Mercurial > hg > graal-jvmci-8
comparison src/share/vm/runtime/park.hpp @ 1878:fa83ab460c54
6988353: refactor contended sync subsystem
Summary: reduce complexity by factoring synchronizer.cpp
Reviewed-by: dholmes, never, coleenp
author | acorn |
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date | Fri, 22 Oct 2010 15:59:34 -0400 |
parents | |
children | f95d63e2154a |
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1874:75ab0162aa84 | 1878:fa83ab460c54 |
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1 /* | |
2 * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved. | |
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
4 * | |
5 * This code is free software; you can redistribute it and/or modify it | |
6 * under the terms of the GNU General Public License version 2 only, as | |
7 * published by the Free Software Foundation. | |
8 * | |
9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
12 * version 2 for more details (a copy is included in the LICENSE file that | |
13 * accompanied this code). | |
14 * | |
15 * You should have received a copy of the GNU General Public License version | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
18 * | |
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | |
20 * or visit www.oracle.com if you need additional information or have any | |
21 * questions. | |
22 * | |
23 */ | |
24 /* | |
25 * Per-thread blocking support for JSR166. See the Java-level | |
26 * Documentation for rationale. Basically, park acts like wait, unpark | |
27 * like notify. | |
28 * | |
29 * 6271289 -- | |
30 * To avoid errors where an os thread expires but the JavaThread still | |
31 * exists, Parkers are immortal (type-stable) and are recycled across | |
32 * new threads. This parallels the ParkEvent implementation. | |
33 * Because park-unpark allow spurious wakeups it is harmless if an | |
34 * unpark call unparks a new thread using the old Parker reference. | |
35 * | |
36 * In the future we'll want to think about eliminating Parker and using | |
37 * ParkEvent instead. There's considerable duplication between the two | |
38 * services. | |
39 * | |
40 */ | |
41 | |
42 class Parker : public os::PlatformParker { | |
43 private: | |
44 volatile int _counter ; | |
45 Parker * FreeNext ; | |
46 JavaThread * AssociatedWith ; // Current association | |
47 | |
48 public: | |
49 Parker() : PlatformParker() { | |
50 _counter = 0 ; | |
51 FreeNext = NULL ; | |
52 AssociatedWith = NULL ; | |
53 } | |
54 protected: | |
55 ~Parker() { ShouldNotReachHere(); } | |
56 public: | |
57 // For simplicity of interface with Java, all forms of park (indefinite, | |
58 // relative, and absolute) are multiplexed into one call. | |
59 void park(bool isAbsolute, jlong time); | |
60 void unpark(); | |
61 | |
62 // Lifecycle operators | |
63 static Parker * Allocate (JavaThread * t) ; | |
64 static void Release (Parker * e) ; | |
65 private: | |
66 static Parker * volatile FreeList ; | |
67 static volatile int ListLock ; | |
68 | |
69 }; | |
70 | |
71 ///////////////////////////////////////////////////////////// | |
72 // | |
73 // ParkEvents are type-stable and immortal. | |
74 // | |
75 // Lifecycle: Once a ParkEvent is associated with a thread that ParkEvent remains | |
76 // associated with the thread for the thread's entire lifetime - the relationship is | |
77 // stable. A thread will be associated at most one ParkEvent. When the thread | |
78 // expires, the ParkEvent moves to the EventFreeList. New threads attempt to allocate from | |
79 // the EventFreeList before creating a new Event. Type-stability frees us from | |
80 // worrying about stale Event or Thread references in the objectMonitor subsystem. | |
81 // (A reference to ParkEvent is always valid, even though the event may no longer be associated | |
82 // with the desired or expected thread. A key aspect of this design is that the callers of | |
83 // park, unpark, etc must tolerate stale references and spurious wakeups). | |
84 // | |
85 // Only the "associated" thread can block (park) on the ParkEvent, although | |
86 // any other thread can unpark a reachable parkevent. Park() is allowed to | |
87 // return spuriously. In fact park-unpark a really just an optimization to | |
88 // avoid unbounded spinning and surrender the CPU to be a polite system citizen. | |
89 // A degenerate albeit "impolite" park-unpark implementation could simply return. | |
90 // See http://blogs.sun.com/dave for more details. | |
91 // | |
92 // Eventually I'd like to eliminate Events and ObjectWaiters, both of which serve as | |
93 // thread proxies, and simply make the THREAD structure type-stable and persistent. | |
94 // Currently, we unpark events associated with threads, but ideally we'd just | |
95 // unpark threads. | |
96 // | |
97 // The base-class, PlatformEvent, is platform-specific while the ParkEvent is | |
98 // platform-independent. PlatformEvent provides park(), unpark(), etc., and | |
99 // is abstract -- that is, a PlatformEvent should never be instantiated except | |
100 // as part of a ParkEvent. | |
101 // Equivalently we could have defined a platform-independent base-class that | |
102 // exported Allocate(), Release(), etc. The platform-specific class would extend | |
103 // that base-class, adding park(), unpark(), etc. | |
104 // | |
105 // A word of caution: The JVM uses 2 very similar constructs: | |
106 // 1. ParkEvent are used for Java-level "monitor" synchronization. | |
107 // 2. Parkers are used by JSR166-JUC park-unpark. | |
108 // | |
109 // We'll want to eventually merge these redundant facilities and use ParkEvent. | |
110 | |
111 | |
112 class ParkEvent : public os::PlatformEvent { | |
113 private: | |
114 ParkEvent * FreeNext ; | |
115 | |
116 // Current association | |
117 Thread * AssociatedWith ; | |
118 intptr_t RawThreadIdentity ; // LWPID etc | |
119 volatile int Incarnation ; | |
120 | |
121 // diagnostic : keep track of last thread to wake this thread. | |
122 // this is useful for construction of dependency graphs. | |
123 void * LastWaker ; | |
124 | |
125 public: | |
126 // MCS-CLH list linkage and Native Mutex/Monitor | |
127 ParkEvent * volatile ListNext ; | |
128 ParkEvent * volatile ListPrev ; | |
129 volatile intptr_t OnList ; | |
130 volatile int TState ; | |
131 volatile int Notified ; // for native monitor construct | |
132 volatile int IsWaiting ; // Enqueued on WaitSet | |
133 | |
134 | |
135 private: | |
136 static ParkEvent * volatile FreeList ; | |
137 static volatile int ListLock ; | |
138 | |
139 // It's prudent to mark the dtor as "private" | |
140 // ensuring that it's not visible outside the package. | |
141 // Unfortunately gcc warns about such usage, so | |
142 // we revert to the less desirable "protected" visibility. | |
143 // The other compilers accept private dtors. | |
144 | |
145 protected: // Ensure dtor is never invoked | |
146 ~ParkEvent() { guarantee (0, "invariant") ; } | |
147 | |
148 ParkEvent() : PlatformEvent() { | |
149 AssociatedWith = NULL ; | |
150 FreeNext = NULL ; | |
151 ListNext = NULL ; | |
152 ListPrev = NULL ; | |
153 OnList = 0 ; | |
154 TState = 0 ; | |
155 Notified = 0 ; | |
156 IsWaiting = 0 ; | |
157 } | |
158 | |
159 // We use placement-new to force ParkEvent instances to be | |
160 // aligned on 256-byte address boundaries. This ensures that the least | |
161 // significant byte of a ParkEvent address is always 0. | |
162 | |
163 void * operator new (size_t sz) ; | |
164 void operator delete (void * a) ; | |
165 | |
166 public: | |
167 static ParkEvent * Allocate (Thread * t) ; | |
168 static void Release (ParkEvent * e) ; | |
169 } ; |