1 /*
2 * Copyright (c) 1998, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
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 enum Sorted { PREPEND, APPEND, SORTED };
47 ObjectWaiter* volatile _next;
48 ObjectWaiter* volatile _prev;
49 Thread* _thread;
50 jlong _notifier_tid;
51 ParkEvent * _event;
52 volatile int _notified;
53 volatile TStates TState;
54 Sorted _Sorted; // List placement disposition
55 bool _active; // Contention monitoring is enabled
56 public:
57 ObjectWaiter(Thread* thread);
58
59 void wait_reenter_begin(ObjectMonitor *mon);
60 void wait_reenter_end(ObjectMonitor *mon);
61 };
62
63 // The ObjectMonitor class implements the heavyweight version of a
64 // JavaMonitor. The lightweight BasicLock/stack lock version has been
65 // inflated into an ObjectMonitor. This inflation is typically due to
66 // contention or use of Object.wait().
67 //
68 // WARNING: This is a very sensitive and fragile class. DO NOT make any
69 // changes unless you are fully aware of the underlying semantics.
70 //
71 // Class JvmtiRawMonitor currently inherits from ObjectMonitor so
72 // changes in this class must be careful to not break JvmtiRawMonitor.
73 // These two subsystems should be separated.
74 //
75 // ObjectMonitor Layout Overview/Highlights/Restrictions:
76 //
77 // - The _header field must be at offset 0 because the displaced header
78 // from markWord is stored there. We do not want markWord.hpp to include
79 // ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
80 // means that ObjectMonitor cannot inherit from any other class nor can
81 // it use any virtual member functions. This restriction is critical to
82 // the proper functioning of the VM.
83 // - The _header and _owner fields should be separated by enough space
84 // to avoid false sharing due to parallel access by different threads.
85 // This is an advisory recommendation.
86 // - The general layout of the fields in ObjectMonitor is:
87 // _header
88 // <lightly_used_fields>
89 // <optional padding>
90 // _owner
91 // <remaining_fields>
92 // - The VM assumes write ordering and machine word alignment with
93 // respect to the _owner field and the <remaining_fields> that can
94 // be read in parallel by other threads.
95 // - Generally fields that are accessed closely together in time should
96 // be placed proximally in space to promote data cache locality. That
97 // is, temporal locality should condition spatial locality.
98 // - We have to balance avoiding false sharing with excessive invalidation
99 // from coherence traffic. As such, we try to cluster fields that tend
100 // to be _written_ at approximately the same time onto the same data
101 // cache line.
102 // - We also have to balance the natural tension between minimizing
103 // single threaded capacity misses with excessive multi-threaded
104 // coherency misses. There is no single optimal layout for both
105 // single-threaded and multi-threaded environments.
106 //
107 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
108 // enforced.
109 // - Adjacent ObjectMonitors should be separated by enough space to avoid
110 // false sharing. This is handled by the ObjectMonitor allocation code
111 // in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
112 //
113 // Futures notes:
114 // - Separating _owner from the <remaining_fields> by enough space to
115 // avoid false sharing might be profitable. Given
116 // http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
117 // we know that the CAS in monitorenter will invalidate the line
118 // underlying _owner. We want to avoid an L1 data cache miss on that
119 // same line for monitorexit. Putting these <remaining_fields>:
120 // _recursions, _EntryList, _cxq, and _succ, all of which may be
121 // fetched in the inflated unlock path, on a different cache line
122 // would make them immune to CAS-based invalidation from the _owner
123 // field.
124 //
125 // - The _recursions field should be of type int, or int32_t but not
126 // intptr_t. There's no reason to use a 64-bit type for this field
127 // in a 64-bit JVM.
128
129 class ObjectMonitor {
130 public:
131 enum {
132 OM_OK, // no error
133 OM_SYSTEM_ERROR, // operating system error
134 OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
135 OM_INTERRUPTED, // Thread.interrupt()
136 OM_TIMED_OUT // Object.wait() timed out
137 };
138
139 private:
140 friend class ObjectMonitorHandle;
141 friend class ObjectSynchronizer;
142 friend class ObjectWaiter;
143 friend class VMStructs;
144 JVMCI_ONLY(friend class JVMCIVMStructs;)
145
146 // The sync code expects the header field to be at offset zero (0).
147 // Enforced by the assert() in header_addr().
148 volatile markWord _header; // displaced object header word - mark
149 void* volatile _object; // backward object pointer - strong root
150 public:
151 ObjectMonitor* _next_om; // Next ObjectMonitor* linkage
152 private:
153 // Separate _header and _owner on different cache lines since both can
154 // have busy multi-threaded access. _header and _object are set at
155 // initial inflation and _object doesn't change until deflation so
156 // _object is a good choice to share the cache line with _header.
157 // _next_om shares _header's cache line for pre-monitor list historical
158 // reasons. _next_om only changes if the next ObjectMonitor is deflated.
