3 * Worker threads for parallel and concurrent GC.
5 * Copyright 2001-2003 Ximian, Inc
6 * Copyright 2003-2010 Novell, Inc.
7 * Copyright (C) 2012 Xamarin Inc
9 * Licensed under the MIT license. See LICENSE file in the project root for full license information.
17 #include "mono/sgen/sgen-gc.h"
18 #include "mono/sgen/sgen-workers.h"
19 #include "mono/sgen/sgen-thread-pool.h"
20 #include "mono/utils/mono-membar.h"
21 #include "mono/sgen/sgen-client.h"
23 static WorkerContext worker_contexts [GENERATION_MAX];
26 * Allowed transitions:
28 * | from \ to | NOT WORKING | WORKING | WORK ENQUEUED |
29 * |--------------------+-------------+---------+---------------+
30 * | NOT WORKING | - | - | main / worker |
31 * | WORKING | worker | - | main / worker |
32 * | WORK ENQUEUED | - | worker | - |
34 * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
35 * least once. Only after looking at the queue will it go back to WORKING, and then,
36 * eventually, to NOT WORKING. After enqueuing work the main thread transitions the state
37 * to WORK ENQUEUED. Signalling the worker thread to wake up is only necessary if the old
38 * state was NOT WORKING.
47 #define SGEN_WORKER_MIN_SECTIONS_SIGNAL 4
49 static guint64 stat_workers_num_finished;
52 set_state (WorkerData *data, State old_state, State new_state)
54 SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
55 if (new_state == STATE_NOT_WORKING)
56 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
57 else if (new_state == STATE_WORKING)
58 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
60 return InterlockedCompareExchange (&data->state, new_state, old_state) == old_state;
64 state_is_working_or_enqueued (State state)
66 return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
70 sgen_workers_ensure_awake (WorkerContext *context)
73 gboolean need_signal = FALSE;
76 * All workers are awaken, make sure we reset the parallel context.
77 * We call this function only when starting the workers so nobody is running,
78 * or when the last worker is enqueuing preclean work. In both cases we can't
79 * have a worker working using a nopar context, which means it is safe.
81 context->idle_func_object_ops = (context->active_workers_num > 1) ? context->idle_func_object_ops_par : context->idle_func_object_ops_nopar;
82 context->workers_finished = FALSE;
84 for (i = 0; i < context->active_workers_num; i++) {
86 gboolean did_set_state;
89 old_state = context->workers_data [i].state;
91 if (old_state == STATE_WORK_ENQUEUED)
94 did_set_state = set_state (&context->workers_data [i], old_state, STATE_WORK_ENQUEUED);
96 if (did_set_state && old_state == STATE_NOT_WORKING)
97 context->workers_data [i].last_start = sgen_timestamp ();
98 } while (!did_set_state);
100 if (!state_is_working_or_enqueued (old_state))
105 sgen_thread_pool_idle_signal (context->thread_pool_context);
109 worker_try_finish (WorkerData *data)
113 WorkerContext *context = data->context;
114 gint64 last_start = data->last_start;
116 ++stat_workers_num_finished;
118 mono_os_mutex_lock (&context->finished_lock);
120 for (i = 0; i < context->active_workers_num; i++) {
121 if (state_is_working_or_enqueued (context->workers_data [i].state))
126 SgenWorkersFinishCallback callback = context->finish_callback;
127 SGEN_ASSERT (0, context->idle_func_object_ops == context->idle_func_object_ops_nopar, "Why are we finishing with parallel context");
128 /* We are the last one left. Enqueue preclean job if we have one and awake everybody */
129 SGEN_ASSERT (0, data->state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
131 context->finish_callback = NULL;
133 context->worker_awakenings = 0;
134 /* Make sure each worker has a chance of seeing the enqueued jobs */
135 sgen_workers_ensure_awake (context);
136 SGEN_ASSERT (0, data->state == STATE_WORK_ENQUEUED, "Why did we fail to set our own state to ENQUEUED");
139 * Log to be able to get the duration of normal concurrent M&S phase.
140 * Worker indexes are 1 based, since 0 is logically considered gc thread.
142 binary_protocol_worker_finish_stats (data - &context->workers_data [0] + 1, context->generation, context->forced_stop, data->major_scan_time, data->los_scan_time, data->total_time + sgen_timestamp () - last_start);
148 old_state = data->state;
150 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
151 if (old_state == STATE_WORK_ENQUEUED)
153 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
154 } while (!set_state (data, old_state, STATE_NOT_WORKING));
157 * If we are second to last to finish, we set the scan context to the non-parallel
158 * version so we can speed up the last worker. This helps us maintain same level
159 * of performance as non-parallel mode even if we fail to distribute work properly.
162 context->idle_func_object_ops = context->idle_func_object_ops_nopar;
164 context->workers_finished = TRUE;
165 mono_os_mutex_unlock (&context->finished_lock);
167 data->total_time += (sgen_timestamp () - last_start);
168 binary_protocol_worker_finish_stats (data - &context->workers_data [0] + 1, context->generation, context->forced_stop, data->major_scan_time, data->los_scan_time, data->total_time);
170 sgen_gray_object_queue_trim_free_list (&data->private_gray_queue);
174 mono_os_mutex_unlock (&context->finished_lock);
178 sgen_workers_enqueue_job (int generation, SgenThreadPoolJob *job, gboolean enqueue)
181 job->func (NULL, job);
182 sgen_thread_pool_job_free (job);
186 sgen_thread_pool_job_enqueue (worker_contexts [generation].thread_pool_context, job);
190 workers_get_work (WorkerData *data)
192 SgenMajorCollector *major = sgen_get_major_collector ();
193 SgenMinorCollector *minor = sgen_get_minor_collector ();
194 GrayQueueSection *section;
196 g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
197 g_assert (major->is_concurrent || minor->is_parallel);
199 section = sgen_section_gray_queue_dequeue (&data->context->workers_distribute_gray_queue);
201 sgen_gray_object_enqueue_section (&data->private_gray_queue, section, major->is_parallel);
205 /* Nobody to steal from */
206 g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
211 workers_steal_work (WorkerData *data)
213 SgenMajorCollector *major = sgen_get_major_collector ();
214 SgenMinorCollector *minor = sgen_get_minor_collector ();
215 int generation = sgen_get_current_collection_generation ();
216 GrayQueueSection *section = NULL;
217 WorkerContext *context = data->context;
218 int i, current_worker;
220 if ((generation == GENERATION_OLD && !major->is_parallel) ||
221 (generation == GENERATION_NURSERY && !minor->is_parallel))
224 /* If we're parallel, steal from other workers' private gray queues */
225 g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
227 current_worker = (int) (data - context->workers_data);
229 for (i = 1; i < context->active_workers_num && !section; i++) {
230 int steal_worker = (current_worker + i) % context->active_workers_num;
231 if (state_is_working_or_enqueued (context->workers_data [steal_worker].state))
232 section = sgen_gray_object_steal_section (&context->workers_data [steal_worker].private_gray_queue);
236 sgen_gray_object_enqueue_section (&data->private_gray_queue, section, TRUE);
240 /* Nobody to steal from */
241 g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
246 concurrent_enqueue_check (GCObject *obj)
248 g_assert (sgen_concurrent_collection_in_progress ());
249 g_assert (!sgen_ptr_in_nursery (obj));
250 g_assert (SGEN_LOAD_VTABLE (obj));
254 init_private_gray_queue (WorkerData *data)
256 sgen_gray_object_queue_init (&data->private_gray_queue,
257 sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL,
262 thread_pool_init_func (void *data_untyped)
264 WorkerData *data = (WorkerData *)data_untyped;
265 SgenMajorCollector *major = sgen_get_major_collector ();
266 SgenMinorCollector *minor = sgen_get_minor_collector ();
268 if (!major->is_concurrent && !minor->is_parallel)
271 init_private_gray_queue (data);
273 /* Separate WorkerData for same thread share free_block_lists */
274 if (major->is_parallel || minor->is_parallel)
275 major->init_block_free_lists (&data->free_block_lists);
279 sgen_workers_are_working (WorkerContext *context)
283 for (i = 0; i < context->active_workers_num; i++) {
284 if (state_is_working_or_enqueued (context->workers_data [i].state))
291 continue_idle_func (void *data_untyped, int thread_pool_context)
294 return state_is_working_or_enqueued (((WorkerData*)data_untyped)->state);
296 /* Return if any of the threads is working in the context */
297 if (worker_contexts [GENERATION_NURSERY].workers_num && worker_contexts [GENERATION_NURSERY].thread_pool_context == thread_pool_context)
298 return sgen_workers_are_working (&worker_contexts [GENERATION_NURSERY]);
299 if (worker_contexts [GENERATION_OLD].workers_num && worker_contexts [GENERATION_OLD].thread_pool_context == thread_pool_context)
300 return sgen_workers_are_working (&worker_contexts [GENERATION_OLD]);
302 g_assert_not_reached ();
307 should_work_func (void *data_untyped)
309 WorkerData *data = (WorkerData*)data_untyped;
310 WorkerContext *context = data->context;
311 int current_worker = (int) (data - context->workers_data);
313 return context->started && current_worker < context->active_workers_num && state_is_working_or_enqueued (data->state);
317 marker_idle_func (void *data_untyped)
319 WorkerData *data = (WorkerData *)data_untyped;
320 WorkerContext *context = data->context;
322 SGEN_ASSERT (0, continue_idle_func (data_untyped, context->thread_pool_context), "Why are we called when we're not supposed to work?");
324 if (data->state == STATE_WORK_ENQUEUED) {
325 set_state (data, STATE_WORK_ENQUEUED, STATE_WORKING);
326 SGEN_ASSERT (0, data->state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
329 if (!context->forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data) || workers_steal_work (data))) {
330 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (context->idle_func_object_ops, &data->private_gray_queue);
