1 /*
2 * Copyright (c) 2005, 2013, 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 #include "precompiled.hpp"
26 #include "utilities/macros.hpp"
27 #include "utilities/yieldingWorkgroup.hpp"
28
29 // Forward declaration of classes declared here.
30
31 class GangWorker;
32 class WorkData;
33
34 YieldingFlexibleWorkGang::YieldingFlexibleWorkGang(
35 const char* name, uint workers, bool are_GC_task_threads) :
36 FlexibleWorkGang(name, workers, are_GC_task_threads, false),
37 _yielded_workers(0) {}
38
39 GangWorker* YieldingFlexibleWorkGang::allocate_worker(uint which) {
40 YieldingFlexibleGangWorker* new_member =
41 new YieldingFlexibleGangWorker(this, which);
42 return (YieldingFlexibleGangWorker*) new_member;
43 }
44
45 // Run a task; returns when the task is done, or the workers yield,
46 // or the task is aborted, or the work gang is terminated via stop().
47 // A task that has been yielded can be continued via this interface
48 // by using the same task repeatedly as the argument to the call.
49 // It is expected that the YieldingFlexibleGangTask carries the appropriate
50 // continuation information used by workers to continue the task
51 // from its last yield point. Thus, a completed task will return
52 // immediately with no actual work having been done by the workers.
53 /////////////////////
54 // Implementatiuon notes: remove before checking XXX
55 /*
56 Each gang is working on a task at a certain time.
57 Some subset of workers may have yielded and some may
58 have finished their quota of work. Until this task has
59 been completed, the workers are bound to that task.
60 Once the task has been completed, the gang unbounds
61 itself from the task.
62
63 The yielding work gang thus exports two invokation
64 interfaces: run_task() and continue_task(). The
65 first is used to initiate a new task and bind it
66 to the workers; the second is used to continue an
67 already bound task that has yielded. Upon completion
68 the binding is released and a new binding may be
69 created.
70
71 The shape of a yielding work gang is as follows:
72
73 Overseer invokes run_task(*task).
74 Lock gang monitor
75 Check that there is no existing binding for the gang
76 If so, abort with an error
77 Else, create a new binding of this gang to the given task
78 Set number of active workers (as asked)
79 Notify workers that work is ready to be done
80 [the requisite # workers would then start up
81 and do the task]
82 Wait on the monitor until either
83 all work is completed or the task has yielded
84 -- this is normally done through
85 yielded + completed == active
86 [completed workers are rest to idle state by overseer?]
87 return appropriate status to caller
88
89 Overseer invokes continue_task(*task),
90 Lock gang monitor
91 Check that task is the same as current binding
92 If not, abort with an error
93 Else, set the number of active workers as requested?
94 Notify workers that they can continue from yield points
95 New workers can also start up as required
96 while satisfying the constraint that
97 active + yielded does not exceed required number
98 Wait (as above).
99
100 NOTE: In the above, for simplicity in a first iteration
101 our gangs will be of fixed population and will not
102 therefore be flexible work gangs, just yielding work
103 gangs. Once this works well, we will in a second
104 iteration.refinement introduce flexibility into
105 the work gang.
106
107 NOTE: we can always create a new gang per each iteration
108 in order to get the flexibility, but we will for now
109 desist that simplified route.
