diff -r 000000000000 -r f90c822e73f8 src/share/vm/runtime/park.hpp --- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/share/vm/runtime/park.hpp Wed Apr 27 01:25:04 2016 +0800 @@ -0,0 +1,177 @@ +/* + * Copyright (c) 1997, 2013, 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. + * + */ + +#ifndef SHARE_VM_RUNTIME_PARK_HPP +#define SHARE_VM_RUNTIME_PARK_HPP + +#include "utilities/debug.hpp" +#include "utilities/globalDefinitions.hpp" +/* + * 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) throw(); + void operator delete (void * a) ; + + public: + static ParkEvent * Allocate (Thread * t) ; + static void Release (ParkEvent * e) ; +} ; + +#endif // SHARE_VM_RUNTIME_PARK_HPP