332 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
334 sgen_drain_gray_stack (ctx);
336 if (data->private_gray_queue.num_sections >= SGEN_WORKER_MIN_SECTIONS_SIGNAL
337 && context->workers_finished && context->worker_awakenings < context->active_workers_num) {
338 /* We bound the number of worker awakenings just to be sure */
339 context->worker_awakenings++;
340 mono_os_mutex_lock (&context->finished_lock);
341 sgen_workers_ensure_awake (context);
342 mono_os_mutex_unlock (&context->finished_lock);
345 worker_try_finish (data);
350 init_distribute_gray_queue (WorkerContext *context)
352 sgen_section_gray_queue_init (&context->workers_distribute_gray_queue, TRUE,
353 sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
357 sgen_workers_create_context (int generation, int num_workers)
359 static gboolean stat_inited = FALSE;
361 WorkerData **workers_data_ptrs = (WorkerData**)sgen_alloc_internal_dynamic (num_workers * sizeof(WorkerData*), INTERNAL_MEM_WORKER_DATA, TRUE);
362 WorkerContext *context = &worker_contexts [generation];
364 SGEN_ASSERT (0, !context->workers_num, "We can't init the worker context for a generation twice");
366 mono_os_mutex_init (&context->finished_lock);
368 context->generation = generation;
369 context->workers_num = num_workers;
370 context->active_workers_num = num_workers;
372 context->workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
373 memset (context->workers_data, 0, sizeof (WorkerData) * num_workers);
375 init_distribute_gray_queue (context);
377 for (i = 0; i < num_workers; ++i) {
378 workers_data_ptrs [i] = &context->workers_data [i];
379 context->workers_data [i].context = context;
382 context->thread_pool_context = sgen_thread_pool_create_context (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, should_work_func, (void**)workers_data_ptrs);
385 mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
390 /* This is called with thread pool lock so no context switch can happen */
392 continue_idle_wait (int calling_context, int *threads_context)
394 WorkerContext *context;
397 if (worker_contexts [GENERATION_OLD].workers_num && calling_context == worker_contexts [GENERATION_OLD].thread_pool_context)
398 context = &worker_contexts [GENERATION_OLD];
399 else if (worker_contexts [GENERATION_NURSERY].workers_num && calling_context == worker_contexts [GENERATION_NURSERY].thread_pool_context)
400 context = &worker_contexts [GENERATION_NURSERY];
402 g_assert_not_reached ();
405 * We assume there are no pending jobs, since this is called only after
406 * we waited for all the jobs.
408 for (i = 0; i < context->active_workers_num; i++) {
409 if (threads_context [i] == calling_context)
413 if (sgen_workers_have_idle_work (context->generation) && !context->forced_stop)
417 * At this point there are no jobs to be done, and no objects to be scanned
418 * in the gray queues. We can simply asynchronously finish all the workers
419 * from the context that were not finished already (due to being stuck working
420 * in another context)
423 for (i = 0; i < context->active_workers_num; i++) {
424 if (context->workers_data [i].state == STATE_WORK_ENQUEUED)
425 set_state (&context->workers_data [i], STATE_WORK_ENQUEUED, STATE_WORKING);
426 if (context->workers_data [i].state == STATE_WORKING)
427 worker_try_finish (&context->workers_data [i]);
435 sgen_workers_stop_all_workers (int generation)
437 WorkerContext *context = &worker_contexts [generation];
439 mono_os_mutex_lock (&context->finished_lock);
440 context->finish_callback = NULL;
441 mono_os_mutex_unlock (&context->finished_lock);
443 context->forced_stop = TRUE;
445 sgen_thread_pool_wait_for_all_jobs (context->thread_pool_context);
446 sgen_thread_pool_idle_wait (context->thread_pool_context, continue_idle_wait);
447 SGEN_ASSERT (0, !sgen_workers_are_working (context), "Can only signal enqueue work when in no work state");
449 context->started = FALSE;
453 sgen_workers_set_num_active_workers (int generation, int num_workers)
455 WorkerContext *context = &worker_contexts [generation];
457 SGEN_ASSERT (0, num_workers <= context->workers_num, "We can't start more workers than we initialized");
458 context->active_workers_num = num_workers;
460 context->active_workers_num = context->workers_num;
465 sgen_workers_start_all_workers (int generation, SgenObjectOperations *object_ops_nopar, SgenObjectOperations *object_ops_par, SgenWorkersFinishCallback callback)
467 WorkerContext *context = &worker_contexts [generation];
469 SGEN_ASSERT (0, !context->started, "Why are we starting to work without finishing previous cycle");
471 context->idle_func_object_ops_par = object_ops_par;
472 context->idle_func_object_ops_nopar = object_ops_nopar;
473 context->forced_stop = FALSE;
474 context->finish_callback = callback;
475 context->worker_awakenings = 0;
476 context->started = TRUE;
478 for (i = 0; i < context->active_workers_num; i++) {
479 context->workers_data [i].major_scan_time = 0;
480 context->workers_data [i].los_scan_time = 0;
481 context->workers_data [i].total_time = 0;
482 context->workers_data [i].last_start = 0;
484 mono_memory_write_barrier ();
487 * We expect workers to start finishing only after all of them were awaken.
