jdk8-mips64-public/hotspot: src/share/vm/runtime/mutex.hpp@d1605aabd0a1 (annotated)

src/share/vm/runtime/mutex.hpp@d1605aabd0a1 (annotated)

src/share/vm/runtime/mutex.hpp

Wed, 02 Jul 2008 12:55:16 -0700

author: xdono
date: Wed, 02 Jul 2008 12:55:16 -0700
changeset 631: d1605aabd0a1
parent 490: 2a8eb116ebbe
child 1040: 98cb887364d3
permissions: -rw-r--r--

6719955: Update copyright year
Summary: Update copyright year for files that have been modified in 2008
Reviewed-by: ohair, tbell

 /*
  * Copyright 1998-2008 Sun Microsystems, Inc.  All Rights Reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License version 2 only, as
  * published by the Free Software Foundation.
  *
  * This code is distributed in the hope that it will be useful, but WITHOUT
  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  * version 2 for more details (a copy is included in the LICENSE file that
  * accompanied this code).
  *
  * You should have received a copy of the GNU General Public License version
  * 2 along with this work; if not, write to the Free Software Foundation,
  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  *
  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
  * CA 95054 USA or visit www.sun.com if you need additional information or
  * have any questions.
  *
  */
 // The SplitWord construct allows us to colocate the contention queue
 // (cxq) with the lock-byte.  The queue elements are ParkEvents, which are
 // always aligned on 256-byte addresses - the least significant byte of
 // a ParkEvent is always 0.  Colocating the lock-byte with the queue
 // allows us to easily avoid what would otherwise be a race in lock()
 // if we were to use two completely separate fields for the contention queue
 // and the lock indicator.  Specifically, colocation renders us immune
 // from the race where a thread might enqueue itself in the lock() slow-path
 // immediately after the lock holder drops the outer lock in the unlock()
 // fast-path.
 //
 // Colocation allows us to use a fast-path unlock() form that uses
 // A MEMBAR instead of a CAS.  MEMBAR has lower local latency than CAS
 // on many platforms.
 //
 // See:
 // +  http://blogs.sun.com/dave/entry/biased_locking_in_hotspot
 // +  http://blogs.sun.com/dave/resource/synchronization-public2.pdf
 //
 // Note that we're *not* using word-tearing the classic sense.
 // The lock() fast-path will CAS the lockword and the unlock()
 // fast-path will store into the lock-byte colocated within the lockword.
 // We depend on the fact that all our reference platforms have
 // coherent and atomic byte accesses.  More precisely, byte stores
 // interoperate in a safe, sane, and expected manner with respect to
 // CAS, ST and LDs to the full-word containing the byte.
 // If you're porting HotSpot to a platform where that isn't the case
 // then you'll want change the unlock() fast path from:
 //    STB;MEMBAR #storeload; LDN
 // to a full-word CAS of the lockword.
 union SplitWord {   // full-word with separately addressable LSB
   volatile intptr_t FullWord ;
   volatile void * Address ;
   volatile jbyte Bytes [sizeof(intptr_t)] ;
 } ;
 // Endian-ness ... index of least-significant byte in SplitWord.Bytes[]
 #ifdef AMD64        // little
  #define _LSBINDEX 0
 #else
 #if IA32            // little
  #define _LSBINDEX 0
 #else
 #ifdef SPARC        // big
  #define _LSBINDEX (sizeof(intptr_t)-1)
 #else
  #error "unknown architecture"
 #endif
 #endif
 #endif
 class ParkEvent ;
 // See orderAccess.hpp.  We assume throughout the VM that mutex lock and
 // try_lock do fence-lock-acquire, and that unlock does a release-unlock,
 // *in that order*.  If their implementations change such that these
 // assumptions are violated, a whole lot of code will break.
 // The default length of monitor name is choosen to be 64 to avoid false sharing.
 static const int MONITOR_NAME_LEN = 64;
 class Monitor : public CHeapObj {
  public:
   // A special lock: Is a lock where you are guaranteed not to block while you are
   // holding it, i.e., no vm operation can happen, taking other locks, etc.
   // NOTE: It is critical that the rank 'special' be the lowest (earliest)
   // (except for "event"?) for the deadlock dection to work correctly.
   // The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
   // which being external to the VM are not subject to deadlock detection.
   // The rank safepoint is used only for synchronization in reaching a
   // safepoint and leaving a safepoint.  It is only used for the Safepoint_lock
   // currently.  While at a safepoint no mutexes of rank safepoint are held
   // by any thread.
   // The rank named "leaf" is probably historical (and should
   // be changed) -- mutexes of this rank aren't really leaf mutexes
   // at all.
   enum lock_types {
        event,
        special,
        suspend_resume,
        leaf        = suspend_resume +   2,
        safepoint   = leaf           +  10,
        barrier     = safepoint      +   1,
        nonleaf     = barrier        +   1,
        max_nonleaf = nonleaf        + 900,
        native      = max_nonleaf    +   1
   };
   // The WaitSet and EntryList linked lists are composed of ParkEvents.
   // I use ParkEvent instead of threads as ParkEvents are immortal and
   // type-stable, meaning we can safely unpark() a possibly stale
   // list element in the unlock()-path.
  protected:                              // Monitor-Mutex metadata
   SplitWord _LockWord ;                  // Contention queue (cxq) colocated with Lock-byte
   enum LockWordBits { _LBIT=1 } ;
   Thread * volatile _owner;              // The owner of the lock
                                          // Consider sequestering _owner on its own $line
                                          // to aid future synchronization mechanisms.
   ParkEvent * volatile _EntryList ;      // List of threads waiting for entry
   ParkEvent * volatile _OnDeck ;         // heir-presumptive
   volatile intptr_t _WaitLock [1] ;      // Protects _WaitSet
   ParkEvent * volatile  _WaitSet ;       // LL of ParkEvents
   volatile bool     _snuck;              // Used for sneaky locking (evil).
   int NotifyCount ;                      // diagnostic assist
   char _name[MONITOR_NAME_LEN];          // Name of mutex
   // Debugging fields for naming, deadlock detection, etc. (some only used in debug mode)
 #ifndef PRODUCT
   bool      _allow_vm_block;
   debug_only(int _rank;)                 // rank (to avoid/detect potential deadlocks)
   debug_only(Monitor * _next;)           // Used by a Thread to link up owned locks
   debug_only(Thread* _last_owner;)       // the last thread to own the lock
   debug_only(static bool contains(Monitor * locks, Monitor * lock);)
   debug_only(static Monitor * get_least_ranked_lock(Monitor * locks);)
   debug_only(Monitor * get_least_ranked_lock_besides_this(Monitor * locks);)
 #endif
   void set_owner_implementation(Thread* owner)                        PRODUCT_RETURN;
   void check_prelock_state     (Thread* thread)                       PRODUCT_RETURN;
   void check_block_state       (Thread* thread)                       PRODUCT_RETURN;
   // platform-dependent support code can go here (in os_<os_family>.cpp)
  public:
   enum {
     _no_safepoint_check_flag    = true,
     _allow_vm_block_flag        = true,
     _as_suspend_equivalent_flag = true
   };
   enum WaitResults {
     CONDVAR_EVENT,         // Wait returned because of condition variable notification
     INTERRUPT_EVENT,       // Wait returned because waiting thread was interrupted
     NUMBER_WAIT_RESULTS
   };
  private:
    int  TrySpin (Thread * Self) ;
    int  TryLock () ;
    int  TryFast () ;
    int  AcquireOrPush (ParkEvent * ev) ;
    void IUnlock (bool RelaxAssert) ;
    void ILock (Thread * Self) ;
    int  IWait (Thread * Self, jlong timo);
    int  ILocked () ;
  protected:
    static void ClearMonitor (Monitor * m, const char* name = NULL) ;
    Monitor() ;
  public:
   Monitor(int rank, const char *name, bool allow_vm_block=false);
   ~Monitor();
   // Wait until monitor is notified (or times out).
   // Defaults are to make safepoint checks, wait time is forever (i.e.,
   // zero), and not a suspend-equivalent condition. Returns true if wait
   // times out; otherwise returns false.
   bool wait(bool no_safepoint_check = !_no_safepoint_check_flag,
             long timeout = 0,
             bool as_suspend_equivalent = !_as_suspend_equivalent_flag);
   bool notify();
   bool notify_all();
   void lock(); // prints out warning if VM thread blocks
   void lock(Thread *thread); // overloaded with current thread
   void unlock();
   bool is_locked() const                     { return _owner != NULL; }
   bool try_lock(); // Like lock(), but unblocking. It returns false instead
   // Lock without safepoint check. Should ONLY be used by safepoint code and other code
   // that is guaranteed not to block while running inside the VM.
   void lock_without_safepoint_check();
   void lock_without_safepoint_check (Thread * Self) ;
   // Current owner - not not MT-safe. Can only be used to guarantee that
   // the current running thread owns the lock
   Thread* owner() const         { return _owner; }
   bool owned_by_self() const;
   // Support for JVM_RawMonitorEnter & JVM_RawMonitorExit. These can be called by
   // non-Java thread. (We should really have a RawMonitor abstraction)
   void jvm_raw_lock();
   void jvm_raw_unlock();
   const char *name() const                  { return _name; }
   void print_on_error(outputStream* st) const;
   #ifndef PRODUCT
     void print_on(outputStream* st) const;
     void print() const                      { print_on(tty); }
     debug_only(int    rank() const          { return _rank; })
     bool   allow_vm_block()                 { return _allow_vm_block; }
     debug_only(Monitor *next()  const         { return _next; })
     debug_only(void   set_next(Monitor *next) { _next = next; })
   #endif
   void set_owner(Thread* owner) {
   #ifndef PRODUCT
     set_owner_implementation(owner);
     debug_only(void verify_Monitor(Thread* thr));
   #else
     _owner = owner;
   #endif
   }
 };
 // Normally we'd expect Monitor to extend Mutex in the sense that a monitor
 // constructed from pthreads primitives might extend a mutex by adding
 // a condvar and some extra metadata.  In fact this was the case until J2SE7.
 //
 // Currently, however, the base object is a monitor.  Monitor contains all the
 // logic for wait(), notify(), etc.   Mutex extends monitor and restricts the
 // visiblity of wait(), notify(), and notify_all().
 //
 // Another viable alternative would have been to have Monitor extend Mutex and
 // implement all the normal mutex and wait()-notify() logic in Mutex base class.
 // The wait()-notify() facility would be exposed via special protected member functions
 // (e.g., _Wait() and _Notify()) in Mutex.  Monitor would extend Mutex and expose wait()
 // as a call to _Wait().  That is, the public wait() would be a wrapper for the protected
 // _Wait().
 //
 // An even better alternative is to simply eliminate Mutex:: and use Monitor:: instead.
 // After all, monitors are sufficient for Java-level synchronization.   At one point in time
 // there may have been some benefit to having distinct mutexes and monitors, but that time
 // has past.
 //
 // The Mutex/Monitor design parallels that of Java-monitors, being based on
 // thread-specific park-unpark platform-specific primitives.
 class Mutex : public Monitor {      // degenerate Monitor
  public:
    Mutex (int rank, const char *name, bool allow_vm_block=false);
    ~Mutex () ;
  private:
    bool notify ()    { ShouldNotReachHere(); return false; }
    bool notify_all() { ShouldNotReachHere(); return false; }
    bool wait (bool no_safepoint_check, long timeout, bool as_suspend_equivalent) {
      ShouldNotReachHere() ;
      return false ;
    }
 };
 /*
  * Per-thread blocking support for JSR166. See the Java-level
  * Documentation for rationale. Basically, park acts like wait, unpark
  * like notify.
  *
  * 6271289 --
  * To avoid errors where an os thread expires but the JavaThread still
  * exists, Parkers are immortal (type-stable) and are recycled across
  * new threads.  This parallels the ParkEvent implementation.
  * Because park-unpark allow spurious wakeups it is harmless if an
  * unpark call unparks a new thread using the old Parker reference.
  *
  * In the future we'll want to think about eliminating Parker and using
  * ParkEvent instead.  There's considerable duplication between the two
  * services.
  *
  */
 class Parker : public os::PlatformParker {
 private:
   volatile int _counter ;
   Parker * FreeNext ;
   JavaThread * AssociatedWith ; // Current association
 public:
   Parker() : PlatformParker() {
     _counter       = 0 ;
     FreeNext       = NULL ;
     AssociatedWith = NULL ;
   }
 protected:
   ~Parker() { ShouldNotReachHere(); }
 public:
   // For simplicity of interface with Java, all forms of park (indefinite,
   // relative, and absolute) are multiplexed into one call.
   void park(bool isAbsolute, jlong time);
   void unpark();
   // Lifecycle operators
   static Parker * Allocate (JavaThread * t) ;
   static void Release (Parker * e) ;
 private:
   static Parker * volatile FreeList ;
   static volatile int ListLock ;
 };

Mercurial > jdk8-mips64-public > hotspot / annotate

src/share/vm/runtime/mutex.hpp@d1605aabd0a1 (annotated)

src/share/vm/runtime/mutex.hpp