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 static SgenThreadPoolJob * volatile preclean_job;
  68
  69 static guint64 stat_workers_num_finished;
  70
  71 static gboolean
  72 set_state (State old_state, State new_state)
  73 {
  74         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  75         if (new_state == STATE_NOT_WORKING)
  76                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  77         else if (new_state == STATE_WORKING)
  78                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  79         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  80                 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
  82         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  83 }
  84
  85 static gboolean
  86 state_is_working_or_enqueued (State state)
  87 {
  88         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  89 }
  90
  91 void
  92 sgen_workers_ensure_awake (void)
  93 {
  94         State old_state;
  95         gboolean did_set_state;
  96
  97         do {
  98                 old_state = workers_state;
  99
 100                 if (old_state == STATE_WORK_ENQUEUED)
 101                         break;
 102
 103                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
 104         } while (!did_set_state);
 105
 106         if (!state_is_working_or_enqueued (old_state))
 107                 sgen_thread_pool_idle_signal ();
 108 }
 109
 110 static void
 111 worker_try_finish (void)
 112 {
 113         State old_state;
 114
 115         ++stat_workers_num_finished;
 116
 117         do {
 118                 old_state = workers_state;
 119
 120                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 121                 if (old_state == STATE_WORK_ENQUEUED)
 122                         return;
 123                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 124
 125                 /* We are the last thread to go to sleep. */
 126         } while (!set_state (old_state, STATE_NOT_WORKING));
 127
 128         binary_protocol_worker_finish (sgen_timestamp (), forced_stop);
 129 }
 130
 131 void
 132 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
 133 {
 134         if (!enqueue) {
 135                 job->func (NULL, job);
 136                 sgen_thread_pool_job_free (job);
 137                 return;
 138         }
 139
 140         sgen_thread_pool_job_enqueue (job);
 141 }
 142
 143 void
 144 sgen_workers_wait_for_jobs_finished (void)
 145 {
 146         sgen_thread_pool_wait_for_all_jobs ();
 147         /*
 148          * If the idle task was never triggered or it finished before the last job did and
 149          * then didn't get triggered again, we might end up in the situation of having
 150          * something in the gray queue yet the idle task not working.  The easiest way to
 151          * make sure this doesn't stay that way is to just trigger it again after all jobs
 152          * have finished.
 153          */
 154         sgen_workers_ensure_awake ();
 155 }
 156
 157 static gboolean
 158 workers_get_work (WorkerData *data)
 159 {
 160         SgenMajorCollector *major;
 161
 162         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 163
 164         /* If we're concurrent, steal from the workers distribute gray queue. */
 165         major = sgen_get_major_collector ();
 166         if (major->is_concurrent) {
 167                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 168                 if (section) {
 169                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 170                         return TRUE;
 171                 }
 172         }
 173
 174         /* Nobody to steal from */
 175         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 176         return FALSE;
 177 }
 178
 179 static void
 180 concurrent_enqueue_check (GCObject *obj)
 181 {
 182         g_assert (sgen_concurrent_collection_in_progress ());
 183         g_assert (!sgen_ptr_in_nursery (obj));
 184         g_assert (SGEN_LOAD_VTABLE (obj));
 185 }
 186
 187 static void
 188 init_private_gray_queue (WorkerData *data)
 189 {
 190         sgen_gray_object_queue_init (&data->private_gray_queue,
 191                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 192 }
 193
 194 static void
 195 thread_pool_init_func (void *data_untyped)
 196 {
 197         WorkerData *data = (WorkerData *)data_untyped;
 198         SgenMajorCollector *major = sgen_get_major_collector ();
 199
 200         sgen_client_thread_register_worker ();
 201
 202         if (!major->is_concurrent)
 203                 return;
 204
 205         init_private_gray_queue (data);
 206 }
 207
 208 static gboolean
 209 continue_idle_func (void)
 210 {
 211         return state_is_working_or_enqueued (workers_state);
 212 }
 213
 214 static void
 215 marker_idle_func (void *data_untyped)
 216 {
 217         WorkerData *data = (WorkerData *)data_untyped;
 218