488 * Otherwise we might think that we have fewer workers and use wrong context.
490 mono_os_mutex_lock (&context->finished_lock);
491 sgen_workers_ensure_awake (context);
492 mono_os_mutex_unlock (&context->finished_lock);
496 sgen_workers_join (int generation)
498 WorkerContext *context = &worker_contexts [generation];
501 SGEN_ASSERT (0, !context->finish_callback, "Why are we joining concurrent mark early");
503 sgen_thread_pool_wait_for_all_jobs (context->thread_pool_context);
504 sgen_thread_pool_idle_wait (context->thread_pool_context, continue_idle_wait);
505 SGEN_ASSERT (0, !sgen_workers_are_working (context), "Can only signal enqueue work when in no work state");
507 /* At this point all the workers have stopped. */
509 SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&context->workers_distribute_gray_queue), "Why is there still work left to do?");
510 for (i = 0; i < context->active_workers_num; ++i)
511 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&context->workers_data [i].private_gray_queue), "Why is there still work left to do?");
513 context->started = FALSE;
517 * Can only be called if the workers are not working in the
518 * context and there are no pending jobs.
521 sgen_workers_have_idle_work (int generation)
523 WorkerContext *context = &worker_contexts [generation];
526 if (!sgen_section_gray_queue_is_empty (&context->workers_distribute_gray_queue))
529 for (i = 0; i < context->active_workers_num; ++i) {
530 if (!sgen_gray_object_queue_is_empty (&context->workers_data [i].private_gray_queue))
538 sgen_workers_all_done (void)
540 if (worker_contexts [GENERATION_NURSERY].workers_num && sgen_workers_are_working (&worker_contexts [GENERATION_NURSERY]))
542 if (worker_contexts [GENERATION_OLD].workers_num && sgen_workers_are_working (&worker_contexts [GENERATION_OLD]))
549 sgen_workers_assert_gray_queue_is_empty (int generation)
551 SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&worker_contexts [generation].workers_distribute_gray_queue), "Why is the workers gray queue not empty?");
555 sgen_workers_take_from_queue (int generation, SgenGrayQueue *queue)
557 WorkerContext *context = &worker_contexts [generation];
559 sgen_gray_object_spread (queue, sgen_workers_get_job_split_count (generation));
562 GrayQueueSection *section = sgen_gray_object_dequeue_section (queue);
565 sgen_section_gray_queue_enqueue (&context->workers_distribute_gray_queue, section);
568 SGEN_ASSERT (0, !sgen_workers_are_working (context), "We should fully populate the distribute gray queue before we start the workers");
571 SgenObjectOperations*
572 sgen_workers_get_idle_func_object_ops (WorkerData *worker)
574 g_assert (worker->context->idle_func_object_ops);
575 return worker->context->idle_func_object_ops;
579 * If we have a single worker, splitting into multiple jobs makes no sense. With
580 * more than one worker, we split into a larger number of jobs so that, in case
581 * the work load is uneven, a worker that finished quickly can take up more jobs
584 * We also return 1 if there is no worker context for that generation.
587 sgen_workers_get_job_split_count (int generation)
589 return (worker_contexts [generation].active_workers_num > 1) ? worker_contexts [generation].active_workers_num * 4 : 1;
593 sgen_workers_foreach (int generation, SgenWorkerCallback callback)
595 WorkerContext *context = &worker_contexts [generation];
598 for (i = 0; i < context->workers_num; i++)
599 callback (&context->workers_data [i]);
603 sgen_workers_is_worker_thread (MonoNativeThreadId id)
605 return sgen_thread_pool_is_thread_pool_thread (id);