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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 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 BasicLock/stack 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   // Note that the choice of the two markers is peculiar:
149   // - They need to represent values that cannot be pointers. In particular,
150   //   we achieve this by using the lowest two bits
151   // - ANONYMOUS_OWNER should be a small value, it is used in generated code
152   //   and small values encode much better
153   // - We test for anonymous owner by testing for the lowest bit, therefore
154   //   DEFLATER_MARKER must *not* have that bit set.
155   #define DEFLATER_MARKER reinterpret_cast<void*>(2)
156   #define ANONYMOUS_OWNER reinterpret_cast<void*>(1)
157   void* volatile _owner;            // pointer to owning thread OR BasicLock
158   volatile uint64_t _previous_owner_tid;  // thread id of the previous owner of the monitor
159   // Separate _owner and _next_om on different cache lines since
160   // both can have busy multi-threaded access. _previous_owner_tid is only
161   // changed by ObjectMonitor::exit() so it is a good choice to share the
162   // cache line with _owner.
163   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
164                         sizeof(volatile uint64_t));
165   ObjectMonitor* _next_om;          // Next ObjectMonitor* linkage
166   volatile intx _recursions;        // recursion count, 0 for first entry
167   ObjectWaiter* volatile _EntryList;  // Threads blocked on entry or reentry.
168                                       // The list is actually composed of WaitNodes,
169                                       // acting as proxies for Threads.
170 
171   ObjectWaiter* volatile _cxq;      // LL of recently-arrived threads blocked on entry.
172   JavaThread* volatile _succ;       // Heir presumptive thread - used for futile wakeup throttling
173   JavaThread* volatile _Responsible;
174 
175   volatile int _Spinner;            // for exit->spinner handoff optimization
176   volatile int _SpinDuration;
177 
178   int _contentions;                 // Number of active contentions in enter(). It is used by is_busy()
179                                     // along with other fields to determine if an ObjectMonitor can be
180                                     // deflated. It is also used by the async deflation protocol. See
181                                     // ObjectMonitor::deflate_monitor().
182  protected:
183   ObjectWaiter* volatile _WaitSet;  // LL of threads wait()ing on the monitor
184   volatile int  _waiters;           // number of waiting threads
185  private:
186   volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
187 
188  public:
189   static void Initialize();
190 
191   // Only perform a PerfData operation if the PerfData object has been
192   // allocated and if the PerfDataManager has not freed the PerfData
193   // objects which can happen at normal VM shutdown.
194   //
195   #define OM_PERFDATA_OP(f, op_str)                 \
196     do {                                            \
197       if (ObjectMonitor::_sync_ ## f != nullptr &&  \
198           PerfDataManager::has_PerfData()) {        \
199         ObjectMonitor::_sync_ ## f->op_str;         \
200       }                                             \
201     } while (0)
202 
203   static PerfCounter * _sync_ContendedLockAttempts;
204   static PerfCounter * _sync_FutileWakeups;
205   static PerfCounter * _sync_Parks;
206   static PerfCounter * _sync_Notifications;
207   static PerfCounter * _sync_Inflations;
208   static PerfCounter * _sync_Deflations;
209   static PerfLongVariable * _sync_MonExtant;
210 
211   static int Knob_SpinLimit;
212 
213   // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
214   // ByteSize would also be an appropriate type.
215   static int header_offset_in_bytes()      { return offset_of(ObjectMonitor, _header); }
216   static int owner_offset_in_bytes()       { return offset_of(ObjectMonitor, _owner); }
217   static int recursions_offset_in_bytes()  { return offset_of(ObjectMonitor, _recursions); }
218   static int cxq_offset_in_bytes()         { return offset_of(ObjectMonitor, _cxq); }
219   static int succ_offset_in_bytes()        { return offset_of(ObjectMonitor, _succ); }
220   static int EntryList_offset_in_bytes()   { return offset_of(ObjectMonitor, _EntryList); }
221 
222   // ObjectMonitor references can be ORed with markWord::monitor_value
223   // as part of the ObjectMonitor tagging mechanism. When we combine an
224   // ObjectMonitor reference with an offset, we need to remove the tag
225   // value in order to generate the proper address.
226   //
227   // We can either adjust the ObjectMonitor reference and then add the
228   // offset or we can adjust the offset that is added to the ObjectMonitor
229   // reference. The latter avoids an AGI (Address Generation Interlock)
230   // stall so the helper macro adjusts the offset value that is returned
231   // to the ObjectMonitor reference manipulation code:
232   //
233   #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
234     ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value)
235 
236   markWord           header() const;
237   volatile markWord* header_addr();
238   void               set_header(markWord hdr);
239 
240   bool is_busy() const {
241     // TODO-FIXME: assert _owner == null implies _recursions = 0
242     intptr_t ret_code = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList);
243     int cnts = contentions(); // read once
244     if (cnts > 0) {
245       ret_code |= intptr_t(cnts);
246     }
247     if (!owner_is_DEFLATER_MARKER()) {
248       ret_code |= intptr_t(owner_raw());
249     }
250     return ret_code != 0;
251   }
252   const char* is_busy_to_string(stringStream* ss);
253 
254   intptr_t  is_entered(JavaThread* current) const;
255 
256   // Returns true if this OM has an owner, false otherwise.
