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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 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 #include "utilities/checkedCast.hpp"
 34 
 35 class ObjectMonitor;
 36 class ParkEvent;
 37 
 38 // ObjectWaiter serves as a "proxy" or surrogate thread.
 39 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
 40 // ParkEvent instead.  Beware, however, that the JVMTI code
 41 // knows about ObjectWaiters, so we'll have to reconcile that code.
 42 // See next_waiter(), first_waiter(), etc.
 43 
 44 class ObjectWaiter : public StackObj {
 45  public:
 46   enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
 47   ObjectWaiter* volatile _next;
 48   ObjectWaiter* volatile _prev;
 49   JavaThread*   _thread;
 50   uint64_t      _notifier_tid;
 51   ParkEvent *   _event;
 52   volatile int  _notified;
 53   volatile TStates TState;
 54   bool          _active;           // Contention monitoring is enabled
 55  public:
 56   ObjectWaiter(JavaThread* current);
 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 // ObjectMonitor Layout Overview/Highlights/Restrictions:
 71 //
 72 // - The _header field must be at offset 0 because the displaced header
 73 //   from markWord is stored there. We do not want markWord.hpp to include
 74 //   ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
 75 //   means that ObjectMonitor cannot inherit from any other class nor can
 76 //   it use any virtual member functions. This restriction is critical to
 77 //   the proper functioning of the VM.
 78 // - The _header and _owner fields should be separated by enough space
 79 //   to avoid false sharing due to parallel access by different threads.
 80 //   This is an advisory recommendation.
 81 // - The general layout of the fields in ObjectMonitor is:
 82 //     _header
 83 //     <lightly_used_fields>
 84 //     <optional padding>
 85 //     _owner
 86 //     <remaining_fields>
 87 // - The VM assumes write ordering and machine word alignment with
 88 //   respect to the _owner field and the <remaining_fields> that can
 89 //   be read in parallel by other threads.
 90 // - Generally fields that are accessed closely together in time should
 91 //   be placed proximally in space to promote data cache locality. That
 92 //   is, temporal locality should condition spatial locality.
 93 // - We have to balance avoiding false sharing with excessive invalidation
 94 //   from coherence traffic. As such, we try to cluster fields that tend
 95 //   to be _written_ at approximately the same time onto the same data
 96 //   cache line.
 97 // - We also have to balance the natural tension between minimizing
 98 //   single threaded capacity misses with excessive multi-threaded
 99 //   coherency misses. There is no single optimal layout for both
100 //   single-threaded and multi-threaded environments.
101 //
102 // - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
103 //   enforced.
104 // - Adjacent ObjectMonitors should be separated by enough space to avoid
105 //   false sharing. This is handled by the ObjectMonitor allocation code
106 //   in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.
107 //
108 // Futures notes:
109 //   - Separating _owner from the <remaining_fields> by enough space to
110 //     avoid false sharing might be profitable. Given
111 //     http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
112 //     we know that the CAS in monitorenter will invalidate the line
113 //     underlying _owner. We want to avoid an L1 data cache miss on that
114 //     same line for monitorexit. Putting these <remaining_fields>:
115 //     _recursions, _EntryList, _cxq, and _succ, all of which may be
116 //     fetched in the inflated unlock path, on a different cache line
117 //     would make them immune to CAS-based invalidation from the _owner
118 //     field.
119 //
120 //   - The _recursions field should be of type int, or int32_t but not
121 //     intptr_t. There's no reason to use a 64-bit type for this field
122 //     in a 64-bit JVM.
123 
124 #define OM_CACHE_LINE_SIZE DEFAULT_CACHE_LINE_SIZE
125 
126 class ObjectMonitor : public CHeapObj<mtObjectMonitor> {
127   friend class ObjectSynchronizer;
128   friend class ObjectWaiter;
129   friend class VMStructs;
130   JVMCI_ONLY(friend class JVMCIVMStructs;)
131 
132   static OopStorage* _oop_storage;
133 
134   // The sync code expects the header field to be at offset zero (0).
135   // Enforced by the assert() in header_addr().
136   volatile markWord _header;        // displaced object header word - mark
137   WeakHandle _object;               // backward object pointer
138   // Separate _header and _owner on different cache lines since both can
139   // have busy multi-threaded access. _header and _object are set at initial
140   // inflation. The _object does not change, so it is a good choice to share
141   // its cache line with _header.
142   DEFINE_PAD_MINUS_SIZE(0, OM_CACHE_LINE_SIZE, sizeof(volatile markWord) +
143                         sizeof(WeakHandle));
144   // Used by async deflation as a marker in the _owner field.
145   // Note that the choice of the two markers is peculiar:
146   // - They need to represent values that cannot be pointers. In particular,
147   //   we achieve this by using the lowest two bits.
148   // - ANONYMOUS_OWNER should be a small value, it is used in generated code
149   //   and small values encode much better.
150   // - We test for anonymous owner by testing for the lowest bit, therefore
151   //   DEFLATER_MARKER must *not* have that bit set.
152   #define DEFLATER_MARKER reinterpret_cast<void*>(2)
153 public:
154   // NOTE: Typed as uintptr_t so that we can pick it up in SA, via vmStructs.
155   static const uintptr_t ANONYMOUS_OWNER = 1;
156 
157 private:
158   static void* anon_owner_ptr() { return reinterpret_cast<void*>(ANONYMOUS_OWNER); }
159 
160   void* volatile _owner;            // pointer to owning thread OR BasicLock
161   volatile uint64_t _previous_owner_tid;  // thread id of the previous owner of the monitor
162   // Separate _owner and _next_om on different cache lines since
163   // both can have busy multi-threaded access. _previous_owner_tid is only
164   // changed by ObjectMonitor::exit() so it is a good choice to share the
165   // cache line with _owner.
166   DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(void* volatile) +
167                         sizeof(volatile uint64_t));
168   ObjectMonitor* _next_om;          // Next ObjectMonitor* linkage
169   volatile intx _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 
174   ObjectWaiter* volatile _cxq;      // LL of recently-arrived threads blocked on entry.
175   JavaThread* volatile _succ;       // Heir presumptive thread - used for futile wakeup throttling
176   JavaThread* volatile _Responsible;
177 
178   volatile int _Spinner;            // for exit->spinner handoff optimization
179   volatile int _SpinDuration;
180 
181   int _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. It is also used by the async deflation protocol. See
184                                     // ObjectMonitor::deflate_monitor().
185  protected:
186   ObjectWaiter* volatile _WaitSet;  // LL of threads wait()ing on the monitor
187   volatile int  _waiters;           // number of waiting threads
188  private:
189   volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
190 
191  public:
192 
193   static void Initialize();
194 
195   // Only perform a PerfData operation if the PerfData object has been
196   // allocated and if the PerfDataManager has not freed the PerfData
197   // objects which can happen at normal VM shutdown.
198   //
199   #define OM_PERFDATA_OP(f, op_str)                 \
200     do {                                            \
201       if (ObjectMonitor::_sync_ ## f != nullptr &&  \
202           PerfDataManager::has_PerfData()) {        \
203         ObjectMonitor::_sync_ ## f->op_str;         \
204       }                                             \
205     } while (0)
206 
207   static PerfCounter * _sync_ContendedLockAttempts;
208   static PerfCounter * _sync_FutileWakeups;
209   static PerfCounter * _sync_Parks;
210   static PerfCounter * _sync_Notifications;
211   static PerfCounter * _sync_Inflations;
212   static PerfCounter * _sync_Deflations;
213   static PerfLongVariable * _sync_MonExtant;
214 
215   static int Knob_SpinLimit;
216 
217   static ByteSize owner_offset()       { return byte_offset_of(ObjectMonitor, _owner); }
218   static ByteSize recursions_offset()  { return byte_offset_of(ObjectMonitor, _recursions); }
219   static ByteSize cxq_offset()         { return byte_offset_of(ObjectMonitor, _cxq); }
220   static ByteSize succ_offset()        { return byte_offset_of(ObjectMonitor, _succ); }
221   static ByteSize EntryList_offset()   { return byte_offset_of(ObjectMonitor, _EntryList); }
222 
223   // ObjectMonitor references can be ORed with markWord::monitor_value
224   // as part of the ObjectMonitor tagging mechanism. When we combine an
225   // ObjectMonitor reference with an offset, we need to remove the tag
226   // value in order to generate the proper address.
