mono/sgen/sgen-workers.c

   1 /*
   2  * sgen-workers.c: Worker threads for parallel and concurrent GC.
   3  *
   4  * Copyright 2001-2003 Ximian, Inc
   5  * Copyright 2003-2010 Novell, Inc.
   6  * Copyright (C) 2012 Xamarin Inc
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Library General Public
  10  * License 2.0 as published by the Free Software Foundation;
  11  *
  12  * This library is distributed in the hope that it will be useful,
  13  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15  * Library General Public License for more details.
  16  *
  17  * You should have received a copy of the GNU Library General Public
  18  * License 2.0 along with this library; if not, write to the Free
  19  * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  20  */
  21
  22 #include "config.h"
  23 #ifdef HAVE_SGEN_GC
  24
  25 #include <string.h>
  26
  27 #include "mono/sgen/sgen-gc.h"
  28 #include "mono/sgen/sgen-workers.h"
  29 #include "mono/sgen/sgen-thread-pool.h"
  30 #include "mono/utils/mono-membar.h"
  31 #include "mono/sgen/sgen-client.h"
  32
  33 static int workers_num;
  34 static WorkerData *workers_data;
  35
  36 static SgenSectionGrayQueue workers_distribute_gray_queue;
  37 static gboolean workers_distribute_gray_queue_inited;
  38
  39 /*
  40  * Allowed transitions:
  41  *
  42  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED |
  43  * |--------------------+-------------+---------+---------------+
  44  * | NOT WORKING        | -           | -       | main          |
  45  * | WORKING            | worker      | -       | main          |
  46  * | WORK ENQUEUED      | -           | worker  | -             |
  47  *
  48  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  49  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  50  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  51  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  52  * state was NOT WORKING.
  53  */
  54
  55 enum {
  56         STATE_NOT_WORKING,
  57         STATE_WORKING,
  58         STATE_WORK_ENQUEUED
  59 };
  60
  61 typedef gint32 State;
  62
  63 static volatile State workers_state;
  64
  65 static SgenObjectOperations * volatile idle_func_object_ops;
  66
  67 static guint64 stat_workers_num_finished;
  68
  69 static gboolean
  70 set_state (State old_state, State new_state)
  71 {
  72         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  73         if (new_state == STATE_NOT_WORKING)
  74                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  75         else if (new_state == STATE_WORKING)
  76                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  77         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  78                 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");
  79
  80         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  81 }
  82
  83 static gboolean
  84 state_is_working_or_enqueued (State state)
  85 {
  86         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  87 }
  88
  89 void
  90 sgen_workers_ensure_awake (void)
  91 {
  92         State old_state;
  93         gboolean did_set_state;
  94
  95         do {
  96                 old_state = workers_state;
  97
  98                 if (old_state == STATE_WORK_ENQUEUED)
  99                         break;
 100
 101                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
 102         } while (!did_set_state);
 103
 104         if (!state_is_working_or_enqueued (old_state))
 105                 sgen_thread_pool_idle_signal ();
 106 }
 107
 108 static void
 109 worker_try_finish (void)
 110 {
 111         State old_state;
 112
 113         ++stat_workers_num_finished;
 114
 115         do {
 116                 old_state = workers_state;
 117
 118                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 119                 if (old_state == STATE_WORK_ENQUEUED)
 120                         return;
 121                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 122
 123                 /* We are the last thread to go to sleep. */
 124         } while (!set_state (old_state, STATE_NOT_WORKING));
 125 }
 126
 127 static gboolean
 128 collection_needs_workers (void)
 129 {
 130         return sgen_collection_is_concurrent ();
 131 }
 132
 133 void
 134 sgen_workers_enqueue_job (SgenThreadPoolJob *job)
 135 {
 136         if (!collection_needs_workers ()) {
 137                 job->func (NULL, job);
 138                 sgen_thread_pool_job_free (job);
 139                 return;
 140         }
 141
 142         sgen_thread_pool_job_enqueue (job);
 143 }
 144
 145 void
 146 sgen_workers_wait_for_jobs_finished (void)
 147 {
 148         sgen_thread_pool_wait_for_all_jobs ();
 149         /*
 150          * If the idle task was never triggered or it finished before the last job did and
 151          * then didn't get triggered again, we might end up in the situation of having
 152          * something in the gray queue yet the idle task not working.  The easiest way to
 153          * make sure this doesn't stay that way is to just trigger it again after all jobs
 154          * have finished.
