Mercurial > hg > truffle
view src/share/vm/runtime/park.hpp @ 3273:df22fe9c5a93
Merge
author | coleenp |
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date | Wed, 27 Apr 2011 17:25:45 -0700 |
parents | f95d63e2154a |
children | 9758d9f36299 |
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/* * 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. * */ #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) ; void operator delete (void * a) ; public: static ParkEvent * Allocate (Thread * t) ; static void Release (ParkEvent * e) ; } ; #endif // SHARE_VM_RUNTIME_PARK_HPP