227   //
228   // We can either adjust the ObjectMonitor reference and then add the
229   // offset or we can adjust the offset that is added to the ObjectMonitor
230   // reference. The latter avoids an AGI (Address Generation Interlock)
231   // stall so the helper macro adjusts the offset value that is returned
232   // to the ObjectMonitor reference manipulation code:
233   //
234   #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
235     ((in_bytes(ObjectMonitor::f ## _offset())) - checked_cast<int>(markWord::monitor_value))
236 
237   markWord           header() const;
238   volatile markWord* header_addr();
239   void               set_header(markWord hdr);
240 
241   bool is_busy() const {
242     // TODO-FIXME: assert _owner == null implies _recursions = 0
243     intptr_t ret_code = intptr_t(_waiters) | intptr_t(_cxq) | intptr_t(_EntryList);
244     int cnts = contentions(); // read once
245     if (cnts > 0) {
246       ret_code |= intptr_t(cnts);
247     }
248     if (!owner_is_DEFLATER_MARKER()) {
249       ret_code |= intptr_t(owner_raw());
250     }
251     return ret_code != 0;
252   }
253   const char* is_busy_to_string(stringStream* ss);
254 
255   bool is_entered(JavaThread* current) const;
256 
257   // Returns true if this OM has an owner, false otherwise.
258   bool      has_owner() const;
259   void*     owner() const;  // Returns null if DEFLATER_MARKER is observed.
260   void*     owner_raw() const;
261   // Returns true if owner field == DEFLATER_MARKER and false otherwise.
262   bool      owner_is_DEFLATER_MARKER() const;
263   // Returns true if 'this' is being async deflated and false otherwise.
264   bool      is_being_async_deflated();
265   // Clear _owner field; current value must match old_value.
266   void      release_clear_owner(void* old_value);
267   // Simply set _owner field to new_value; current value must match old_value.
268   void      set_owner_from(void* old_value, void* new_value);
269   // Simply set _owner field to current; current value must match basic_lock_p.
270   void      set_owner_from_BasicLock(void* basic_lock_p, JavaThread* current);
271   // Try to set _owner field to new_value if the current value matches
272   // old_value, using Atomic::cmpxchg(). Otherwise, does not change the
273   // _owner field. Returns the prior value of the _owner field.
274   void*     try_set_owner_from(void* old_value, void* new_value);
275 
276   void set_owner_anonymous() {
277     set_owner_from(nullptr, anon_owner_ptr());
278   }
279 
280   bool is_owner_anonymous() const {
281     return owner_raw() == anon_owner_ptr();
282   }
283 
284   void set_owner_from_anonymous(Thread* owner) {
285     set_owner_from(anon_owner_ptr(), owner);
286   }
287 
288   // Simply get _next_om field.
289   ObjectMonitor* next_om() const;
290   // Simply set _next_om field to new_value.
291   void set_next_om(ObjectMonitor* new_value);
292 
293   int       waiters() const;
294 
295   int       contentions() const;
296   void      add_to_contentions(int value);
297   intx      recursions() const                                         { return _recursions; }
298   void      set_recursions(size_t recursions);
299 
300   // JVM/TI GetObjectMonitorUsage() needs this:
301   ObjectWaiter* first_waiter()                                         { return _WaitSet; }
302   ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
303   JavaThread* thread_of_waiter(ObjectWaiter* o)                        { return o->_thread; }
304 
305   ObjectMonitor(oop object);
306   ~ObjectMonitor();
307 
308   oop       object() const;
309   oop       object_peek() const;
310 
311   // Returns true if the specified thread owns the ObjectMonitor. Otherwise
312   // returns false and throws IllegalMonitorStateException (IMSE).
313   bool      check_owner(TRAPS);
314 
315  private:
316   class ExitOnSuspend {
317    protected:
318     ObjectMonitor* _om;
319     bool _om_exited;
320    public:
321     ExitOnSuspend(ObjectMonitor* om) : _om(om), _om_exited(false) {}
322     void operator()(JavaThread* current);
323     bool exited() { return _om_exited; }
324   };
325   class ClearSuccOnSuspend {
326    protected:
327     ObjectMonitor* _om;
328    public:
329     ClearSuccOnSuspend(ObjectMonitor* om) : _om(om)  {}
330     void operator()(JavaThread* current);
331   };
332  public:
333   bool      enter_for(JavaThread* locking_thread);
334   bool      enter(JavaThread* current);
335   void      exit(JavaThread* current, bool not_suspended = true);
336   void      wait(jlong millis, bool interruptible, TRAPS);
337   void      notify(TRAPS);
338   void      notifyAll(TRAPS);
339 
340   void      print() const;
341 #ifdef ASSERT
342   void      print_debug_style_on(outputStream* st) const;
343 #endif
344   void      print_on(outputStream* st) const;
345 
346   // Use the following at your own risk
347   intx      complete_exit(JavaThread* current);
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       TrySpin(JavaThread* current);
359   void      ExitEpilog(JavaThread* current, ObjectWaiter* Wakee);
360 
361   // Deflation support
362   bool      deflate_monitor();
363   void      install_displaced_markword_in_object(const oop obj);
364 };
365 
366 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP