rev 12096 : 8166970: Adapt mutex padding according to DEFAULT_CACHE_LINE_SIZE
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   1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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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  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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  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
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  24 
  25 #ifndef SHARE_VM_RUNTIME_MUTEX_HPP
  26 #define SHARE_VM_RUNTIME_MUTEX_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "runtime/os.hpp"
  30 #include "utilities/histogram.hpp"
  31 
  32 // The SplitWord construct allows us to colocate the contention queue
  33 // (cxq) with the lock-byte.  The queue elements are ParkEvents, which are
  34 // always aligned on 256-byte addresses - the least significant byte of
  35 // a ParkEvent is always 0.  Colocating the lock-byte with the queue
  36 // allows us to easily avoid what would otherwise be a race in lock()
  37 // if we were to use two completely separate fields for the contention queue
  38 // and the lock indicator.  Specifically, colocation renders us immune
  39 // from the race where a thread might enqueue itself in the lock() slow-path
  40 // immediately after the lock holder drops the outer lock in the unlock()
  41 // fast-path.
  42 //
  43 // Colocation allows us to use a fast-path unlock() form that uses
  44 // A MEMBAR instead of a CAS.  MEMBAR has lower local latency than CAS
  45 // on many platforms.
  46 //
  47 // See:
  48 // +  http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
  49 // +  http://blogs.sun.com/dave/resource/synchronization-public2.pdf
  50 //
  51 // Note that we're *not* using word-tearing the classic sense.
  52 // The lock() fast-path will CAS the lockword and the unlock()
  53 // fast-path will store into the lock-byte colocated within the lockword.
  54 // We depend on the fact that all our reference platforms have
  55 // coherent and atomic byte accesses.  More precisely, byte stores
  56 // interoperate in a safe, sane, and expected manner with respect to
  57 // CAS, ST and LDs to the full-word containing the byte.
  58 // If you're porting HotSpot to a platform where that isn't the case
  59 // then you'll want change the unlock() fast path from:
  60 //    STB;MEMBAR #storeload; LDN
  61 // to a full-word CAS of the lockword.
  62 
  63 
  64 union SplitWord {   // full-word with separately addressable LSB
  65   volatile intptr_t FullWord ;
  66   volatile void * Address ;
  67   volatile jbyte Bytes [sizeof(intptr_t)] ;
  68 } ;
  69 
  70 // Endian-ness ... index of least-significant byte in SplitWord.Bytes[]
  71 #ifdef VM_LITTLE_ENDIAN
  72  #define _LSBINDEX 0
  73 #else
  74  #define _LSBINDEX (sizeof(intptr_t)-1)
  75 #endif
  76 
  77 class ParkEvent ;
  78 
  79 // See orderAccess.hpp.  We assume throughout the VM that mutex lock and
  80 // try_lock do fence-lock-acquire, and that unlock does a release-unlock,
  81 // *in that order*.  If their implementations change such that these
  82 // assumptions are violated, a whole lot of code will break.
  83 
  84 class MonitorBase : public CHeapObj<mtInternal> {




  85  public:
  86   // A special lock: Is a lock where you are guaranteed not to block while you are
  87   // holding it, i.e., no vm operation can happen, taking other locks, etc.
  88   // NOTE: It is critical that the rank 'special' be the lowest (earliest)
  89   // (except for "event"?) for the deadlock detection to work correctly.
  90   // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
  91   // which being external to the VM are not subject to deadlock detection.
  92   // The rank safepoint is used only for synchronization in reaching a
  93   // safepoint and leaving a safepoint.  It is only used for the Safepoint_lock
  94   // currently.  While at a safepoint no mutexes of rank safepoint are held
  95   // by any thread.
  96   // The rank named "leaf" is probably historical (and should
  97   // be changed) -- mutexes of this rank aren't really leaf mutexes
  98   // at all.
  99   enum lock_types {
 100        event,
 101        special,
 102        suspend_resume,
 103        leaf        = suspend_resume +   2,
 104        safepoint   = leaf           +  10,
 105        barrier     = safepoint      +   1,
 106        nonleaf     = barrier        +   1,
 107        max_nonleaf = nonleaf        + 900,
 108        native      = max_nonleaf    +   1
 109   };
 110 
 111   // The WaitSet and EntryList linked lists are composed of ParkEvents.
