2 * sgen-workers.c: Worker threads for parallel and concurrent GC.
4 * Copyright 2001-2003 Ximian, Inc
5 * Copyright 2003-2010 Novell, Inc.
6 * Copyright (C) 2012 Xamarin Inc
8 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
16 #include "mono/sgen/sgen-gc.h"
17 #include "mono/sgen/sgen-workers.h"
18 #include "mono/sgen/sgen-thread-pool.h"
19 #include "mono/utils/mono-membar.h"
20 #include "mono/sgen/sgen-client.h"
22 static int workers_num;
23 static volatile gboolean forced_stop;
24 static WorkerData *workers_data;
27 * When using multiple workers, we need to have the last worker
28 * enqueue the preclean jobs (if there are any). This lock ensures
29 * that when the last worker takes it, all the other workers have
30 * gracefully finished, so it can restart them.
32 static mono_mutex_t finished_lock;
34 static SgenSectionGrayQueue workers_distribute_gray_queue;
35 static gboolean workers_distribute_gray_queue_inited;
38 * Allowed transitions:
40 * | from \ to | NOT WORKING | WORKING | WORK ENQUEUED |
41 * |--------------------+-------------+---------+---------------+
42 * | NOT WORKING | - | - | main / worker |
43 * | WORKING | worker | - | main / worker |
44 * | WORK ENQUEUED | - | worker | - |
46 * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
47 * least once. Only after looking at the queue will it go back to WORKING, and then,
48 * eventually, to NOT WORKING. After enqueuing work the main thread transitions the state
49 * to WORK ENQUEUED. Signalling the worker thread to wake up is only necessary if the old
50 * state was NOT WORKING.
61 static SgenObjectOperations * volatile idle_func_object_ops;
63 * finished_callback is called only when the workers finish work normally (when they
64 * are not forced to finish). The callback is used to enqueue preclean jobs.
66 static volatile SgenWorkersFinishCallback finish_callback;
68 static guint64 stat_workers_num_finished;
71 set_state (WorkerData *data, State old_state, State new_state)
73 SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
74 if (new_state == STATE_NOT_WORKING)
75 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
76 else if (new_state == STATE_WORKING)
77 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
78 if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
79 SGEN_ASSERT (6, sgen_thread_pool_is_thread_pool_thread (mono_native_thread_id_get ()), "Only the worker thread is allowed to transition to NOT_WORKING or WORKING");
81 return InterlockedCompareExchange (&data->state, new_state, old_state) == old_state;
85 state_is_working_or_enqueued (State state)
87 return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
91 sgen_workers_ensure_awake (void)
94 gboolean need_signal = FALSE;
96 for (i = 0; i < workers_num; i++) {
98 gboolean did_set_state;
101 old_state = workers_data [i].state;
103 if (old_state == STATE_WORK_ENQUEUED)
106 did_set_state = set_state (&workers_data [i], old_state, STATE_WORK_ENQUEUED);
107 } while (!did_set_state);
109 if (!state_is_working_or_enqueued (old_state))
114 sgen_thread_pool_idle_signal ();
118 worker_try_finish (WorkerData *data)
123 ++stat_workers_num_finished;
125 mono_os_mutex_lock (&finished_lock);
127 for (i = 0; i < workers_num; i++) {
128 if (state_is_working_or_enqueued (workers_data [i].state))
133 SgenWorkersFinishCallback callback = finish_callback;
134 /* We are the last one left. Enqueue preclean job if we have one and awake everybody */
135 SGEN_ASSERT (0, data->state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
137 finish_callback = NULL;
139 /* Make sure each worker has a chance of seeing the enqueued jobs */
140 sgen_workers_ensure_awake ();
141 SGEN_ASSERT (0, data->state == STATE_WORK_ENQUEUED, "Why did we fail to set our own state to ENQUEUED");
147 old_state = data->state;
149 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
150 if (old_state == STATE_WORK_ENQUEUED)
152 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
153 } while (!set_state (data, old_state, STATE_NOT_WORKING));
155 mono_os_mutex_unlock (&finished_lock);
157 binary_protocol_worker_finish (sgen_timestamp (), forced_stop);
159 sgen_gray_object_queue_trim_free_list (&data->private_gray_queue);
163 mono_os_mutex_unlock (&finished_lock);
167 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
170 job->func (NULL, job);
171 sgen_thread_pool_job_free (job);
175 sgen_thread_pool_job_enqueue (job);
179 sgen_workers_wait_for_jobs_finished (void)
181 sgen_thread_pool_wait_for_all_jobs ();
183 * If the idle task was never triggered or it finished before the last job did and
184 * then didn't get triggered again, we might end up in the situation of having
185 * something in the gray queue yet the idle task not working. The easiest way to
186 * make sure this doesn't stay that way is to just trigger it again after all jobs
189 sgen_workers_ensure_awake ();
193 workers_get_work (WorkerData *data)
195 SgenMajorCollector *major;
197 g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
199 /* If we're concurrent, steal from the workers distribute gray queue. */
200 major = sgen_get_major_collector ();
201 if (major->is_concurrent) {
202 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
204 sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
209 /* Nobody to steal from */
210 g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
215 concurrent_enqueue_check (GCObject *obj)
