ObjectMonitor* new_value);
274 // Try to set _next_om field to new_value if the current value matches
275 // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
276 // _next_om field. Returns the prior value of the _next_om field.
277 ObjectMonitor* try_set_next_om(ObjectMonitor* old_value, ObjectMonitor* new_value);
278
279 jint waiters() const;
280
281 jint contentions() const;
282 void add_to_contentions(jint value);
283 intx recursions() const { return _recursions; }
284
285 // JVM/TI GetObjectMonitorUsage() needs this:
286 ObjectWaiter* first_waiter() { return _WaitSet; }
287 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
288 JavaThread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
289
290 ObjectMonitor(oop object);
291 ~ObjectMonitor();
292
293 oop object() const;
294 oop object_peek() const;
295
296 // Returns true if the specified thread owns the ObjectMonitor. Otherwise
297 // returns false and throws IllegalMonitorStateException (IMSE).
298 bool check_owner(TRAPS);
299
300 private:
301 class ExitOnSuspend {
302 protected:
303 ObjectMonitor* _om;
304 bool _om_exited;
305 public:
306 ExitOnSuspend(ObjectMonitor* om) : _om(om), _om_exited(false) {}
307 void operator()(JavaThread* current);
308 bool exited() { return _om_exited; }
309 };
310 class ClearSuccOnSuspend {
311 protected:
312 ObjectMonitor* _om;
313 public:
314 ClearSuccOnSuspend(ObjectMonitor* om) : _om(om) {}
315 void operator()(JavaThread* current);
316 };
317 public:
318 bool enter(JavaThread* current);
319 void exit(JavaThread* current, bool not_suspended = true);
320 void wait(jlong millis, bool interruptible, TRAPS);
321 void notify(TRAPS);
322 void notifyAll(TRAPS);
323
324 void print() const;
325 #ifdef ASSERT
326 void print_debug_style_on(outputStream* st) const;
327 #endif
328 void print_on(outputStream* st) const;
329
330 // Use the following at your own risk
331 intx complete_exit(JavaThread* current);
332 bool reenter(intx recursions, JavaThread* current);
333
334 private:
335 void AddWaiter(ObjectWaiter* waiter);
336 void INotify(JavaThread* current);
337 ObjectWaiter* DequeueWaiter();
338 void DequeueSpecificWaiter(ObjectWaiter* waiter);
339 void EnterI(JavaThread* current);
340 void ReenterI(JavaThread* current, ObjectWaiter* current_node);
341 void UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* current_node);
342 int TryLock(JavaThread* current);
343 int NotRunnable(JavaThread* current, JavaThread* Owner);
344 int TrySpin(JavaThread* current);
345 void ExitEpilog(JavaThread* current, ObjectWaiter* Wakee);
346
347 // Deflation support
348 bool deflate_monitor();
349 void install_displaced_markword_in_object(const oop obj);
350 };
351
352 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP