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 volatile gboolean forced_stop;
  35 static WorkerData *workers_data;
  36
  37 static SgenSectionGrayQueue workers_distribute_gray_queue;
  38 static gboolean workers_distribute_gray_queue_inited;
  39
  40 /*
  41  * Allowed transitions:
  42  *
  43  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED |
  44  * |--------------------+-------------+---------+---------------+
  45  * | NOT WORKING        | -           | -       | main          |
  46  * | WORKING            | worker      | -       | main          |
  47  * | WORK ENQUEUED      | -           | worker  | -             |
  48  *
  49  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  50  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  51  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  52  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  53  * state was NOT WORKING.
  54  */
  55
  56 enum {
  57         STATE_NOT_WORKING,
  58         STATE_WORKING,
  59         STATE_WORK_ENQUEUED
  60 };
  61
  62 typedef gint32 State;
  63
  64 static volatile State workers_state;
  65
  66 static SgenObjectOperations * volatile idle_func_object_ops;
  67
  68 static guint64 stat_workers_num_finished;
  69
  70 static gboolean
  71 set_state (State old_state, State new_state)
  72 {
  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");
  80
  81         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  82 }
  83
  84 static gboolean
  85 state_is_working_or_enqueued (State state)
  86 {
  87         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  88 }
  89
  90 void
  91 sgen_workers_ensure_awake (void)
  92 {
  93         State old_state;
  94         gboolean did_set_state;
  95
  96         do {
  97                 old_state = workers_state;
  98
  99                 if (old_state == STATE_WORK_ENQUEUED)
 100                         break;
 101
 102                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
 103         } while (!did_set_state);
 104
 105         if (!state_is_working_or_enqueued (old_state))
 106                 sgen_thread_pool_idle_signal ();
 107 }
 108
 109 static void
 110 worker_try_finish (void)
 111 {
 112         State old_state;
 113
 114         ++stat_workers_num_finished;
 115
 116         do {
 117                 old_state = workers_state;
 118
 119                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 120                 if (old_state == STATE_WORK_ENQUEUED)
 121                         return;
 122                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 123
 124                 /* We are the last thread to go to sleep. */
 125         } while (!set_state (old_state, STATE_NOT_WORKING));
 126
 127         binary_protocol_worker_finish (sgen_timestamp (), forced_stop);
 128 }
 129
 130 void
 131 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
 132 {
 133         if (!enqueue) {
 134                 job->func (NULL, job);
 135                 sgen_thread_pool_job_free (job);
 136                 return;
 137         }
 138
 139         sgen_thread_pool_job_enqueue (job);
 140 }
 141
 142 void
 143 sgen_workers_wait_for_jobs_finished (void)
 144 {
 145         sgen_thread_pool_wait_for_all_jobs ();
 146         /*
 147          * If the idle task was never triggered or it finished before the last job did and
 148          * then didn't get triggered again, we might end up in the situation of having
 149          * something in the gray queue yet the idle task not working.  The easiest way to
 150          * make sure this doesn't stay that way is to just trigger it again after all jobs
 151          * have finished.