159 DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
160 sizeof(volatile markWord) + sizeof(void* volatile) +
161 sizeof(ObjectMonitor *));
162 // Used by async deflation as a marker in the _owner field:
163 #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
164 protected: // protected for JvmtiRawMonitor
165 void* volatile _owner; // pointer to owning thread OR BasicLock
166 private:
167 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
168 protected: // protected for JvmtiRawMonitor
169 volatile intptr_t _recursions; // recursion count, 0 for first entry
170 ObjectWaiter* volatile _EntryList; // Threads blocked on entry or reentry.
171 // The list is actually composed of WaitNodes,
172 // acting as proxies for Threads.
173 private:
174 ObjectWaiter* volatile _cxq; // LL of recently-arrived threads blocked on entry.
175 Thread* volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
176 Thread* volatile _Responsible;
177
178 volatile int _Spinner; // for exit->spinner handoff optimization
179 volatile int _SpinDuration;
180
181 volatile jint _contentions; // Number of active contentions in enter(). It is used by is_busy()
182 // along with other fields to determine if an ObjectMonitor can be
183 // deflated. See ObjectSynchronizer::deflate_monitor() and
184 // ObjectSynchronizer::deflate_monitor_using_JT().
185 protected:
186 ObjectWaiter* volatile _WaitSet; // LL of threads wait()ing on the monitor
187 volatile jint _waiters; // number of waiting threads
188 private:
189 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
190 volatile jint _ref_count; // ref count for ObjectMonitor* and used by the async deflation
191 // protocol. See ObjectSynchronizer::deflate_monitor_using_JT().
192 typedef enum {
193 Free = 0, // Free must be 0 for monitor to be free after memset(..,0,..).
194 New,
195 Old
196 } AllocationState;
197 AllocationState _allocation_state;
198
199 public:
200 static void Initialize();
201
202 // Only perform a PerfData operation if the PerfData object has been
203 // allocated and if the PerfDataManager has not freed the PerfData
204 // objects which can happen at normal VM shutdown.
205 //
206 #define OM_PERFDATA_OP(f, op_str) \
207 do { \
208 if (ObjectMonitor::_sync_ ## f != NULL && \
209 PerfDataManager::has_PerfData()) { \
210 ObjectMonitor::_sync_ ## f->op_str; \
211 } \
212 } while (0)
213
214 static PerfCounter * _sync_ContendedLockAttempts;
215 static PerfCounter * _sync_FutileWakeups;
216 static PerfCounter * _sync_Parks;
217 static PerfCounter * _sync_Notifications;
218 static PerfCounter * _sync_Inflations;
219 static PerfCounter * _sync_Deflations;
220 static PerfLongVariable * _sync_MonExtant;
221
222 static int Knob_SpinLimit;
223
224 void* operator new (size_t size) throw();
225 void* operator new[] (size_t size) throw();
226 void operator delete(void* p);
227 void operator delete[] (void* p);
228
229 // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
230 // ByteSize would also be an appropriate type.
231 static int header_offset_in_bytes() { return offset_of(ObjectMonitor, _header); }
232 static int object_offset_in_bytes() { return offset_of(ObjectMonitor, _object); }
233 static int owner_offset_in_bytes() { return offset_of(ObjectMonitor, _owner); }
234 static int recursions_offset_in_bytes() { return offset_of(ObjectMonitor, _recursions); }
235 static int cxq_offset_in_bytes() { return offset_of(ObjectMonitor, _cxq); }
236 static int succ_offset_in_bytes() { return offset_of(ObjectMonitor, _succ); }
237 static int EntryList_offset_in_bytes() { return offset_of(ObjectMonitor, _EntryList); }
238
239 // ObjectMonitor references can be ORed with markWord::monitor_value
240 // as part of the ObjectMonitor tagging mechanism. When we combine an
241 // ObjectMonitor reference with an offset, we need to remove the tag
242 // value in order to generate the proper address.
243 //
244 // We can either adjust the ObjectMonitor reference and then add the
245 // offset or we can adjust the offset that is added to the ObjectMonitor
246 // reference. The latter avoids an AGI (Address Generation Interlock)
247 // stall so the helper macro adjusts the offset value that is returned
248 // to the ObjectMonitor reference manipulation code:
249 //
250 #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
251 ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value)
252
253 markWord header() const;
254 volatile markWord* header_addr();
255 void set_header(markWord hdr);
256
257 intptr_t is_busy() const {
258 // TODO-FIXME: assert _owner == null implies _recursions = 0
259 // We do not include _ref_count in the is_busy() check because
260 // _ref_count is for indicating that the ObjectMonitor* is in
261 // use which is orthogonal to whether the ObjectMonitor itself
262 // is in use for a locking operation.
