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
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
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  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  *
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 18  *
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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/perfDataTypes.hpp"
 33 
 34 class ObjectMonitor;
 35 class ParkEvent;
 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   ObjectWaiter* volatile _next;
 47   ObjectWaiter* volatile _prev;
 48   JavaThread*   _thread;
 49   uint64_t      _notifier_tid;
 50   ParkEvent *   _event;
 51   volatile int  _notified;
 52   volatile TStates TState;
 53   bool          _active;           // Contention monitoring is enabled
 54  public:
 55   ObjectWaiter(JavaThread* current);
 56 
 57   void wait_reenter_begin(ObjectMonitor *mon);
 58   void wait_reenter_end(ObjectMonitor *mon);
 59 };
 60 
 61 // The ObjectMonitor class implements the heavyweight version of a
 62 // JavaMonitor. The lightweight fast-lock version has been
 63 // inflated into an ObjectMonitor. This inflation is typically due to
 64 // contention or use of Object.wait().
 65 //
 66 // WARNING: This is a very sensitive and fragile class. DO NOT make any
 67 // changes unless you are fully aware of the underlying semantics.
 68 //
 69 // ObjectMonitor Layout Overview/Highlights/Restrictions:
 70 //
 71 // - The _header field must be at offset 0 because the displaced header
 72 //   from markWord is stored there. We do not want markWord.hpp to include
 73 //   ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
 74 //   means that ObjectMonitor cannot inherit from any other class nor can
 75 //   it use any virtual member functions. This restriction is critical to
 76 //   the proper functioning of the VM.
 77 // - The _header and _owner fields should be separated by enough space
 78 //   to avoid false sharing due to parallel access by different threads.
 79 //   This is an advisory recommendation.
 80 // - The general layout of the fields in ObjectMonitor is:
 81 //     _header
 82 //     <lightly_used_fields>
 83 //     <optional padding>
 84 //     _owner
 85 //     <remaining_fields>
 86 // - The VM assumes write ordering and machine word alignment with
 87 //   respect to the _owner field and the <remaining_fields> that can
 88 //   be read in parallel by other threads.
 89 // - Generally fields that are accessed closely together in time should
 90 //   be placed proximally in space to promote data cache locality. That
 91 //   is, temporal locality should condition spatial locality.
 92 // - We have to balance avoiding false sharing with excessive invalidation
 93 //   from coherence traffic. As such, we try to cluster fields that tend
 94 //   to be _written_ at approximately the same time onto the same data
 95 //   cache line.
 96 // - We also have to balance the natural tension between minimizing
 97 //   single threaded capacity misses with excessive multi-threaded
 98 //   coherency misses. There is no single optimal layout for both
 99 //   single-threaded and multi-threaded environments.
100 //
101 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
102 //   enforced.
103 // - Adjacent ObjectMonitors should be separated by enough space to avoid
104 //   false sharing. This is handled by the ObjectMonitor allocation code
105 //   in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
106 //
107 // Futures notes:
108 //   - Separating _owner from the <remaining_fields> by enough space to
109 //     avoid false sharing might be profitable. Given
110 //     http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
111 //     we know that the CAS in monitorenter will invalidate the line
112 //     underlying _owner. We want to avoid an L1 data cache miss on that
113 //     same line for monitorexit. Putting these <remaining_fields>:
114 //     _recursions, _EntryList, _cxq, and _succ, all of which may be
115 //     fetched in the inflated unlock path, on a different cache line
116 //     would make them immune to CAS-based invalidation from the _owner
117 //     field.
118 //
119 //   - The _recursions field should be of type int, or int32_t but not
120 //     intptr_t. There's no reason to use a 64-bit type for this field
121 //     in a 64-bit JVM.
122 
123 #ifndef OM_CACHE_LINE_SIZE
124 // Use DEFAULT_CACHE_LINE_SIZE if not already specified for
125 // the current build platform.
126 #define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE
127 #endif
128 
129 class ObjectMonitor : public CHeapObj<mtObjectMonitor> {
130   friend class ObjectSynchronizer;
131   friend class ObjectWaiter;
132   friend class VMStructs;
133   JVMCI_ONLY(friend class JVMCIVMStructs;)
134 
135   static OopStorage* _oop_storage;
136 
137   // The sync code expects the header field to be at offset zero (0).
138   // Enforced by the assert() in header_addr().
139   volatile markWord _header;        // displaced object header word - mark
140   WeakHandle _object;               // backward object pointer
141   // Separate _header and _owner on different cache lines since both can
142   // have busy multi-threaded access. _header and _object are set at initial
143   // inflation. The _object does not change, so it is a good choice to share
144   // its cache line with _header.