 152          */
 153         sgen_workers_ensure_awake ();
 154 }
 155
 156 static gboolean
 157 workers_get_work (WorkerData *data)
 158 {
 159         SgenMajorCollector *major;
 160
 161         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 162
 163         /* If we're concurrent, steal from the workers distribute gray queue. */
 164         major = sgen_get_major_collector ();
 165         if (major->is_concurrent) {
 166                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 167                 if (section) {
 168                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 169                         return TRUE;
 170                 }
 171         }
 172
 173         /* Nobody to steal from */
 174         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 175         return FALSE;
 176 }
 177
 178 static void
 179 concurrent_enqueue_check (GCObject *obj)
 180 {
 181         g_assert (sgen_concurrent_collection_in_progress ());
 182         g_assert (!sgen_ptr_in_nursery (obj));
 183         g_assert (SGEN_LOAD_VTABLE (obj));
 184 }
 185
 186 static void
 187 init_private_gray_queue (WorkerData *data)
 188 {
 189         sgen_gray_object_queue_init (&data->private_gray_queue,
 190                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 191 }
 192
 193 static void
 194 thread_pool_init_func (void *data_untyped)
 195 {
 196         WorkerData *data = (WorkerData *)data_untyped;
 197         SgenMajorCollector *major = sgen_get_major_collector ();
 198
 199         sgen_client_thread_register_worker ();
 200
 201         if (!major->is_concurrent)
 202                 return;
 203
 204         init_private_gray_queue (data);
 205 }
 206
 207 static gboolean
 208 continue_idle_func (void)
 209 {
 210         return state_is_working_or_enqueued (workers_state);
 211 }
 212
 213 static void
 214 marker_idle_func (void *data_untyped)
 215 {
 216         WorkerData *data = (WorkerData *)data_untyped;
 217
 218         SGEN_ASSERT (0, continue_idle_func (), "Why are we called when we're not supposed to work?");
 219         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 220
 221         if (workers_state == STATE_WORK_ENQUEUED) {
 222                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 223                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 224         }
 225
 226         if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data))) {
 227                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 228
 229                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 230
 231                 sgen_drain_gray_stack (ctx);
 232         } else {
 233                 worker_try_finish ();
 234         }
 235 }
 236
 237 static void
 238 init_distribute_gray_queue (void)
 239 {
 240         if (workers_distribute_gray_queue_inited) {
 241                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 242                 g_assert (workers_distribute_gray_queue.locked);
 243                 return;
 244         }
 245
 246         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 247                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 248         workers_distribute_gray_queue_inited = TRUE;
 249 }
 250
 251 void
 252 sgen_workers_init_distribute_gray_queue (void)
 253 {
 254         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent,
 255                         "Why should we init the distribute gray queue if we don't need it?");
 256         init_distribute_gray_queue ();
 257 }
 258
 259 void
 260 sgen_workers_init (int num_workers)
 261 {
 262         int i;
 263         void **workers_data_ptrs = (void **)alloca(num_workers * sizeof(void *));
 264
 265         if (!sgen_get_major_collector ()->is_concurrent) {
 266                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 267                 return;
 268         }
 269
 270         //g_print ("initing %d workers\n", num_workers);
 271
 272         workers_num = num_workers;
 273
 274         workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 275         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 276
 277         init_distribute_gray_queue ();
 278
 279         for (i = 0; i < workers_num; ++i)
 280                 workers_data_ptrs [i] = (void *) &workers_data [i];
 281
 282         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 283
 284         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 285 }
 286
 287 void
 288 sgen_workers_stop_all_workers (void)
 289 {
 290         forced_stop = TRUE;
 291
 292         sgen_thread_pool_wait_for_all_jobs ();
 293         sgen_thread_pool_idle_wait ();
 294         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 295 }
 296
 297 void
 298 sgen_workers_start_all_workers (SgenObjectOperations *object_ops)
 299 {
 300         forced_stop = FALSE;
 301         idle_func_object_ops = object_ops;
 302         mono_memory_write_barrier ();
 303
 304         sgen_workers_ensure_awake ();
 305 }
 306
 307 void
 308 sgen_workers_join (void)
 309 {
 310         int i;
 311
 312         sgen_thread_pool_wait_for_all_jobs ();
 313         sgen_thread_pool_idle_wait ();
 314         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 315
 316         /* At this point all the workers have stopped. */
 317
 318         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 319         for (i = 0; i < workers_num; ++i)
 320                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 321 }
 322
 323 /*
 324  * Can only be called if the workers are stopped.
 325  * If we're stopped, there are also no pending jobs.
 326  */
 327 gboolean
 328 sgen_workers_have_idle_work (void)
 329 {
 330         int i;
 331
 332         SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
 333
 334         if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 335                 return TRUE;
 336
 337         for (i = 0; i < workers_num; ++i) {
 338                 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
 339                         return TRUE;
 340         }
 341
 342         return FALSE;
 343 }
 344
 345 gboolean
 346 sgen_workers_all_done (void)
 347 {
 348         return workers_state == STATE_NOT_WORKING;
 349 }
 350
 351 /* Must only be used for debugging */
 352 gboolean
 353 sgen_workers_are_working (void)
 354 {
 355         return state_is_working_or_enqueued (workers_state);
 356 }
 357
 358 SgenSectionGrayQueue*
 359 sgen_workers_get_distribute_section_gray_queue (void)
 360 {
 361         return &workers_distribute_gray_queue;
 362 }
 363
 364 #endif