263 intptr_t ret_code = _contentions | _waiters | intptr_t(_cxq) | intptr_t(_EntryList);
264 if (!AsyncDeflateIdleMonitors) {
265 ret_code |= intptr_t(_owner);
266 } else {
267 if (_owner != DEFLATER_MARKER) {
268 ret_code |= intptr_t(_owner);
269 }
270 }
271 return ret_code;
272 }
273 const char* is_busy_to_string(stringStream* ss);
274
275 intptr_t is_entered(Thread* current) const;
276
277 void* owner() const; // Returns NULL if DEFLATER_MARKER is observed.
278 // Returns true if owner field == DEFLATER_MARKER and false otherwise.
279 bool owner_is_DEFLATER_MARKER();
280 void set_owner(void* owner);
281
282 jint waiters() const;
283
284 jint contentions() const;
285 intptr_t recursions() const { return _recursions; }
286
287 // JVM/TI GetObjectMonitorUsage() needs this:
288 ObjectWaiter* first_waiter() { return _WaitSet; }
289 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
290 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
291
292 protected:
293 // We don't typically expect or want the ctors or dtors to run.
294 // normal ObjectMonitors are type-stable and immortal.
295 ObjectMonitor() { ::memset((void*)this, 0, sizeof(*this)); }
296
297 ~ObjectMonitor() {
298 // TODO: Add asserts ...
299 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
300 // _contentions == 0 _EntryList == NULL etc
301 }
302
303 private:
304 void Recycle() {
305 // TODO: add stronger asserts ...
306 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
307 // _contentions == 0 EntryList == NULL
308 // _recursions == 0 _WaitSet == NULL
309 DEBUG_ONLY(stringStream ss;)
310 assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, "
311 "recursions=" INTPTR_FORMAT, is_busy_to_string(&ss), _recursions);
312 _succ = NULL;
313 _EntryList = NULL;
314 _cxq = NULL;
315 _WaitSet = NULL;
316 _recursions = 0;
317 }
318
319 public:
320
321 void* object() const;
322 void* object_addr();
323 void set_object(void* obj);
324 void set_allocation_state(AllocationState s);
325 AllocationState allocation_state() const;
326 bool is_free() const;
327 bool is_active() const;
328 bool is_old() const;
329 bool is_new() const;
330 void dec_ref_count();
331 void inc_ref_count();
332 jint ref_count() const;
333
334 // Returns true if the specified thread owns the ObjectMonitor. Otherwise
335 // returns false and throws IllegalMonitorStateException (IMSE).
336 bool check_owner(Thread* THREAD);
337 void clear();
338 void clear_using_JT();
339
340 void enter(TRAPS);
341 void exit(bool not_suspended, TRAPS);
342 void wait(jlong millis, bool interruptable, TRAPS);
343 void notify(TRAPS);
344 void notifyAll(TRAPS);
345
346 void print() const;
347 void print_on(outputStream* st) const;
348
349 // Use the following at your own risk
350 intptr_t complete_exit(TRAPS);
351 void reenter(intptr_t recursions, TRAPS);
352
353 private:
354 void AddWaiter(ObjectWaiter* waiter);
355 void INotify(Thread* self);
356 ObjectWaiter* DequeueWaiter();
357 void DequeueSpecificWaiter(ObjectWaiter* waiter);
358 void EnterI(TRAPS);
359 void ReenterI(Thread* self, ObjectWaiter* self_node);
360 void UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node);
361 int TryLock(Thread* self);
362 int NotRunnable(Thread* self, Thread* Owner);
363 int TrySpin(Thread* self);
364 void ExitEpilog(Thread* self, ObjectWaiter* Wakee);
365 bool ExitSuspendEquivalent(JavaThread* self);
366 void install_displaced_markword_in_object(const oop obj);
367 };
368
369 // A helper object for managing an ObjectMonitor*'s ref_count. There
370 // are special safety considerations when async deflation is used.
371 class ObjectMonitorHandle : public StackObj {
372 private:
373 ObjectMonitor* _om_ptr;
374 public:
375 ObjectMonitorHandle() { _om_ptr = NULL; }
376 ~ObjectMonitorHandle();
377
378 ObjectMonitor* om_ptr() const { return _om_ptr; }
379 // Save the ObjectMonitor* associated with the specified markWord and
380 // increment the ref_count.
381 bool save_om_ptr(oop object, markWord mark);
382
383 // For internal used by ObjectSynchronizer::monitors_iterate().
384 ObjectMonitorHandle(ObjectMonitor* _om_ptr);
385 // For internal use by ObjectSynchronizer::inflate().
386 void set_om_ptr(ObjectMonitor* om_ptr);
387 };
388
389 // Macro to use guarantee() for more strict AsyncDeflateIdleMonitors
390 // checks and assert() otherwise.
391 #define ADIM_guarantee(p, ...) \
392 do { \
393 if (AsyncDeflateIdleMonitors) { \
394 guarantee(p, __VA_ARGS__); \
395 } else { \
396 assert(p, __VA_ARGS__); \
397 } \
398 } while (0)
399
400 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP