jdk8-mips64-public/hotspot: src/share/vm/runtime/park.hpp@fa83ab460c54 (annotated)

src/share/vm/runtime/park.hpp@fa83ab460c54 (annotated)

src/share/vm/runtime/park.hpp

Fri, 22 Oct 2010 15:59:34 -0400

author: acorn
date: Fri, 22 Oct 2010 15:59:34 -0400
changeset 2233: fa83ab460c54
child 2314: f95d63e2154a
permissions: -rw-r--r--

6988353: refactor contended sync subsystem
Summary: reduce complexity by factoring synchronizer.cpp
Reviewed-by: dholmes, never, coleenp

 /*
  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */
 /*
  * 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 ;
 };
 /////////////////////////////////////////////////////////////
 //
 // ParkEvents are type-stable and immortal.
 //
 // Lifecycle: Once a ParkEvent is associated with a thread that ParkEvent remains
 // associated with the thread for the thread's entire lifetime - the relationship is
 // stable. A thread will be associated at most one ParkEvent.  When the thread
 // expires, the ParkEvent moves to the EventFreeList.  New threads attempt to allocate from
 // the EventFreeList before creating a new Event.  Type-stability frees us from
 // worrying about stale Event or Thread references in the objectMonitor subsystem.
 // (A reference to ParkEvent is always valid, even though the event may no longer be associated
 // with the desired or expected thread.  A key aspect of this design is that the callers of
 // park, unpark, etc must tolerate stale references and spurious wakeups).
 //
 // Only the "associated" thread can block (park) on the ParkEvent, although
 // any other thread can unpark a reachable parkevent.  Park() is allowed to
 // return spuriously.  In fact park-unpark a really just an optimization to
 // avoid unbounded spinning and surrender the CPU to be a polite system citizen.
 // A degenerate albeit "impolite" park-unpark implementation could simply return.
 // See http://blogs.sun.com/dave for more details.
 //
 // Eventually I'd like to eliminate Events and ObjectWaiters, both of which serve as
 // thread proxies, and simply make the THREAD structure type-stable and persistent.
 // Currently, we unpark events associated with threads, but ideally we'd just
 // unpark threads.
 //
 // The base-class, PlatformEvent, is platform-specific while the ParkEvent is
 // platform-independent.  PlatformEvent provides park(), unpark(), etc., and
 // is abstract -- that is, a PlatformEvent should never be instantiated except
 // as part of a ParkEvent.
 // Equivalently we could have defined a platform-independent base-class that
 // exported Allocate(), Release(), etc.  The platform-specific class would extend
 // that base-class, adding park(), unpark(), etc.
 //
 // A word of caution: The JVM uses 2 very similar constructs:
 // 1. ParkEvent are used for Java-level "monitor" synchronization.
 // 2. Parkers are used by JSR166-JUC park-unpark.
 //
 // We'll want to eventually merge these redundant facilities and use ParkEvent.
 class ParkEvent : public os::PlatformEvent {
   private:
     ParkEvent * FreeNext ;
     // Current association
     Thread * AssociatedWith ;
     intptr_t RawThreadIdentity ;        // LWPID etc
     volatile int Incarnation ;
     // diagnostic : keep track of last thread to wake this thread.
     // this is useful for construction of dependency graphs.
     void * LastWaker ;
   public:
     // MCS-CLH list linkage and Native Mutex/Monitor
     ParkEvent * volatile ListNext ;
     ParkEvent * volatile ListPrev ;
     volatile intptr_t OnList ;
     volatile int TState ;
     volatile int Notified ;             // for native monitor construct
     volatile int IsWaiting ;            // Enqueued on WaitSet
   private:
     static ParkEvent * volatile FreeList ;
     static volatile int ListLock ;
     // It's prudent to mark the dtor as "private"
     // ensuring that it's not visible outside the package.
     // Unfortunately gcc warns about such usage, so
     // we revert to the less desirable "protected" visibility.
     // The other compilers accept private dtors.
   protected:        // Ensure dtor is never invoked
     ~ParkEvent() { guarantee (0, "invariant") ; }
     ParkEvent() : PlatformEvent() {
        AssociatedWith = NULL ;
        FreeNext       = NULL ;
        ListNext       = NULL ;
        ListPrev       = NULL ;
        OnList         = 0 ;
        TState         = 0 ;
        Notified       = 0 ;
        IsWaiting      = 0 ;
     }
     // We use placement-new to force ParkEvent instances to be
     // aligned on 256-byte address boundaries.  This ensures that the least
     // significant byte of a ParkEvent address is always 0.
     void * operator new (size_t sz) ;
     void operator delete (void * a) ;
   public:
     static ParkEvent * Allocate (Thread * t) ;
     static void Release (ParkEvent * e) ;
 } ;

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src/share/vm/runtime/park.hpp@fa83ab460c54 (annotated)

src/share/vm/runtime/park.hpp