1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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
34class 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
42class 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
128class 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 JVMCI_ONLY(friend class JVMCIVMStructs;)
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 void * volatile _owner; // pointer to owning thread OR BasicLock
154 volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
155 volatile intptr_t _recursions; // recursion count, 0 for first entry
156 ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry.
157 // The list is actually composed of WaitNodes,
158 // acting as proxies for Threads.
159 private:
160 ObjectWaiter * volatile _cxq; // LL of recently-arrived threads blocked on entry.
161 Thread * volatile _succ; // Heir presumptive thread - used for futile wakeup throttling
162 Thread * volatile _Responsible;
163
164 volatile int _Spinner; // for exit->spinner handoff optimization
165 volatile int _SpinDuration;
166
167 volatile jint _contentions; // Number of active contentions in enter(). It is used by is_busy()
168 // along with other fields to determine if an ObjectMonitor can be
169 // deflated. See ObjectSynchronizer::deflate_monitor().
170 protected:
171 ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
172 volatile jint _waiters; // number of waiting threads
173 private:
174 volatile int _WaitSetLock; // protects Wait Queue - simple spinlock
175
176 public:
177 static void Initialize();
178
179 // Only perform a PerfData operation if the PerfData object has been
180 // allocated and if the PerfDataManager has not freed the PerfData
181 // objects which can happen at normal VM shutdown.
182 //
183 #define OM_PERFDATA_OP(f, op_str) \
184 do { \
185 if (ObjectMonitor::_sync_ ## f != NULL && \
186 PerfDataManager::has_PerfData()) { \
187 ObjectMonitor::_sync_ ## f->op_str; \
188 } \
189 } while (0)
190
191 static PerfCounter * _sync_ContendedLockAttempts;
192 static PerfCounter * _sync_FutileWakeups;
193 static PerfCounter * _sync_Parks;
194 static PerfCounter * _sync_Notifications;
195 static PerfCounter * _sync_Inflations;
196 static PerfCounter * _sync_Deflations;
197 static PerfLongVariable * _sync_MonExtant;
198
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 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 markOopDesc::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()) - markOopDesc::monitor_value)
229
230 markOop header() const;
231 volatile markOop* header_addr();
232 void set_header(markOop hdr);
233
234 intptr_t is_busy() const {
235 // TODO-FIXME: assert _owner == null implies _recursions = 0
236 return _contentions|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
237 }
238 const char* is_busy_to_string(stringStream* ss);
239
240 intptr_t is_entered(Thread* current) const;
241
242 void* owner() const;
243 void set_owner(void* owner);
244
245 jint waiters() const;
246
247 jint contentions() const;
248 intptr_t recursions() const { return _recursions; }
249
250 // JVM/TI GetObjectMonitorUsage() needs this:
251 ObjectWaiter* first_waiter() { return _WaitSet; }
252 ObjectWaiter* next_waiter(ObjectWaiter* o) { return o->_next; }
253 Thread* thread_of_waiter(ObjectWaiter* o) { return o->_thread; }
254
255 protected:
256 // We don't typically expect or want the ctors or dtors to run.
257 // normal ObjectMonitors are type-stable and immortal.
258 ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); }
259
260 ~ObjectMonitor() {
261 // TODO: Add asserts ...
262 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
263 // _contentions == 0 _EntryList == NULL etc
264 }
265
266 private:
267 void Recycle() {
268 // TODO: add stronger asserts ...
269 // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
270 // _contentions == 0 EntryList == NULL
271 // _recursions == 0 _WaitSet == NULL
272 DEBUG_ONLY(stringStream ss;)
273 assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, "
274 "recursions=" INTPTR_FORMAT, is_busy_to_string(&ss), _recursions);
275 _succ = NULL;
276 _EntryList = NULL;
277 _cxq = NULL;
278 _WaitSet = NULL;
279 _recursions = 0;
280 }
281
282 public:
283
284 void* object() const;
285 void* object_addr();
286 void set_object(void* obj);
287
288 bool check(TRAPS); // true if the thread owns the monitor.
289 void check_slow(TRAPS);
290 void clear();
291
292 void enter(TRAPS);
293 void exit(bool not_suspended, TRAPS);
294 void wait(jlong millis, bool interruptable, TRAPS);
295 void notify(TRAPS);
296 void notifyAll(TRAPS);
297
298 void print() const;
299 void print_on(outputStream* st) const;
300
301// Use the following at your own risk
302 intptr_t complete_exit(TRAPS);
303 void reenter(intptr_t recursions, TRAPS);
304
305 private:
306 void AddWaiter(ObjectWaiter * waiter);
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_RUNTIME_OBJECTMONITOR_HPP
321