 112   // I use ParkEvent instead of threads as ParkEvents are immortal and
 113   // type-stable, meaning we can safely unpark() a possibly stale
 114   // list element in the unlock()-path.
 115 
 116  protected:                              // Monitor-Mutex metadata
 117   SplitWord _LockWord ;                  // Contention queue (cxq) colocated with Lock-byte
 118   enum LockWordBits { _LBIT=1 } ;
 119   Thread * volatile _owner;              // The owner of the lock
 120                                          // Consider sequestering _owner on its own $line
 121                                          // to aid future synchronization mechanisms.
 122   ParkEvent * volatile _EntryList ;      // List of threads waiting for entry
 123   ParkEvent * volatile _OnDeck ;         // heir-presumptive
 124   volatile intptr_t _WaitLock [1] ;      // Protects _WaitSet
 125   ParkEvent * volatile  _WaitSet ;       // LL of ParkEvents
 126   volatile bool     _snuck;              // Used for sneaky locking (evil).
 127   int NotifyCount ;                      // diagnostic assist

 128 
 129   // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
 130 #ifndef PRODUCT
 131   bool      _allow_vm_block;
 132   debug_only(int _rank;)                 // rank (to avoid/detect potential deadlocks)
 133   debug_only(Monitor * _next;)           // Used by a Thread to link up owned locks
 134   debug_only(Thread* _last_owner;)       // the last thread to own the lock



 135 #endif
 136 




 137  // platform-dependent support code can go here (in os_<os_family>.cpp)
 138  public:
 139   enum {
 140     _no_safepoint_check_flag    = true,
 141     _allow_vm_block_flag        = true,
 142     _as_suspend_equivalent_flag = true
 143   };
 144 
 145   // Locks can be acquired with or without safepoint check.
 146   // Monitor::lock and Monitor::lock_without_safepoint_check
 147   // checks these flags when acquiring a lock to ensure
 148   // consistent checking for each lock.
 149   // A few existing locks will sometimes have a safepoint check and
 150   // sometimes not, but these locks are set up in such a way to avoid deadlocks.
 151   enum SafepointCheckRequired {
 152     _safepoint_check_never,       // Monitors with this value will cause errors
 153                                   // when acquired with a safepoint check.
 154     _safepoint_check_sometimes,   // Certain locks are called sometimes with and
 155                                   // sometimes without safepoint checks. These
 156                                   // locks will not produce errors when locked.
 157     _safepoint_check_always       // Causes error if locked without a safepoint
 158                                   // check.
 159   };
 160 
 161   NOT_PRODUCT(SafepointCheckRequired _safepoint_check_required;)
 162 
 163   enum WaitResults {
 164     CONDVAR_EVENT,         // Wait returned because of condition variable notification
 165     INTERRUPT_EVENT,       // Wait returned because waiting thread was interrupted
 166     NUMBER_WAIT_RESULTS
 167   };
 168 };
 169 
 170 class Monitor : public MonitorBase {
 171  protected:
 172   // The default length of monitor name is chosen to avoid false sharing.
 173   enum {
 174     CACHE_LINE_PADDING = DEFAULT_CACHE_LINE_SIZE - sizeof(MonitorBase),
 175     MONITOR_NAME_LEN = CACHE_LINE_PADDING > 64 ? CACHE_LINE_PADDING : 64
 176   };
 177   char _name[MONITOR_NAME_LEN];          // Name of mutex
 178   // Other fields should be declared in MonitorBase.
 179 
 180  public:
 181 #ifndef PRODUCT
 182   debug_only(static bool contains(Monitor * locks, Monitor * lock);)
 183   debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);)
 184   debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);)
 185 #endif
 186 
 187   void set_owner_implementation(Thread* owner)                        PRODUCT_RETURN;
 188   void check_prelock_state     (Thread* thread)                       PRODUCT_RETURN;
 189   void check_block_state       (Thread* thread)                       PRODUCT_RETURN;
 190 
 191  private:
 192    int  TrySpin (Thread * Self) ;
 193    int  TryLock () ;
 194    int  TryFast () ;
 195    int  AcquireOrPush (ParkEvent * ev) ;
 196    void IUnlock (bool RelaxAssert) ;
 197    void ILock (Thread * Self) ;
 198    int  IWait (Thread * Self, jlong timo);
 199    int  ILocked () ;
 200 
 201  protected:
 202    static void ClearMonitor (Monitor * m, const char* name = NULL) ;
 203    Monitor() ;
 204 
 205  public:
 206   Monitor(int rank, const char *name, bool allow_vm_block = false,
 207           SafepointCheckRequired safepoint_check_required = _safepoint_check_always);
 208   ~Monitor();
 209 
 210   // Wait until monitor is notified (or times out).
