|
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 } ; |