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
 128 void
 129 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
 130 {
 131         if (!enqueue) {
 132                 job->func (NULL, job);
 133                 sgen_thread_pool_job_free (job);
 134                 return;
 135         }
 136
 137         sgen_thread_pool_job_enqueue (job);
 138 }
 139
 140 void
 141 sgen_workers_wait_for_jobs_finished (void)
 142 {
 143         sgen_thread_pool_wait_for_all_jobs ();
 144         /*
 145          * If the idle task was never triggered or it finished before the last job did and
 146          * then didn't get triggered again, we might end up in the situation of having
 147          * something in the gray queue yet the idle task not working.  The easiest way to
 148          * make sure this doesn't stay that way is to just trigger it again after all jobs
 149          * have finished.
 150          */
 151         sgen_workers_ensure_awake ();
 152 }
 153
 154 static gboolean
 155 workers_get_work (WorkerData *data)
 156 {
 157         SgenMajorCollector *major;
 158
 159         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 160
 161         /* If we're concurrent, steal from the workers distribute gray queue. */
 162         major = sgen_get_major_collector ();
 163         if (major->is_concurrent) {
 164                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 165                 if (section) {
 166                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 167                         return TRUE;
 168                 }
 169         }
 170
 171         /* Nobody to steal from */
 172         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 173         return FALSE;
 174 }
 175
 176 static void
 177 concurrent_enqueue_check (GCObject *obj)
 178 {
 179         g_assert (sgen_concurrent_collection_in_progress ());
 180         g_assert (!sgen_ptr_in_nursery (obj));
 181         g_assert (SGEN_LOAD_VTABLE (obj));
 182 }
 183
 184 static void
 185 init_private_gray_queue (WorkerData *data)
 186 {
 187         sgen_gray_object_queue_init (&data->private_gray_queue,
 188                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 189 }
 190
 191 static void
 192 thread_pool_init_func (void *data_untyped)
 193 {
 194         WorkerData *data = data_untyped;
 195         SgenMajorCollector *major = sgen_get_major_collector ();
 196
 197         sgen_client_thread_register_worker ();
 198
 199         if (!major->is_concurrent)
 200                 return;
 201
 202         init_private_gray_queue (data);
 203 }
 204
 205 static gboolean
 206 continue_idle_func (void)
 207 {
 208         return state_is_working_or_enqueued (workers_state);
 209 }
 210
 211 static void
 212 marker_idle_func (void *data_untyped)
 213 {
 214         WorkerData *data = data_untyped;
 215
 216         SGEN_ASSERT (0, continue_idle_func (), "Why are we called when we're not supposed to work?");
 217         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 218
 219         if (workers_state == STATE_WORK_ENQUEUED) {
 220                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 221                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 222         }
 223
 224         if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data))) {
 225                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 226
 227                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 228
 229                 sgen_drain_gray_stack (ctx);
 230         } else {
 231                 worker_try_finish ();
 232         }
 233 }
 234
 235 static void
 236 init_distribute_gray_queue (void)
 237 {
 238         if (workers_distribute_gray_queue_inited) {
 239                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 240                 g_assert (workers_distribute_gray_queue.locked);
 241                 return;
 242         }
 243
 244         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 245                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 246         workers_distribute_gray_queue_inited = TRUE;
 247 }
 248
 249 void
 250 sgen_workers_init_distribute_gray_queue (void)
 251 {
 252         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent,
 253                         "Why should we init the distribute gray queue if we don't need it?");
 254         init_distribute_gray_queue ();
 255 }
 256
 257 void
 258 sgen_workers_init (int num_workers)
 259 {
 260         int i;
 261         void **workers_data_ptrs = alloca(num_workers * sizeof(void *));
 262
 263         if (!sgen_get_major_collector ()->is_concurrent) {
 264                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 265                 return;
 266         }
 267
 268         //g_print ("initing %d workers\n", num_workers);
 269
 270         workers_num = num_workers;
 271
 272         workers_data = sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 273         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 274
 275         init_distribute_gray_queue ();
 276
 277         for (i = 0; i < workers_num; ++i)
 278                 workers_data_ptrs [i] = (void *) &workers_data [i];
 279
 280         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 281
 282         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 283 }
 284
 285 void
 286 sgen_workers_stop_all_workers (void)
 287 {
 288         forced_stop = TRUE;
 289
 290         sgen_thread_pool_wait_for_all_jobs ();
 291         sgen_thread_pool_idle_wait ();
 292         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 293 }
 294
 295 void
 296 sgen_workers_start_all_workers (SgenObjectOperations *object_ops)
 297 {
 298         forced_stop = FALSE;
 299         idle_func_object_ops = object_ops;
 300         mono_memory_write_barrier ();
 301
 302         sgen_workers_ensure_awake ();
 303 }
 304
 305 void
 306 sgen_workers_join (void)
 307 {
 308         int i;
 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 /*
 322  * Can only be called if the workers are stopped.
 323  * If we're stopped, there are also no pending jobs.
 324  */
 325 gboolean
 326 sgen_workers_have_idle_work (void)
 327 {
 328         int i;
 329
 330         SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
 331
 332         if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 333                 return TRUE;
 334
 335         for (i = 0; i < workers_num; ++i) {
 336                 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
 337                         return TRUE;
 338         }
 339
 340         return FALSE;
 341 }
 342
 343 gboolean
 344 sgen_workers_all_done (void)
 345 {
 346         return workers_state == STATE_NOT_WORKING;
 347 }
 348
 349 /* Must only be used for debugging */
 350 gboolean
 351 sgen_workers_are_working (void)
 352 {
 353         return state_is_working_or_enqueued (workers_state);
 354 }
 355
 356 SgenSectionGrayQueue*
 357 sgen_workers_get_distribute_section_gray_queue (void)
 358 {
 359         return &workers_distribute_gray_queue;
 360 }
 361
 362 #endif