 155          */
 156         sgen_workers_ensure_awake ();
 157 }
 158
 159 static gboolean
 160 workers_get_work (WorkerData *data)
 161 {
 162         SgenMajorCollector *major;
 163
 164         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 165
 166         /* If we're concurrent, steal from the workers distribute gray queue. */
 167         major = sgen_get_major_collector ();
 168         if (major->is_concurrent) {
 169                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 170                 if (section) {
 171                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 172                         return TRUE;
 173                 }
 174         }
 175
 176         /* Nobody to steal from */
 177         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 178         return FALSE;
 179 }
 180
 181 static void
 182 concurrent_enqueue_check (GCObject *obj)
 183 {
 184         g_assert (sgen_concurrent_collection_in_progress ());
 185         g_assert (!sgen_ptr_in_nursery (obj));
 186         g_assert (SGEN_LOAD_VTABLE (obj));
 187 }
 188
 189 static void
 190 init_private_gray_queue (WorkerData *data)
 191 {
 192         sgen_gray_object_queue_init (&data->private_gray_queue,
 193                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 194 }
 195
 196 static void
 197 thread_pool_init_func (void *data_untyped)
 198 {
 199         WorkerData *data = data_untyped;
 200         SgenMajorCollector *major = sgen_get_major_collector ();
 201
 202         sgen_client_thread_register_worker ();
 203
 204         if (!major->is_concurrent)
 205                 return;
 206
 207         init_private_gray_queue (data);
 208 }
 209
 210 static gboolean
 211 continue_idle_func (void)
 212 {
 213         return state_is_working_or_enqueued (workers_state);
 214 }
 215
 216 static void
 217 marker_idle_func (void *data_untyped)
 218 {
 219         WorkerData *data = data_untyped;
 220
 221         SGEN_ASSERT (0, continue_idle_func (), "Why are we called when we're not supposed to work?");
 222         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 223
 224         if (workers_state == STATE_WORK_ENQUEUED) {
 225                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 226                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 227         }
 228
 229         if (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data)) {
 230                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 231
 232                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 233
 234                 sgen_drain_gray_stack (32, ctx);
 235         } else {
 236                 worker_try_finish ();
 237         }
 238 }
 239
 240 static void
 241 init_distribute_gray_queue (void)
 242 {
 243         if (workers_distribute_gray_queue_inited) {
 244                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 245                 g_assert (workers_distribute_gray_queue.locked);
 246                 return;
 247         }
 248
 249         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 250                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 251         workers_distribute_gray_queue_inited = TRUE;
 252 }
 253
 254 void
 255 sgen_workers_init_distribute_gray_queue (void)
 256 {
 257         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent && collection_needs_workers (),
 258                         "Why should we init the distribute gray queue if we don't need it?");
 259         init_distribute_gray_queue ();
 260 }
 261
 262 void
 263 sgen_workers_init (int num_workers)
 264 {
 265         int i;
 266         void **workers_data_ptrs = alloca(num_workers * sizeof(void *));
 267
 268         if (!sgen_get_major_collector ()->is_concurrent) {
 269                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 270                 return;
 271         }
 272
 273         //g_print ("initing %d workers\n", num_workers);
 274
 275         workers_num = num_workers;
 276
 277         workers_data = sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 278         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 279
 280         init_distribute_gray_queue ();
 281
 282         for (i = 0; i < workers_num; ++i)
 283                 workers_data_ptrs [i] = (void *) &workers_data [i];
 284
 285         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 286
 287         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 288 }
 289
 290 void
 291 sgen_workers_start_all_workers (SgenObjectOperations *object_ops)
 292 {
 293         if (!collection_needs_workers ())
 294                 return;
 295
 296         idle_func_object_ops = object_ops;
 297         mono_memory_write_barrier ();
 298
 299         sgen_workers_ensure_awake ();
 300 }
 301
 302 void
 303 sgen_workers_join (void)
 304 {
 305         int i;
 306
 307         if (!collection_needs_workers ())
 308                 return;
 309
 310         sgen_thread_pool_wait_for_all_jobs ();
 311         sgen_thread_pool_idle_wait ();
 312         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 313
 314         /* At this point all the workers have stopped. */
 315
 316         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 317         for (i = 0; i < workers_num; ++i)
 318                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 319 }
 320
 321 gboolean
 322 sgen_workers_all_done (void)
 323 {
 324         return workers_state == STATE_NOT_WORKING;
 325 }
 326
 327 /* Must only be used for debugging */
 328 gboolean
 329 sgen_workers_are_working (void)
 330 {
 331         return state_is_working_or_enqueued (workers_state);
 332 }
 333
 334 void
 335 sgen_workers_wait (void)
 336 {
 337         sgen_thread_pool_idle_wait ();
 338         SGEN_ASSERT (0, sgen_workers_all_done (), "Why are the workers not done after we wait for them?");
 339 }
 340
 341 SgenSectionGrayQueue*
 342 sgen_workers_get_distribute_section_gray_queue (void)
 343 {
 344         return &workers_distribute_gray_queue;
 345 }
 346
 347 #endif