 211   // Defaults are to make safepoint checks, wait time is forever (i.e.,
 212   // zero), and not a suspend-equivalent condition. Returns true if wait
 213   // times out; otherwise returns false.
 214   bool wait(bool no_safepoint_check = !_no_safepoint_check_flag,
 215             long timeout = 0,
 216             bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
 217   bool notify();
 218   bool notify_all();
 219 
 220 
 221   void lock(); // prints out warning if VM thread blocks
 222   void lock(Thread *thread); // overloaded with current thread
 223   void unlock();
 224   bool is_locked() const                     { return _owner != NULL; }
 225 
 226   bool try_lock(); // Like lock(), but unblocking. It returns false instead
 227 
 228   // Lock without safepoint check. Should ONLY be used by safepoint code and other code
 229   // that is guaranteed not to block while running inside the VM.
 230   void lock_without_safepoint_check();
 231   void lock_without_safepoint_check (Thread * Self) ;
 232 
 233   // Current owner - not not MT-safe. Can only be used to guarantee that
 234   // the current running thread owns the lock
 235   Thread* owner() const         { return _owner; }
 236   bool owned_by_self() const;
 237 
 238   // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by
 239   // non-Java thread. (We should really have a RawMonitor abstraction)
 240   void jvm_raw_lock();
 241   void jvm_raw_unlock();
 242   const char *name() const                  { return _name; }
 243 
 244   void print_on_error(outputStream* st) const;
 245 
 246   #ifndef PRODUCT
 247     void print_on(outputStream* st) const;
 248     void print() const                      { print_on(tty); }
 249     debug_only(int    rank() const          { return _rank; })
 250     bool   allow_vm_block()                 { return _allow_vm_block; }
 251 
 252     debug_only(Monitor *next()  const         { return _next; })
 253     debug_only(void   set_next(Monitor *next) { _next = next; })
 254   #endif
 255 
 256   void set_owner(Thread* owner) {
 257   #ifndef PRODUCT
 258     set_owner_implementation(owner);
 259     debug_only(void verify_Monitor(Thread* thr));
 260   #else
 261     _owner = owner;
 262   #endif
 263   }
 264 
 265 };
 266 
 267 // Normally we'd expect Monitor to extend Mutex in the sense that a monitor
 268 // constructed from pthreads primitives might extend a mutex by adding
 269 // a condvar and some extra metadata.  In fact this was the case until J2SE7.
 270 //
 271 // Currently, however, the base object is a monitor.  Monitor contains all the
 272 // logic for wait(), notify(), etc.   Mutex extends monitor and restricts the
 273 // visibility of wait(), notify(), and notify_all().
 274 //
 275 // Another viable alternative would have been to have Monitor extend Mutex and
 276 // implement all the normal mutex and wait()-notify() logic in Mutex base class.
 277 // The wait()-notify() facility would be exposed via special protected member functions
 278 // (e.g., _Wait() and _Notify()) in Mutex.  Monitor would extend Mutex and expose wait()
 279 // as a call to _Wait().  That is, the public wait() would be a wrapper for the protected
 280 // _Wait().
 281 //
 282 // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead.
 283 // After all, monitors are sufficient for Java-level synchronization.   At one point in time
 284 // there may have been some benefit to having distinct mutexes and monitors, but that time
 285 // has past.
 286 //
 287 // The Mutex/Monitor design parallels that of Java-monitors, being based on
 288 // thread-specific park-unpark platform-specific primitives.
 289 
 290 
 291 class Mutex : public Monitor {      // degenerate Monitor
 292  public:
 293    Mutex(int rank, const char *name, bool allow_vm_block = false,
 294          SafepointCheckRequired safepoint_check_required = _safepoint_check_always);
 295    ~Mutex () ;
 296  private:
 297    bool notify ()    { ShouldNotReachHere(); return false; }
 298    bool notify_all() { ShouldNotReachHere(); return false; }
 299    bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
 300      ShouldNotReachHere() ;
 301      return false ;
 302    }
 303 };
 304 
 305 
 306 #endif // SHARE_VM_RUNTIME_MUTEX_HPP
--- EOF ---