257   bool      has_owner() const;
258   void*     owner() const;  // Returns null if DEFLATER_MARKER is observed.
259   void*     owner_raw() const;
260   // Returns true if owner field == DEFLATER_MARKER and false otherwise.
261   bool      owner_is_DEFLATER_MARKER() const;
262   // Returns true if 'this' is being async deflated and false otherwise.
263   bool      is_being_async_deflated();
264   // Clear _owner field; current value must match old_value.
265   void      release_clear_owner(void* old_value);
266   // Simply set _owner field to new_value; current value must match old_value.
267   void      set_owner_from(void* old_value, void* new_value);
268   // Simply set _owner field to current; current value must match basic_lock_p.
269   void      set_owner_from_BasicLock(void* basic_lock_p, JavaThread* current);
270   // Try to set _owner field to new_value if the current value matches
271   // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
272   // _owner field. Returns the prior value of the _owner field.
273   void*     try_set_owner_from(void* old_value, void* new_value);
274 
275   void set_owner_anonymous() {
276     set_owner_from(NULL, ANONYMOUS_OWNER);
277   }
278 
279   bool is_owner_anonymous() const {
280     return owner_raw() == ANONYMOUS_OWNER;
281   }
282 
283   void set_owner_from_anonymous(Thread* owner) {
284     set_owner_from(ANONYMOUS_OWNER, owner);
285   }
286 
287   // Simply get _next_om field.
288   ObjectMonitor* next_om() const;
289   // Simply set _next_om field to new_value.
290   void set_next_om(ObjectMonitor* new_value);
291 
292   int       waiters() const;
293 
294   int       contentions() const;
295   void      add_to_contentions(int value);
296   intx      recursions() const                                         { return _recursions; }
297 
298   // JVM/TI GetObjectMonitorUsage() needs this:
299   ObjectWaiter* first_waiter()                                         { return _WaitSet; }
300   ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
301   JavaThread* thread_of_waiter(ObjectWaiter* o)                        { return o->_thread; }
302 
303   ObjectMonitor(oop object);
304   ~ObjectMonitor();
305 
306   oop       object() const;
307   oop       object_peek() const;
308 
309   // Returns true if the specified thread owns the ObjectMonitor. Otherwise
310   // returns false and throws IllegalMonitorStateException (IMSE).
311   bool      check_owner(TRAPS);
312 
313  private:
314   class ExitOnSuspend {
315    protected:
316     ObjectMonitor* _om;
317     bool _om_exited;
318    public:
319     ExitOnSuspend(ObjectMonitor* om) : _om(om), _om_exited(false) {}
320     void operator()(JavaThread* current);
321     bool exited() { return _om_exited; }
322   };
323   class ClearSuccOnSuspend {
324    protected:
325     ObjectMonitor* _om;
326    public:
327     ClearSuccOnSuspend(ObjectMonitor* om) : _om(om)  {}
328     void operator()(JavaThread* current);
329   };
330  public:
331   bool      enter(JavaThread* current);
332   void      exit(JavaThread* current, bool not_suspended = true);
333   void      wait(jlong millis, bool interruptible, TRAPS);
334   void      notify(TRAPS);
335   void      notifyAll(TRAPS);
336 
337   void      print() const;
338 #ifdef ASSERT
339   void      print_debug_style_on(outputStream* st) const;
340 #endif
341   void      print_on(outputStream* st) const;
342 
343   // Use the following at your own risk
344   intx      complete_exit(JavaThread* current);
345   bool      reenter(intx recursions, JavaThread* current);
346 
347   static void maybe_deflate_dead(oop* p);
348 
349  private:
350   void      AddWaiter(ObjectWaiter* waiter);
351   void      INotify(JavaThread* current);
352   ObjectWaiter* DequeueWaiter();
353   void      DequeueSpecificWaiter(ObjectWaiter* waiter);
354   void      EnterI(JavaThread* current);
355   void      ReenterI(JavaThread* current, ObjectWaiter* current_node);
356   void      UnlinkAfterAcquire(JavaThread* current, ObjectWaiter* current_node);
357   int       TryLock(JavaThread* current);
358   int       NotRunnable(JavaThread* current, JavaThread* Owner);
359   int       TrySpin(JavaThread* current);
360   void      ExitEpilog(JavaThread* current, ObjectWaiter* Wakee);
361 
362   // Deflation support
363   bool      deflate_monitor();
364   void      install_displaced_markword_in_object(const oop obj);
365 };
366 
367 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP