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  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
   9  */
  10
  11 #include "config.h"
  12 #ifdef HAVE_SGEN_GC
  13
  14 #include <string.h>
  15
  16 #include "mono/sgen/sgen-gc.h"
  17 #include "mono/sgen/sgen-workers.h"
  18 #include "mono/sgen/sgen-thread-pool.h"
  19 #include "mono/utils/mono-membar.h"
  20 #include "mono/sgen/sgen-client.h"
  21
  22 static int workers_num;
  23 static volatile gboolean forced_stop;
  24 static WorkerData *workers_data;
  25
  26 static SgenSectionGrayQueue workers_distribute_gray_queue;
  27 static gboolean workers_distribute_gray_queue_inited;
  28
  29 /*
  30  * Allowed transitions:
  31  *
  32  * | from \ to          | NOT WORKING | WORKING | WORK ENQUEUED |
  33  * |--------------------+-------------+---------+---------------+
  34  * | NOT WORKING        | -           | -       | main          |
  35  * | WORKING            | worker      | -       | main          |
  36  * | WORK ENQUEUED      | -           | worker  | -             |
  37  *
  38  * The WORK ENQUEUED state guarantees that the worker thread will inspect the queue again at
  39  * least once.  Only after looking at the queue will it go back to WORKING, and then,
  40  * eventually, to NOT WORKING.  After enqueuing work the main thread transitions the state
  41  * to WORK ENQUEUED.  Signalling the worker thread to wake up is only necessary if the old
  42  * state was NOT WORKING.
  43  */
  44
  45 enum {
  46         STATE_NOT_WORKING,
  47         STATE_WORKING,
  48         STATE_WORK_ENQUEUED
  49 };
  50
  51 typedef gint32 State;
  52
  53 static volatile State workers_state;
  54
  55 static SgenObjectOperations * volatile idle_func_object_ops;
  56 static SgenThreadPoolJob * volatile preclean_job;
  57
  58 static guint64 stat_workers_num_finished;
  59
  60 static gboolean
  61 set_state (State old_state, State new_state)
  62 {
  63         SGEN_ASSERT (0, old_state != new_state, "Why are we transitioning to the same state?");
  64         if (new_state == STATE_NOT_WORKING)
  65                 SGEN_ASSERT (0, old_state == STATE_WORKING, "We can only transition to NOT WORKING from WORKING");
  66         else if (new_state == STATE_WORKING)
  67                 SGEN_ASSERT (0, old_state == STATE_WORK_ENQUEUED, "We can only transition to WORKING from WORK ENQUEUED");
  68         if (new_state == STATE_NOT_WORKING || new_state == STATE_WORKING)
  69                 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");
  70
  71         return InterlockedCompareExchange (&workers_state, new_state, old_state) == old_state;
  72 }
  73
  74 static gboolean
  75 state_is_working_or_enqueued (State state)
  76 {
  77         return state == STATE_WORKING || state == STATE_WORK_ENQUEUED;
  78 }
  79
  80 void
  81 sgen_workers_ensure_awake (void)
  82 {
  83         State old_state;
  84         gboolean did_set_state;
  85
  86         do {
  87                 old_state = workers_state;
  88
  89                 if (old_state == STATE_WORK_ENQUEUED)
  90                         break;
  91
  92                 did_set_state = set_state (old_state, STATE_WORK_ENQUEUED);
  93         } while (!did_set_state);
  94
  95         if (!state_is_working_or_enqueued (old_state))
  96                 sgen_thread_pool_idle_signal ();
  97 }
  98
  99 static void
 100 worker_try_finish (void)
 101 {
 102         State old_state;
 103
 104         ++stat_workers_num_finished;
 105
 106         do {
 107                 old_state = workers_state;
 108
 109                 SGEN_ASSERT (0, old_state != STATE_NOT_WORKING, "How did we get from doing idle work to NOT WORKING without setting it ourselves?");
 110                 if (old_state == STATE_WORK_ENQUEUED)
 111                         return;
 112                 SGEN_ASSERT (0, old_state == STATE_WORKING, "What other possibility is there?");
 113
 114                 /* We are the last thread to go to sleep. */
 115         } while (!set_state (old_state, STATE_NOT_WORKING));
 116
 117         binary_protocol_worker_finish (sgen_timestamp (), forced_stop);
 118 }
 119
 120 void
 121 sgen_workers_enqueue_job (SgenThreadPoolJob *job, gboolean enqueue)
 122 {
 123         if (!enqueue) {
 124                 job->func (NULL, job);
 125                 sgen_thread_pool_job_free (job);
 126                 return;
 127         }
 128
 129         sgen_thread_pool_job_enqueue (job);
 130 }
 131
 132 void
 133 sgen_workers_wait_for_jobs_finished (void)
 134 {
 135         sgen_thread_pool_wait_for_all_jobs ();
 136         /*
 137          * If the idle task was never triggered or it finished before the last job did and
 138          * then didn't get triggered again, we might end up in the situation of having
 139          * something in the gray queue yet the idle task not working.  The easiest way to
 140          * make sure this doesn't stay that way is to just trigger it again after all jobs
 141          * have finished.