217 g_assert (sgen_concurrent_collection_in_progress ());
218 g_assert (!sgen_ptr_in_nursery (obj));
219 g_assert (SGEN_LOAD_VTABLE (obj));
223 init_private_gray_queue (WorkerData *data)
225 sgen_gray_object_queue_init (&data->private_gray_queue,
226 sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL,
231 thread_pool_init_func (void *data_untyped)
233 WorkerData *data = (WorkerData *)data_untyped;
234 SgenMajorCollector *major = sgen_get_major_collector ();
236 sgen_client_thread_register_worker ();
238 if (!major->is_concurrent)
241 init_private_gray_queue (data);
245 continue_idle_func (void *data_untyped)
248 WorkerData *data = (WorkerData *)data_untyped;
249 return state_is_working_or_enqueued (data->state);
251 /* Return if any of the threads is working */
252 return !sgen_workers_all_done ();
257 marker_idle_func (void *data_untyped)
259 WorkerData *data = (WorkerData *)data_untyped;
261 SGEN_ASSERT (0, continue_idle_func (data_untyped), "Why are we called when we're not supposed to work?");
262 SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
264 if (data->state == STATE_WORK_ENQUEUED) {
265 set_state (data, STATE_WORK_ENQUEUED, STATE_WORKING);
266 SGEN_ASSERT (0, data->state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
269 if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data))) {
270 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
272 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
274 sgen_drain_gray_stack (ctx);
276 worker_try_finish (data);
281 init_distribute_gray_queue (void)
283 if (workers_distribute_gray_queue_inited) {
284 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
285 g_assert (workers_distribute_gray_queue.locked);
289 sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
290 sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
291 workers_distribute_gray_queue_inited = TRUE;
295 sgen_workers_init_distribute_gray_queue (void)
297 SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent,
298 "Why should we init the distribute gray queue if we don't need it?");
299 init_distribute_gray_queue ();
303 sgen_workers_init (int num_workers)
306 void **workers_data_ptrs = (void **)alloca(num_workers * sizeof(void *));
308 if (!sgen_get_major_collector ()->is_concurrent) {
309 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
313 mono_os_mutex_init (&finished_lock);
314 //g_print ("initing %d workers\n", num_workers);
316 workers_num = num_workers;
318 workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
319 memset (workers_data, 0, sizeof (WorkerData) * num_workers);
321 init_distribute_gray_queue ();
323 for (i = 0; i < num_workers; ++i)
324 workers_data_ptrs [i] = (void *) &workers_data [i];
326 sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
328 mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
332 sgen_workers_stop_all_workers (void)
334 finish_callback = NULL;
335 mono_memory_write_barrier ();
338 sgen_thread_pool_wait_for_all_jobs ();
339 sgen_thread_pool_idle_wait ();
340 SGEN_ASSERT (0, sgen_workers_all_done (), "Can only signal enqueue work when in no work state");
344 sgen_workers_start_all_workers (SgenObjectOperations *object_ops, SgenWorkersFinishCallback callback)
347 idle_func_object_ops = object_ops;
348 finish_callback = callback;
349 mono_memory_write_barrier ();
351 sgen_workers_ensure_awake ();
355 sgen_workers_join (void)
359 sgen_thread_pool_wait_for_all_jobs ();
360 sgen_thread_pool_idle_wait ();
361 SGEN_ASSERT (0, sgen_workers_all_done (), "Can only signal enqueue work when in no work state");
363 /* At this point all the workers have stopped. */
365 SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
366 for (i = 0; i < workers_num; ++i)
367 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
371 * Can only be called if the workers are stopped.
372 * If we're stopped, there are also no pending jobs.
375 sgen_workers_have_idle_work (void)
379 SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
381 if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
384 for (i = 0; i < workers_num; ++i) {
385 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
393 sgen_workers_all_done (void)
397 for (i = 0; i < workers_num; i++) {
398 if (state_is_working_or_enqueued (workers_data [i].state))
404 /* Must only be used for debugging */
406 sgen_workers_are_working (void)
408 return !sgen_workers_all_done ();
412 sgen_workers_assert_gray_queue_is_empty (void)
414 SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is the workers gray queue not empty?");
418 sgen_workers_take_from_queue_and_awake (SgenGrayQueue *queue)
420 gboolean wake = FALSE;
423 GrayQueueSection *section = sgen_gray_object_dequeue_section (queue);
426 sgen_section_gray_queue_enqueue (&workers_distribute_gray_queue, section);
431 SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "Why is there work to take when there's no concurrent collection in progress?");
432 sgen_workers_ensure_awake ();
436 SgenObjectOperations*
437 sgen_workers_get_idle_func_object_ops (void)
439 return idle_func_object_ops;
443 * If we have a single worker, splitting into multiple jobs makes no sense. With
444 * more than one worker, we split into a larger number of jobs so that, in case
445 * the work load is uneven, a worker that finished quickly can take up more jobs
449 sgen_workers_get_job_split_count (void)
451 return (workers_num > 1) ? workers_num * 4 : 1;