Thu, 20 Nov 2008 16:56:09 -0800
6684579: SoftReference processing can be made more efficient
Summary: For current soft-ref clearing policies, we can decide at marking time if a soft-reference will definitely not be cleared, postponing the decision of whether it will definitely be cleared to the final reference processing phase. This can be especially beneficial in the case of concurrent collectors where the marking is usually concurrent but reference processing is usually not.
Reviewed-by: jmasa
1 /*
2 * Copyright 2005 Sun Microsystems, Inc. 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.
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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).
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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.
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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23 */
26 // Forward declarations
27 class YieldingFlexibleWorkGang;
29 // Status of tasks
30 enum Status {
31 INACTIVE,
32 ACTIVE,
33 YIELDING,
34 YIELDED,
35 ABORTING,
36 ABORTED,
37 COMPLETING,
38 COMPLETED
39 };
41 // Class YieldingFlexibleGangWorker:
42 // Several instances of this class run in parallel as workers for a gang.
43 class YieldingFlexibleGangWorker: public GangWorker {
44 public:
45 // Ctor
46 YieldingFlexibleGangWorker(AbstractWorkGang* gang, int id) :
47 GangWorker(gang, id) { }
49 public:
50 YieldingFlexibleWorkGang* yf_gang() const
51 { return (YieldingFlexibleWorkGang*)gang(); }
53 protected: // Override from parent class
54 virtual void loop();
55 };
57 // An abstract task to be worked on by a flexible work gang,
58 // and where the workers will periodically yield, usually
59 // in response to some condition that is signalled by means
60 // that are specific to the task at hand.
61 // You subclass this to supply your own work() method.
62 // A second feature of this kind of work gang is that
63 // it allows for the signalling of certain exceptional
64 // conditions that may be encountered during the performance
65 // of the task and that may require the task at hand to be
66 // `aborted' forthwith. Finally, these gangs are `flexible'
67 // in that they can operate at partial capacity with some
68 // gang workers waiting on the bench; in other words, the
69 // size of the active worker pool can flex (up to an apriori
70 // maximum) in response to task requests at certain points.
71 // The last part (the flexible part) has not yet been fully
72 // fleshed out and is a work in progress.
73 class YieldingFlexibleGangTask: public AbstractGangTask {
74 Status _status;
75 YieldingFlexibleWorkGang* _gang;
76 int _actual_size; // size of gang obtained
78 protected:
79 int _requested_size; // size of gang requested
81 // Constructor and desctructor: only construct subclasses.
82 YieldingFlexibleGangTask(const char* name): AbstractGangTask(name),
83 _status(INACTIVE),
84 _gang(NULL),
85 _requested_size(0) { }
87 virtual ~YieldingFlexibleGangTask() { }
89 friend class YieldingFlexibleWorkGang;
90 friend class YieldingFlexibleGangWorker;
91 NOT_PRODUCT(virtual bool is_YieldingFlexibleGang_task() const {
92 return true;
93 })
95 void set_status(Status s) {
96 _status = s;
97 }
98 YieldingFlexibleWorkGang* gang() {
99 return _gang;
100 }
101 void set_gang(YieldingFlexibleWorkGang* gang) {
102 assert(_gang == NULL || gang == NULL, "Clobber without intermediate reset?");
103 _gang = gang;
104 }
106 public:
107 // The abstract work method.
108 // The argument tells you which member of the gang you are.
109 virtual void work(int i) = 0;
111 // Subclasses should call the parent's yield() method
112 // after having done any work specific to the subclass.
113 virtual void yield();
115 // An abstract method supplied by
116 // a concrete sub-class which is used by the coordinator
117 // to do any "central yielding" work.
118 virtual void coordinator_yield() = 0;
120 // Subclasses should call the parent's abort() method
121 // after having done any work specific to the sunbclass.
122 virtual void abort();
124 Status status() const { return _status; }
125 bool yielded() const { return _status == YIELDED; }
126 bool completed() const { return _status == COMPLETED; }
127 bool aborted() const { return _status == ABORTED; }
128 bool active() const { return _status == ACTIVE; }
130 int requested_size() const { return _requested_size; }
131 int actual_size() const { return _actual_size; }
133 void set_requested_size(int sz) { _requested_size = sz; }
134 void set_actual_size(int sz) { _actual_size = sz; }
135 };
137 // Class YieldingWorkGang: A subclass of WorkGang.
138 // In particular, a YieldingWorkGang is made up of
139 // YieldingGangWorkers, and provides infrastructure
140 // supporting yielding to the "GangOverseer",
141 // being the thread that orchestrates the WorkGang via run_task().
142 class YieldingFlexibleWorkGang: public AbstractWorkGang {
143 // Here's the public interface to this class.
144 public:
145 // Constructor and destructor.
146 YieldingFlexibleWorkGang(const char* name, int workers,
147 bool are_GC_task_threads);
149 YieldingFlexibleGangTask* yielding_task() const {
150 assert(task() == NULL || task()->is_YieldingFlexibleGang_task(),
151 "Incorrect cast");
152 return (YieldingFlexibleGangTask*)task();
153 }
154 // Run a task; returns when the task is done, or the workers yield,
155 // or the task is aborted, or the work gang is terminated via stop().
156 // A task that has been yielded can be continued via this same interface
157 // by using the same task repeatedly as the argument to the call.
158 // It is expected that the YieldingFlexibleGangTask carries the appropriate
159 // continuation information used by workers to continue the task
160 // from its last yield point. Thus, a completed task will return
161 // immediately with no actual work having been done by the workers.
162 void run_task(AbstractGangTask* task) {
163 guarantee(false, "Use start_task instead");
164 }
165 void start_task(YieldingFlexibleGangTask* new_task);
166 void continue_task(YieldingFlexibleGangTask* gang_task);
168 // Abort a currently running task, if any; returns when all the workers
169 // have stopped working on the current task and have returned to their
170 // waiting stations.
171 void abort_task();
173 // Yield: workers wait at their current working stations
174 // until signalled to proceed by the overseer.
175 void yield();
177 // Abort: workers are expected to return to their waiting
178 // stations, whence they are ready for the next task dispatched
179 // by the overseer.
180 void abort();
182 private:
183 // The currently active workers in this gang.
184 // This is a number that is dynamically adjusted by
185 // the run_task() method at each subsequent invocation,
186 // using data in the YieldingFlexibleGangTask.
187 int _active_workers;
188 int _yielded_workers;
189 void wait_for_gang();
191 public:
192 // Accessors for fields
193 int active_workers() const {
194 return _active_workers;
195 }
197 int yielded_workers() const {
198 return _yielded_workers;
199 }
201 private:
202 friend class YieldingFlexibleGangWorker;
203 void reset(); // NYI
204 };