| /* |
| * Copyright (c) 1997, 2015, 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 ; |
| |
| public: |
| // MCS-CLH list linkage and Native Mutex/Monitor |
| ParkEvent * volatile ListNext ; |
| volatile intptr_t OnList ; |
| volatile int TState ; |
| volatile int Notified ; // for native monitor construct |
| |
| 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 ; |
| OnList = 0 ; |
| TState = 0 ; |
| Notified = 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 |