110
111 */
112 /////////////////////
113 void YieldingFlexibleWorkGang::start_task(YieldingFlexibleGangTask* new_task) {
114 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
115 assert(task() == NULL, "Gang currently tied to a task");
116 assert(new_task != NULL, "Null task");
117 // Bind task to gang
118 _task = new_task;
119 new_task->set_gang(this); // Establish 2-way binding to support yielding
120 _sequence_number++;
121
122 uint requested_size = new_task->requested_size();
123 assert(requested_size >= 0, "Should be non-negative");
124 if (requested_size != 0) {
125 _active_workers = MIN2(requested_size, total_workers());
126 } else {
127 _active_workers = active_workers();
128 }
129 new_task->set_actual_size(_active_workers);
130 new_task->set_for_termination(_active_workers);
131
132 assert(_started_workers == 0, "Tabula rasa non");
133 assert(_finished_workers == 0, "Tabula rasa non");
134 assert(_yielded_workers == 0, "Tabula rasa non");
135 yielding_task()->set_status(ACTIVE);
136
137 // Wake up all the workers, the first few will get to work,
138 // and the rest will go back to sleep
139 monitor()->notify_all();
140 wait_for_gang();
141 }
142
143 void YieldingFlexibleWorkGang::wait_for_gang() {
144
145 assert(monitor()->owned_by_self(), "Data race");
146 // Wait for task to complete or yield
147 for (Status status = yielding_task()->status();
148 status != COMPLETED && status != YIELDED && status != ABORTED;
149 status = yielding_task()->status()) {
150 assert(started_workers() <= active_workers(), "invariant");
151 assert(finished_workers() <= active_workers(), "invariant");
152 assert(yielded_workers() <= active_workers(), "invariant");
153 monitor()->wait(Mutex::_no_safepoint_check_flag);
154 }
155 switch (yielding_task()->status()) {
156 case COMPLETED:
157 case ABORTED: {
158 assert(finished_workers() == active_workers(), "Inconsistent status");
159 assert(yielded_workers() == 0, "Invariant");
160 reset(); // for next task; gang<->task binding released
161 break;
162 }
163 case YIELDED: {
164 assert(yielded_workers() > 0, "Invariant");
165 assert(yielded_workers() + finished_workers() == active_workers(),
166 "Inconsistent counts");
167 break;
168 }
169 case ACTIVE:
170 case INACTIVE:
171 case COMPLETING:
172 case YIELDING:
173 case ABORTING:
174 default:
175 ShouldNotReachHere();
176 }
177 }
178
179 void YieldingFlexibleWorkGang::continue_task(
180 YieldingFlexibleGangTask* gang_task) {
181
182 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
183 assert(task() != NULL && task() == gang_task, "Incorrect usage");
184 assert(_started_workers == _active_workers, "Precondition");
185 assert(_yielded_workers > 0 && yielding_task()->status() == YIELDED,
186 "Else why are we calling continue_task()");
187 // Restart the yielded gang workers
188 yielding_task()->set_status(ACTIVE);
189 monitor()->notify_all();
190 wait_for_gang();
191 }
192
193 void YieldingFlexibleWorkGang::reset() {
194 _started_workers = 0;
195 _finished_workers = 0;
196 yielding_task()->set_gang(NULL);
197 _task = NULL; // unbind gang from task
198 }
199
200 void YieldingFlexibleWorkGang::yield() {
201 assert(task() != NULL, "Inconsistency; should have task binding");
202 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
203 assert(yielded_workers() < active_workers(), "Consistency check");
204 if (yielding_task()->status() == ABORTING) {
205 // Do not yield; we need to abort as soon as possible
206 // XXX NOTE: This can cause a performance pathology in the
207 // current implementation in Mustang, as of today, and
208 // pre-Mustang in that as soon as an overflow occurs,
209 // yields will not be honoured. The right way to proceed
210 // of course is to fix bug # TBF, so that abort's cause
211 // us to return at each potential yield point.
212 return;
213 }
214 if (++_yielded_workers + finished_workers() == active_workers()) {
215 yielding_task()->set_status(YIELDED);
216 monitor()->notify_all();
217 } else {
218 yielding_task()->set_status(YIELDING);
219 }
220
221 while (true) {
222 switch (yielding_task()->status()) {
223 case YIELDING:
224 case YIELDED: {
225 monitor()->wait(Mutex::_no_safepoint_check_flag);
226 break; // from switch
227 }
228 case ACTIVE:
229 case ABORTING:
230 case COMPLETING: {
231 assert(_yielded_workers > 0, "Else why am i here?");
232 _yielded_workers--;
233 return;
234 }
235 case INACTIVE:
236 case ABORTED:
237 case COMPLETED:
238 default: {
239 ShouldNotReachHere();
240 }
241 }
242 }
243 // Only return is from inside switch statement above
244 ShouldNotReachHere();
245 }
246
247 void YieldingFlexibleWorkGang::abort() {
248 assert(task() != NULL, "Inconsistency; should have task binding");
249 MutexLockerEx ml(monitor(), Mutex::_no_safepoint_check_flag);
250 assert(yielded_workers() < active_workers(), "Consistency check");
251 #ifndef PRODUCT
252 switch (yielding_task()->status()) {
253 // allowed states
254 case ACTIVE:
255 case ABORTING:
256 case COMPLETING:
257 case YIELDING:
258 break;
259 // not allowed states
260 case INACTIVE:
261 case ABORTED:
262 case COMPLETED:
263 case YIELDED:
264 default:
265 ShouldNotReachHere();
266 }
267 #endif // !PRODUCT
268 Status prev_status = yielding_task()->status();
269 yielding_task()->set_status(ABORTING);
270 if (prev_status == YIELDING) {
271 assert(yielded_workers() > 0, "Inconsistency");
272 // At least one thread has yielded, wake it up
273 // so it can go back to waiting stations ASAP.