 142          */
 143         sgen_workers_ensure_awake ();
 144 }
 145
 146 static gboolean
 147 workers_get_work (WorkerData *data)
 148 {
 149         SgenMajorCollector *major;
 150
 151         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 152
 153         /* If we're concurrent, steal from the workers distribute gray queue. */
 154         major = sgen_get_major_collector ();
 155         if (major->is_concurrent) {
 156                 GrayQueueSection *section = sgen_section_gray_queue_dequeue (&workers_distribute_gray_queue);
 157                 if (section) {
 158                         sgen_gray_object_enqueue_section (&data->private_gray_queue, section);
 159                         return TRUE;
 160                 }
 161         }
 162
 163         /* Nobody to steal from */
 164         g_assert (sgen_gray_object_queue_is_empty (&data->private_gray_queue));
 165         return FALSE;
 166 }
 167
 168 static void
 169 concurrent_enqueue_check (GCObject *obj)
 170 {
 171         g_assert (sgen_concurrent_collection_in_progress ());
 172         g_assert (!sgen_ptr_in_nursery (obj));
 173         g_assert (SGEN_LOAD_VTABLE (obj));
 174 }
 175
 176 static void
 177 init_private_gray_queue (WorkerData *data)
 178 {
 179         sgen_gray_object_queue_init (&data->private_gray_queue,
 180                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 181 }
 182
 183 static void
 184 thread_pool_init_func (void *data_untyped)
 185 {
 186         WorkerData *data = (WorkerData *)data_untyped;
 187         SgenMajorCollector *major = sgen_get_major_collector ();
 188
 189         sgen_client_thread_register_worker ();
 190
 191         if (!major->is_concurrent)
 192                 return;
 193
 194         init_private_gray_queue (data);
 195 }
 196
 197 static gboolean
 198 continue_idle_func (void)
 199 {
 200         return state_is_working_or_enqueued (workers_state);
 201 }
 202
 203 static void
 204 marker_idle_func (void *data_untyped)
 205 {
 206         WorkerData *data = (WorkerData *)data_untyped;
 207
 208         SGEN_ASSERT (0, continue_idle_func (), "Why are we called when we're not supposed to work?");
 209         SGEN_ASSERT (0, sgen_concurrent_collection_in_progress (), "The worker should only mark in concurrent collections.");
 210
 211         if (workers_state == STATE_WORK_ENQUEUED) {
 212                 set_state (STATE_WORK_ENQUEUED, STATE_WORKING);
 213                 SGEN_ASSERT (0, workers_state != STATE_NOT_WORKING, "How did we get from WORK ENQUEUED to NOT WORKING?");
 214         }
 215
 216         if (!forced_stop && (!sgen_gray_object_queue_is_empty (&data->private_gray_queue) || workers_get_work (data))) {
 217                 ScanCopyContext ctx = CONTEXT_FROM_OBJECT_OPERATIONS (idle_func_object_ops, &data->private_gray_queue);
 218
 219                 SGEN_ASSERT (0, !sgen_gray_object_queue_is_empty (&data->private_gray_queue), "How is our gray queue empty if we just got work?");
 220
 221                 sgen_drain_gray_stack (ctx);
 222         } else {
 223                 SgenThreadPoolJob *job = preclean_job;
 224                 if (job) {
 225                         sgen_thread_pool_job_enqueue (job);
 226                         preclean_job = NULL;
 227                 } else {
 228                         worker_try_finish ();
 229                 }
 230         }
 231 }
 232
 233 static void
 234 init_distribute_gray_queue (void)
 235 {
 236         if (workers_distribute_gray_queue_inited) {
 237                 g_assert (sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue));
 238                 g_assert (workers_distribute_gray_queue.locked);
 239                 return;
 240         }
 241
 242         sgen_section_gray_queue_init (&workers_distribute_gray_queue, TRUE,
 243                         sgen_get_major_collector ()->is_concurrent ? concurrent_enqueue_check : NULL);