 219         SGEN_ASSERT (0, continue_idle_func (), "Why are we called when we're not supposed to work?");
 220         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 221
 222         if (workers_state == STATE_WORK_ENQUEUED) {
 223                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 224                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 225         }
 226
 227         if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data))) {
 228                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 229
 230                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 231
 232                 sgen_drain_gray_stack (ctx);
 233         } else {
 234                 SgenThreadPoolJob *job = preclean_job;
 235                 if (job) {
 236                         sgen_thread_pool_job_enqueue (job);
 237                         preclean_job = NULL;
 238                 } else {
 239                         worker_try_finish ();
 240                 }
 241         }
 242 }
 243
 244 static void
 245 init_distribute_gray_queue (void)
 246 {
 247         if (workers_distribute_gray_queue_inited) {
 248                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 249                 g_assert (workers_distribute_gray_queue.locked);
 250                 return;
 251         }
 252
 253         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 254                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 255         workers_distribute_gray_queue_inited = TRUE;
 256 }
 257
 258 void
 259 sgen_workers_init_distribute_gray_queue (void)
 260 {
 261         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent,
 262                         "Why should we init the distribute gray queue if we don't need it?");
 263         init_distribute_gray_queue ();
 264 }
 265
 266 void
 267 sgen_workers_init (int num_workers)
 268 {
 269         int i;
 270         void **workers_data_ptrs = (void **)alloca(num_workers * sizeof(void *));
 271
 272         if (!sgen_get_major_collector ()->is_concurrent) {
 273                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 274                 return;
 275         }
 276
 277         //g_print ("initing %d workers\n", num_workers);
 278
 279         workers_num = num_workers;
 280
 281         workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 282         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 283
 284         init_distribute_gray_queue ();
 285
 286         for (i = 0; i < workers_num; ++i)
 287                 workers_data_ptrs [i] = (void *) &workers_data [i];
 288
 289         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 290
 291         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 292 }
 293
 294 void
 295 sgen_workers_stop_all_workers (void)
 296 {
 297         preclean_job = NULL;
 298         mono_memory_write_barrier ();
 299         forced_stop = TRUE;
 300
 301         sgen_thread_pool_wait_for_all_jobs ();
 302         sgen_thread_pool_idle_wait ();
 303         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 304 }
 305
 306 void
 307 sgen_workers_start_all_workers (SgenObjectOperations *object_ops, SgenThreadPoolJob *job)
 308 {
 309         forced_stop = FALSE;
 310         idle_func_object_ops = object_ops;
 311         preclean_job = job;
 312         mono_memory_write_barrier ();
 313
 314         sgen_workers_ensure_awake ();
 315 }
 316
 317 void
 318 sgen_workers_join (void)
 319 {
 320         int i;
 321
 322         sgen_thread_pool_wait_for_all_jobs ();
 323         sgen_thread_pool_idle_wait ();
 324         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 325
 326         /* At this point all the workers have stopped. */
 327
 328         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 329         for (i = 0; i < workers_num; ++i)
 330                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 331 }
 332
 333 /*
 334  * Can only be called if the workers are stopped.
 335  * If we're stopped, there are also no pending jobs.
 336  */
 337 gboolean
 338 sgen_workers_have_idle_work (void)
 339 {
 340         int i;
 341
 342         SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
 343
 344         if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 345                 return TRUE;
 346
 347         for (i = 0; i < workers_num; ++i) {
 348                 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
 349                         return TRUE;
 350         }
 351
 352         return FALSE;
 353 }
 354
 355 gboolean
 356 sgen_workers_all_done (void)
 357 {
 358         return workers_state == STATE_NOT_WORKING;
 359 }
 360
 361 /* Must only be used for debugging */
 362 gboolean
 363 sgen_workers_are_working (void)
 364 {
 365         return state_is_working_or_enqueued (workers_state);
 366 }
 367
 368 SgenSectionGrayQueue*
 369 sgen_workers_get_distribute_section_gray_queue (void)
 370 {
 371         return &workers_distribute_gray_queue;
 372 }
 373
 374 #endif