274 monitor()->notify_all();
275 }
276 }
277
278 ///////////////////////////////
279 // YieldingFlexibleGangTask
280 ///////////////////////////////
281 void YieldingFlexibleGangTask::yield() {
282 assert(gang() != NULL, "No gang to signal");
283 gang()->yield();
284 }
285
286 void YieldingFlexibleGangTask::abort() {
287 assert(gang() != NULL, "No gang to signal");
288 gang()->abort();
289 }
290
291 ///////////////////////////////
292 // YieldingFlexibleGangWorker
293 ///////////////////////////////
294 void YieldingFlexibleGangWorker::loop() {
295 int previous_sequence_number = 0;
296 Monitor* gang_monitor = gang()->monitor();
297 MutexLockerEx ml(gang_monitor, Mutex::_no_safepoint_check_flag);
298 WorkData data;
299 int id;
300 while (true) {
301 // Check if there is work to do or if we have been asked
302 // to terminate
303 gang()->internal_worker_poll(&data);
304 if (data.terminate()) {
305 // We have been asked to terminate.
306 assert(gang()->task() == NULL, "No task binding");
307 // set_status(TERMINATED);
308 return;
309 } else if (data.task() != NULL &&
310 data.sequence_number() != previous_sequence_number) {
311 // There is work to be done.
312 // First check if we need to become active or if there
313 // are already the requisite number of workers
314 if (gang()->started_workers() == yf_gang()->active_workers()) {
315 // There are already enough workers, we do not need to
316 // to run; fall through and wait on monitor.
317 } else {
318 // We need to pitch in and do the work.
319 assert(gang()->started_workers() < yf_gang()->active_workers(),
320 "Unexpected state");
321 id = gang()->started_workers();
322 gang()->internal_note_start();
323 // Now, release the gang mutex and do the work.
324 {
325 MutexUnlockerEx mul(gang_monitor, Mutex::_no_safepoint_check_flag);
326 data.task()->work(id); // This might include yielding
327 }
328 // Reacquire monitor and note completion of this worker
329 gang()->internal_note_finish();
330 // Update status of task based on whether all workers have
331 // finished or some have yielded
332 assert(data.task() == gang()->task(), "Confused task binding");
333 if (gang()->finished_workers() == yf_gang()->active_workers()) {
334 switch (data.yf_task()->status()) {
335 case ABORTING: {
336 data.yf_task()->set_status(ABORTED);
337 break;
338 }
339 case ACTIVE:
340 case COMPLETING: {
341 data.yf_task()->set_status(COMPLETED);
342 break;
343 }
344 default:
345 ShouldNotReachHere();
346 }
347 gang_monitor->notify_all(); // Notify overseer
348 } else { // at least one worker is still working or yielded
349 assert(gang()->finished_workers() < yf_gang()->active_workers(),
350 "Counts inconsistent");
351 switch (data.yf_task()->status()) {
352 case ACTIVE: {
353 // first, but not only thread to complete
354 data.yf_task()->set_status(COMPLETING);
355 break;
356 }
357 case YIELDING: {
358 if (gang()->finished_workers() + yf_gang()->yielded_workers()
359 == yf_gang()->active_workers()) {
360 data.yf_task()->set_status(YIELDED);
361 gang_monitor->notify_all(); // notify overseer
362 }
363 break;
364 }
365 case ABORTING:
366 case COMPLETING: {
367 break; // nothing to do
368 }
369 default: // everything else: INACTIVE, YIELDED, ABORTED, COMPLETED
370 ShouldNotReachHere();
371 }
372 }
373 }
374 }
375 // Remember the sequence number
376 previous_sequence_number = data.sequence_number();
377 // Wait for more work
378 gang_monitor->wait(Mutex::_no_safepoint_check_flag);
379 }
380 }