 244         workers_distribute_gray_queue_inited = TRUE;
 245 }
 246
 247 void
 248 sgen_workers_init_distribute_gray_queue (void)
 249 {
 250         SGEN_ASSERT (0, sgen_get_major_collector ()->is_concurrent,
 251                         "Why should we init the distribute gray queue if we don't need it?");
 252         init_distribute_gray_queue ();
 253 }
 254
 255 void
 256 sgen_workers_init (int num_workers)
 257 {
 258         int i;
 259         void **workers_data_ptrs = (void **)alloca(num_workers * sizeof(void *));
 260
 261         if (!sgen_get_major_collector ()->is_concurrent) {
 262                 sgen_thread_pool_init (num_workers, thread_pool_init_func, NULL, NULL, NULL);
 263                 return;
 264         }
 265
 266         //g_print ("initing %d workers\n", num_workers);
 267
 268         workers_num = num_workers;
 269
 270         workers_data = (WorkerData *)sgen_alloc_internal_dynamic (sizeof (WorkerData) * num_workers, INTERNAL_MEM_WORKER_DATA, TRUE);
 271         memset (workers_data, 0, sizeof (WorkerData) * num_workers);
 272
 273         init_distribute_gray_queue ();
 274
 275         for (i = 0; i < workers_num; ++i)
 276                 workers_data_ptrs [i] = (void *) &workers_data [i];
 277
 278         sgen_thread_pool_init (num_workers, thread_pool_init_func, marker_idle_func, continue_idle_func, workers_data_ptrs);
 279
 280         mono_counters_register ("# workers finished", MONO_COUNTER_GC | MONO_COUNTER_ULONG, &stat_workers_num_finished);
 281 }
 282
 283 void
 284 sgen_workers_stop_all_workers (void)
 285 {
 286         preclean_job = NULL;
 287         mono_memory_write_barrier ();
 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, SgenThreadPoolJob *job)
 297 {
 298         forced_stop = FALSE;
 299         idle_func_object_ops = object_ops;
 300         preclean_job = job;
 301         mono_memory_write_barrier ();
 302
 303         sgen_workers_ensure_awake ();
 304 }
 305
 306 void
 307 sgen_workers_join (void)
 308 {
 309         int i;
 310
 311         sgen_thread_pool_wait_for_all_jobs ();
 312         sgen_thread_pool_idle_wait ();
 313         SGEN_ASSERT (0, workers_state == STATE_NOT_WORKING, "Can only signal enqueue work when in no work state");
 314
 315         /* At this point all the workers have stopped. */
 316
 317         SGEN_ASSERT (0, sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue), "Why is there still work left to do?");
 318         for (i = 0; i < workers_num; ++i)
 319                 SGEN_ASSERT (0, sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue), "Why is there still work left to do?");
 320 }
 321
 322 /*
 323  * Can only be called if the workers are stopped.
 324  * If we're stopped, there are also no pending jobs.
 325  */
 326 gboolean
 327 sgen_workers_have_idle_work (void)
 328 {
 329         int i;
 330
 331         SGEN_ASSERT (0, forced_stop && sgen_workers_all_done (), "Checking for idle work should only happen if the workers are stopped.");
 332
 333         if (!sgen_section_gray_queue_is_empty (&workers_distribute_gray_queue))
 334                 return TRUE;
 335
 336         for (i = 0; i < workers_num; ++i) {
 337                 if (!sgen_gray_object_queue_is_empty (&workers_data [i].private_gray_queue))
 338                         return TRUE;
 339         }
 340
 341         return FALSE;
 342 }
 343
 344 gboolean
 345 sgen_workers_all_done (void)
 346 {
 347         return workers_state == STATE_NOT_WORKING;
 348 }
 349
 350 /* Must only be used for debugging */
 351 gboolean
 352 sgen_workers_are_working (void)
 353 {
 354         return state_is_working_or_enqueued (workers_state);
 355 }
 356
 357 SgenSectionGrayQueue*
 358 sgen_workers_get_distribute_section_gray_queue (void)
 359 {
 360         return &workers_distribute_gray_queue;
 361 }
 362
 363 #endif