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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7 * published by the Free Software Foundation.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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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 "runtime/os.hpp"
31 #include "runtime/park.hpp"
32 #include "runtime/perfData.hpp"
33
34 class ObjectMonitor;
35
36 // ObjectWaiter serves as a "proxy" or surrogate thread.
37 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
38 // ParkEvent instead. Beware, however, that the JVMTI code
39 // knows about ObjectWaiters, so we'll have to reconcile that code.
40 // See next_waiter(), first_waiter(), etc.
41
42 class ObjectWaiter : public StackObj {
43 public:
44 enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
45 enum Sorted { PREPEND, APPEND, SORTED };
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 Sorted _Sorted; // List placement disposition
54 bool _active; // Contention monitoring is enabled
55 public:
56 ObjectWaiter(Thread* thread);
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 // Class JvmtiRawMonitor currently inherits from ObjectMonitor so
71 // changes in this class must be careful to not break JvmtiRawMonitor.
72 // These two subsystems should be separated.
73 //
74 // ObjectMonitor Layout Overview/Highlights/Restrictions:
75 //
76 // - The _header field must be at offset 0 because the displaced header
77 // from markOop is stored there. We do not want markOop.hpp to include
78 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
79 // means that ObjectMonitor cannot inherit from any other class nor can
80 // it use any virtual member functions. This restriction is critical to
81 // the proper functioning of the VM.
82 // - The _header and _owner fields should be separated by enough space
83 // to avoid false sharing due to parallel access by different threads.
84 // This is an advisory recommendation.
85 // - The general layout of the fields in ObjectMonitor is:
86 // _header
87 // <lightly_used_fields>
88 // <optional padding>
89 // _owner
90 // <remaining_fields>
91 // - The VM assumes write ordering and machine word alignment with
92 // respect to the _owner field and the <remaining_fields> that can
93 // be read in parallel by other threads.
94 // - Generally fields that are accessed closely together in time should
95 // be placed proximally in space to promote data cache locality. That
96 // is, temporal locality should condition spatial locality.
97 // - We have to balance avoiding false sharing with excessive invalidation
98 // from coherence traffic. As such, we try to cluster fields that tend
99 // to be _written_ at approximately the same time onto the same data
100 // cache line.
101 // - We also have to balance the natural tension between minimizing
102 // single threaded capacity misses with excessive multi-threaded
103 // coherency misses. There is no single optimal layout for both
104 // single-threaded and multi-threaded environments.
105 //
106 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
107 // enforced.
108 // - Adjacent ObjectMonitors should be separated by enough space to avoid
109 // false sharing. This is handled by the ObjectMonitor allocation code
110 // in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
111 //
112 // Futures notes:
113 // - Separating _owner from the <remaining_fields> by enough space to
114 // avoid false sharing might be profitable. Given
115 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
116 // we know that the CAS in monitorenter will invalidate the line
117 // underlying _owner. We want to avoid an L1 data cache miss on that
118 // same line for monitorexit. Putting these <remaining_fields>:
119 // _recursions, _EntryList, _cxq, and _succ, all of which may be
120 // fetched in the inflated unlock path, on a different cache line
121 // would make them immune to CAS-based invalidation from the _owner
122 // field.
123 //
124 // - The _recursions field should be of type int, or int32_t but not
125 // intptr_t. There's no reason to use a 64-bit type for this field
126 // in a 64-bit JVM.
127
128 class ObjectMonitor {
129 public:
130 enum {
131 OM_OK, // no error
132 OM_SYSTEM_ERROR, // operating system error
133 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
134 OM_INTERRUPTED, // Thread.interrupt()
135 OM_TIMED_OUT // Object.wait() timed out
136 };
137
138 private:
139 friend class ObjectMonitorHandle;
140 friend class ObjectSynchronizer;
141 friend class ObjectWaiter;
142 friend class VMStructs;
143
144 volatile markOop _header; // displaced object header word - mark
145 void* volatile _object; // backward object pointer - strong root
146 public:
147 ObjectMonitor* FreeNext; // Free list linkage
148 private:
149 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
150 sizeof(volatile markOop) + sizeof(void * volatile) +
151 sizeof(ObjectMonitor *));
152 protected: // protected for JvmtiRawMonitor
153 // Used by async deflation as a marker in the _owner field:
154 #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
155 void * volatile _owner; // pointer to owning thread OR BasicLock
156 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
157 volatile intptr_t _recursions; // recursion count, 0 for first entry
158 ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry.
159 // The list is actually composed of WaitNodes,
160 // acting as proxies for Threads.
161 private:
162 ObjectWaiter * volatile _cxq; // LL of recently-arrived threads blocked on entry.
163 Thread * volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
164 Thread * volatile _Responsible;
165
166 volatile int _Spinner; // for exit->spinner handoff optimization
167 volatile int _SpinDuration;
168
169 volatile jint _contentions; // Number of active contentions in enter(). It is used by is_busy()
170 // along with other fields to determine if an ObjectMonitor can be
171 // deflated. See ObjectSynchronizer::deflate_monitor() and
172 // ObjectSynchronizer::deflate_monitor_using_JT().
173 protected:
174 ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
175 volatile jint _waiters; // number of waiting threads
176 private:
177 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
178 volatile jint _ref_count; // ref count for ObjectMonitor* and used by the async deflation
179 // protocol. See ObjectSynchronizer::deflate_monitor_using_JT().
180 typedef enum {
181 Free = 0, // Free must be 0 for monitor to be free after memset(..,0,..).
182 New,
183 Old
184 } AllocationState;
185 AllocationState _allocation_state;
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 markOopDesc::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()) - markOopDesc::monitor_value)
240
241 markOop header() const;
242 volatile markOop* header_addr();
243 void set_header(markOop hdr);
244
245 intptr_t is_busy() const {
246 // TODO-FIXME: assert _owner == null implies _recursions = 0
247 // We do not include _ref_count in the is_busy() check because
248 // _ref_count is for indicating that the ObjectMonitor* is in
249 // use which is orthogonal to whether the ObjectMonitor itself
250 // is in use for a locking operation.
251 return _contentions|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
252 }
253
254 // Version of is_busy() that accounts for the special value in
255 // _owner when AsyncDeflateIdleMonitors is enabled.
256 intptr_t is_busy_async() const {
257 intptr_t ret_code = _contentions | _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
258 if (!AsyncDeflateIdleMonitors) {
259 ret_code |= intptr_t(_owner);
260 } else {
261 if (_owner != DEFLATER_MARKER) {
262 ret_code |= intptr_t(_owner);
263 }
264 }
265 return ret_code;
266 }
267
268 intptr_t is_entered(Thread* current) const;
269
270 void* owner() const; // Returns NULL if DEFLATER_MARKER is observed.
271 void set_owner(void* owner);
272
273 jint waiters() const;
274
275 jint contentions() const;
276 intptr_t recursions() const { return _recursions; }
277
278 // JVM/TI GetObjectMonitorUsage() needs this:
279 ObjectWaiter* first_waiter() { return _WaitSet; }
280 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
281 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
282
283 protected:
284 // We don't typically expect or want the ctors or dtors to run.
285 // normal ObjectMonitors are type-stable and immortal.
286 ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); }
287
288 ~ObjectMonitor() {
289 // TODO: Add asserts ...
290 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
291 // _contentions == 0 _EntryList == NULL etc
292 }
293
294 private:
295 void Recycle() {
296 // TODO: add stronger asserts ...
297 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
298 // _contentions == 0 EntryList == NULL
299 // _recursions == 0 _WaitSet == NULL
300 assert(((is_busy()|_recursions) == 0), "freeing inuse monitor");
301 _succ = NULL;
302 _EntryList = NULL;
303 _cxq = NULL;
304 _WaitSet = NULL;
305 _recursions = 0;
306 }
307
308 public:
309
310 void* object() const;
311 void* object_addr();
312 void set_object(void* obj);
313 void set_allocation_state(AllocationState s);
314 AllocationState allocation_state() const;
315 bool is_free() const;
316 bool is_active() const;
317 bool is_old() const;
318 bool is_new() const;
319 void dec_ref_count();
320 void inc_ref_count();
321 jint ref_count() const;
322
323 bool check(TRAPS); // true if the thread owns the monitor.
324 void check_slow(TRAPS);
325 void clear();
326 void clear_using_JT();
327
328 void enter(TRAPS);
329 void exit(bool not_suspended, TRAPS);
330 void wait(jlong millis, bool interruptable, TRAPS);
331 void notify(TRAPS);
332 void notifyAll(TRAPS);
333
334 // Use the following at your own risk
335 intptr_t complete_exit(TRAPS);
336 void reenter(intptr_t recursions, TRAPS);
337
338 private:
339 void AddWaiter(ObjectWaiter * waiter);
340 void INotify(Thread * Self);
341 ObjectWaiter * DequeueWaiter();
342 void DequeueSpecificWaiter(ObjectWaiter * waiter);
343 void EnterI(TRAPS);
344 void ReenterI(Thread * Self, ObjectWaiter * SelfNode);
345 void UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode);
346 int TryLock(Thread * Self);
347 int NotRunnable(Thread * Self, Thread * Owner);
348 int TrySpin(Thread * Self);
349 void ExitEpilog(Thread * Self, ObjectWaiter * Wakee);
350 bool ExitSuspendEquivalent(JavaThread * Self);
351 void install_displaced_markword_in_object(const oop obj);
352 };
353
354 // A helper object for managing an ObjectMonitor*'s ref_count. There
355 // are special safety considerations when async deflation is used.
356 class ObjectMonitorHandle : public StackObj {
357 private:
358 ObjectMonitor * _om_ptr;
359 public:
360 ObjectMonitorHandle() { _om_ptr = NULL; }
361 ~ObjectMonitorHandle();
362
363 ObjectMonitor * om_ptr() const { return _om_ptr; }
364 // Save the ObjectMonitor* associated with the specified markOop and
365 // increment the ref_count.
366 bool save_om_ptr(oop object, markOop mark);
367
368 // For internal used by ObjectSynchronizer::monitors_iterate().
369 ObjectMonitorHandle(ObjectMonitor * _om_ptr);
370 // For internal use by ObjectSynchronizer::inflate().
371 void set_om_ptr(ObjectMonitor * om_ptr);
372 };
373
374 // Macro to use guarantee() for more strict AsyncDeflateIdleMonitors
375 // checks and assert() otherwise.
376 #define ADIM_guarantee(p, ...) \
377 do { \
378 if (AsyncDeflateIdleMonitors) { \
379 guarantee(p, __VA_ARGS__); \
380 } else { \
381 assert(p, __VA_ARGS__); \
382 } \
383 } while (0)
384
385 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP