1 /*
2 * Copyright (c) 1998, 2018, Oracle and/or its affiliates. All rights reserved.
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
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
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24
25 #ifndef SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
26 #define SHARE_VM_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 ObjectSynchronizer;
140 friend class ObjectWaiter;
141 friend class VMStructs;
142
143 volatile markOop _header; // displaced object header word - mark
144 void* volatile _object; // backward object pointer - strong root
145 public:
146 ObjectMonitor* FreeNext; // Free list linkage
147 private:
148 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
149 sizeof(volatile markOop) + sizeof(void * volatile) +
150 sizeof(ObjectMonitor *));
151 protected: // protected for JvmtiRawMonitor
152 void * volatile _owner; // pointer to owning thread OR BasicLock
153 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
154 volatile intptr_t _recursions; // recursion count, 0 for first entry
155 ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry.
156 // The list is actually composed of WaitNodes,
157 // acting as proxies for Threads.
158 private:
159 ObjectWaiter * volatile _cxq; // LL of recently-arrived threads blocked on entry.
160 Thread * volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
161 Thread * volatile _Responsible;
162
163 volatile int _Spinner; // for exit->spinner handoff optimization
164 volatile int _SpinDuration;
165
166 volatile jint _count; // reference count to prevent reclamation/deflation
167 // at stop-the-world time. See deflate_idle_monitors().
168 // _count is approximately |_WaitSet| + |_EntryList|
169 protected:
170 ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
171 volatile jint _waiters; // number of waiting threads
172 private:
173 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
174
175 public:
176 static void Initialize();
177
178 // Only perform a PerfData operation if the PerfData object has been
179 // allocated and if the PerfDataManager has not freed the PerfData
180 // objects which can happen at normal VM shutdown.
181 //
182 #define OM_PERFDATA_OP(f, op_str) \
183 do { \
184 if (ObjectMonitor::_sync_ ## f != NULL && \
185 PerfDataManager::has_PerfData()) { \
186 ObjectMonitor::_sync_ ## f->op_str; \
187 } \
188 } while (0)
189
190 static PerfCounter * _sync_ContendedLockAttempts;
191 static PerfCounter * _sync_FutileWakeups;
192 static PerfCounter * _sync_Parks;
193 static PerfCounter * _sync_Notifications;
194 static PerfCounter * _sync_Inflations;
195 static PerfCounter * _sync_Deflations;
196 static PerfLongVariable * _sync_MonExtant;
197
198 static int Knob_VerifyMatch;
199 static int Knob_SpinLimit;
200
201 void* operator new (size_t size) throw();
202 void* operator new[] (size_t size) throw();
203 void operator delete(void* p);
204 void operator delete[] (void *p);
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 count_offset_in_bytes() { return offset_of(ObjectMonitor, _count); }
212 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
213 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); }
214 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); }
215 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
216
217 // ObjectMonitor references can be ORed with markOopDesc::monitor_value
218 // as part of the ObjectMonitor tagging mechanism. When we combine an
219 // ObjectMonitor reference with an offset, we need to remove the tag
220 // value in order to generate the proper address.
221 //
222 // We can either adjust the ObjectMonitor reference and then add the
223 // offset or we can adjust the offset that is added to the ObjectMonitor
224 // reference. The latter avoids an AGI (Address Generation Interlock)
225 // stall so the helper macro adjusts the offset value that is returned
226 // to the ObjectMonitor reference manipulation code:
227 //
228 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
229 ((ObjectMonitor::f ## _offset_in_bytes()) - markOopDesc::monitor_value)
230
231 markOop header() const;
232 volatile markOop* header_addr();
233 void set_header(markOop hdr);
234
235 intptr_t is_busy() const {
236 // TODO-FIXME: merge _count and _waiters.
237 // TODO-FIXME: assert _owner == null implies _recursions = 0
238 // TODO-FIXME: assert _WaitSet != null implies _count > 0
239 return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
240 }
241
242 intptr_t is_entered(Thread* current) const;
243
244 void* owner() const;
245 void set_owner(void* owner);
246
247 jint waiters() const;
248
249 jint count() const;
250 void set_count(jint count);
251 jint contentions() const;
252 intptr_t recursions() const { return _recursions; }
253
254 // JVM/TI GetObjectMonitorUsage() needs this:
255 ObjectWaiter* first_waiter() { return _WaitSet; }
256 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
257 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
258
259 protected:
260 // We don't typically expect or want the ctors or dtors to run.
261 // normal ObjectMonitors are type-stable and immortal.
262 ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); }
263
264 ~ObjectMonitor() {
265 // TODO: Add asserts ...
266 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
267 // _count == 0 _EntryList == NULL etc
268 }
269
270 private:
271 void Recycle() {
272 // TODO: add stronger asserts ...
273 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
274 // _count == 0 EntryList == NULL
275 // _recursions == 0 _WaitSet == NULL
276 assert(((is_busy()|_recursions) == 0), "freeing inuse monitor");
277 _succ = NULL;
278 _EntryList = NULL;
279 _cxq = NULL;
280 _WaitSet = NULL;
281 _recursions = 0;
282 }
283
284 public:
285
286 void* object() const;
287 void* object_addr();
288 void set_object(void* obj);
289
290 bool check(TRAPS); // true if the thread owns the monitor.
291 void check_slow(TRAPS);
292 void clear();
293
294 void enter(TRAPS);
295 void exit(bool not_suspended, TRAPS);
296 void wait(jlong millis, bool interruptable, TRAPS);
297 void notify(TRAPS);
298 void notifyAll(TRAPS);
299
300 // Use the following at your own risk
301 intptr_t complete_exit(TRAPS);
302 void reenter(intptr_t recursions, TRAPS);
303
304 private:
305 void AddWaiter(ObjectWaiter * waiter);
306 static void DeferredInitialize();
307 void INotify(Thread * Self);
308 ObjectWaiter * DequeueWaiter();
309 void DequeueSpecificWaiter(ObjectWaiter * waiter);
310 void EnterI(TRAPS);
311 void ReenterI(Thread * Self, ObjectWaiter * SelfNode);
312 void UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode);
313 int TryLock(Thread * Self);
314 int NotRunnable(Thread * Self, Thread * Owner);
315 int TrySpin(Thread * Self);
316 void ExitEpilog(Thread * Self, ObjectWaiter * Wakee);
317 bool ExitSuspendEquivalent(JavaThread * Self);
318 };
319
320 #endif // SHARE_VM_RUNTIME_OBJECTMONITOR_HPP