145   DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
146                         sizeof(WeakHandle));
147   // Used by async deflation as a marker in the _owner field:
148   #define DEFLATER_MARKER reinterpret_cast<void*>(-1)
149   #define ANONYMOUS_OWNER reinterpret_cast<void*>(1)
150   void* volatile _owner;            // pointer to owning thread
151   volatile uint64_t _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 uint64_t));
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   int _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 int  _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 = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList);
237     int cnts = contentions(); // read once
238     if (cnts > 0) {
239       ret_code |= intptr_t(cnts);
240     }
241     if (!owner_is_DEFLATER_MARKER()) {
242       ret_code |= intptr_t(owner_raw());
243     }
244     return ret_code != 0;
245   }
246   const char* is_busy_to_string(stringStream* ss);
247 
248   intptr_t  is_entered(JavaThread* current) const;
249 
250   void*     owner() const;  // Returns NULL if DEFLATER_MARKER is observed.
251   void*     owner_raw() const;
252   // Returns true if owner field == DEFLATER_MARKER and false otherwise.
253   bool      owner_is_DEFLATER_MARKER() const;
254   // Returns true if 'this' is being async deflated and false otherwise.
255   bool      is_being_async_deflated();
256   // Clear _owner field; current value must match old_value.
257   void      release_clear_owner(void* old_value);
258   // Simply set _owner field to new_value; current value must match old_value.
259   void      set_owner_from(void* old_value, void* new_value);
260   // Try to set _owner field to new_value if the current value matches
261   // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
262   // _owner field. Returns the prior value of the _owner field.
263   void*     try_set_owner_from(void* old_value, void* new_value);
264 
265   // Simply get _next_om field.
266   ObjectMonitor* next_om() const;
267   // Get _next_om field with acquire semantics.
268   ObjectMonitor* next_om_acquire() const;
269   // Simply set _next_om field to new_value.
270   void set_next_om(ObjectMonitor* new_value);
271   // Set _next_om field to new_value with release semantics.
272   void release_set_next_om(ObjectMonitor* new_value);
273   // Try to set _next_om field to new_value if the current value matches
274   // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
275   // _next_om field. Returns the prior value of the _next_om field.
276   ObjectMonitor* try_set_next_om(ObjectMonitor* old_value, ObjectMonitor* new_value);
277 
278   void set_owner_anonymous() {
279     set_owner_from(NULL, ANONYMOUS_OWNER);
280   }
281 
282   bool is_owner_anonymous() const {
283     return _owner == ANONYMOUS_OWNER;
284   }
285 
286   void set_owner_from_anonymous(Thread* owner) {
287     set_owner_from(ANONYMOUS_OWNER, owner);
288   }
289 
290   int       waiters() const;
291 
292   int       contentions() const;
293   void      add_to_contentions(int value);
294   intx      recursions() const                                         { return _recursions; }
295 
296   // JVM/TI GetObjectMonitorUsage() needs this:
297   ObjectWaiter* first_waiter()                                         { return _WaitSet; }
298   ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
299   JavaThread* thread_of_waiter(ObjectWaiter* o)                        { return o->_thread; }
300 
301   ObjectMonitor(oop object);
302   ~ObjectMonitor();
303 
304   oop       object() const;
305   oop       object_peek() const;
306 
307   // Returns true if the specified thread owns the ObjectMonitor. Otherwise
308   // returns false and throws IllegalMonitorStateException (IMSE).
309   bool      check_owner(TRAPS);
310 
311  private:
312   class ExitOnSuspend {
313    protected:
314     ObjectMonitor* _om;
315     bool _om_exited;
316    public:
317     ExitOnSuspend(ObjectMonitor* om) : _om(om), _om_exited(false) {}
318     void operator()(JavaThread* current);
319     bool exited() { return _om_exited; }
320   };
321   class ClearSuccOnSuspend {
322    protected:
323     ObjectMonitor* _om;
324    public:
325     ClearSuccOnSuspend(ObjectMonitor* om) : _om(om)  {}
326     void operator()(JavaThread* current);
327   };
328  public:
329   bool      enter(JavaThread* current);
330   void      exit(JavaThread* current, bool not_suspended = true);
331   void      wait(jlong millis, bool interruptible, TRAPS);
332   void      notify(TRAPS);
333   void      notifyAll(TRAPS);
334 
335   void      print() const;
336 #ifdef ASSERT
337   void      print_debug_style_on(outputStream* st) const;
338 #endif
339   void      print_on(outputStream* st) const;
340 
341   // Use the following at your own risk
342   intx      complete_exit(JavaThread* current);
343   bool      reenter(intx recursions, JavaThread* current);
344 
345   static void maybe_deflate_dead(oop* p);
346 
347  private:
348   void      AddWaiter(ObjectWaiter* waiter);
349   void      INotify(JavaThread* current);
350   ObjectWaiter* DequeueWaiter();
351   void      DequeueSpecificWaiter(ObjectWaiter* waiter);
352   void      EnterI(JavaThread* current);
353   void      ReenterI(JavaThread* current, ObjectWaiter* current_node);
354   void      UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* current_node);
355   int       TryLock(JavaThread* current);
356   int       NotRunnable(JavaThread* current, JavaThread* Owner);
357   int       TrySpin(JavaThread* current);
358   void      ExitEpilog(JavaThread* current, ObjectWaiter* Wakee);
359 
360   // Deflation support
361   bool      deflate_monitor();
362   void      install_displaced_markword_in_object(const oop obj);
363 };
364 
365 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP