mono/metadata/sgen-stw.c

   1 /**
   2  * \file
   3  * Stop the world functionality
   4  *
   5  * Author:
   6  *      Paolo Molaro (lupus@ximian.com)
   7  *  Rodrigo Kumpera (kumpera@gmail.com)
   8  *
   9  * Copyright 2005-2011 Novell, Inc (http://www.novell.com)
  10  * Copyright 2011 Xamarin Inc (http://www.xamarin.com)
  11  * Copyright 2011 Xamarin, Inc.
  12  * Copyright (C) 2012 Xamarin Inc
  13  *
  14  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  15  */
  16
  17 #include "config.h"
  18 #ifdef HAVE_SGEN_GC
  19
  20 #include "sgen/sgen-gc.h"
  21 #include "sgen/sgen-protocol.h"
  22 #include "sgen/sgen-memory-governor.h"
  23 #include "sgen/sgen-workers.h"
  24 #include "metadata/profiler-private.h"
  25 #include "sgen/sgen-client.h"
  26 #include "metadata/sgen-bridge-internals.h"
  27 #include "metadata/gc-internals.h"
  28 #include "utils/mono-threads.h"
  29 #include "utils/mono-threads-debug.h"
  30
  31 #define TV_DECLARE SGEN_TV_DECLARE
  32 #define TV_GETTIME SGEN_TV_GETTIME
  33 #define TV_ELAPSED SGEN_TV_ELAPSED
  34
  35 static void sgen_unified_suspend_restart_world (void);
  36 static void sgen_unified_suspend_stop_world (void);
  37
  38 static TV_DECLARE (end_of_last_stw);
  39
  40 guint64 mono_time_since_last_stw ()
  41 {
  42         if (end_of_last_stw == 0)
  43                 return 0;
  44
  45         TV_DECLARE (current_time);
  46         TV_GETTIME (current_time);
  47         return TV_ELAPSED (end_of_last_stw, current_time);
  48 }
  49
  50 unsigned int sgen_global_stop_count = 0;
  51
  52 inline static void*
  53 align_pointer (void *ptr)
  54 {
  55         mword p = (mword)ptr;
  56         p += sizeof (gpointer) - 1;
  57         p &= ~ (sizeof (gpointer) - 1);
  58         return (void*)p;
  59 }
  60
  61 static void
  62 update_current_thread_stack (void *start)
  63 {
  64         int stack_guard = 0;
  65         SgenThreadInfo *info = mono_thread_info_current ();
  66
  67         info->client_info.stack_start = align_pointer (&stack_guard);
  68         g_assert (info->client_info.stack_start);
  69         g_assert (info->client_info.stack_start >= info->client_info.info.stack_start_limit && info->client_info.stack_start < info->client_info.info.stack_end);
  70
  71 #if !defined(MONO_CROSS_COMPILE) && MONO_ARCH_HAS_MONO_CONTEXT
  72         MONO_CONTEXT_GET_CURRENT (info->client_info.ctx);
  73 #elif defined (HOST_WASM)
  74         //nothing
  75 #else
  76         g_error ("Sgen STW requires a working mono-context");
  77 #endif
  78
  79         if (mono_gc_get_gc_callbacks ()->thread_suspend_func)
  80                 mono_gc_get_gc_callbacks ()->thread_suspend_func (info->client_info.runtime_data, NULL, &info->client_info.ctx);
  81 }
  82
  83 static void
  84 acquire_gc_locks (void)
  85 {
  86         LOCK_INTERRUPTION;
  87         mono_thread_info_suspend_lock ();
  88 }
  89
  90 static void
  91 release_gc_locks (void)
  92 {
  93         mono_thread_info_suspend_unlock ();
  94         UNLOCK_INTERRUPTION;
  95 }
  96
  97 static TV_DECLARE (stop_world_time);
  98 static unsigned long max_stw_pause_time = 0;
  99
 100 static guint64 time_stop_world;
 101 static guint64 time_restart_world;
 102
 103 /* LOCKING: assumes the GC lock is held */
 104 void
 105 sgen_client_stop_world (int generation, gboolean serial_collection)
 106 {
 107         TV_DECLARE (end_handshake);
 108
 109         MONO_PROFILER_RAISE (gc_event, (MONO_GC_EVENT_PRE_STOP_WORLD, generation, serial_collection));
 110
 111         acquire_gc_locks ();
 112
 113         MONO_PROFILER_RAISE (gc_event, (MONO_GC_EVENT_PRE_STOP_WORLD_LOCKED, generation, serial_collection));
 114
 115         update_current_thread_stack (&generation);
 116
 117         /* We start to scan after locks are taking, this ensures we won't be interrupted. */
 118         sgen_process_togglerefs ();
 119
 120         sgen_global_stop_count++;
 121         SGEN_LOG (3, "stopping world n %d from %p %p", sgen_global_stop_count, mono_thread_info_current (), (gpointer) (gsize) mono_native_thread_id_get ());
 122         TV_GETTIME (stop_world_time);
 123
 124         sgen_unified_suspend_stop_world ();
 125
 126         SGEN_LOG (3, "world stopped");
 127
 128         MONO_PROFILER_RAISE (gc_event, (MONO_GC_EVENT_POST_STOP_WORLD, generation, serial_collection));
 129
 130         TV_GETTIME (end_handshake);
 131
 132         unsigned long stop_world_tv_elapsed = TV_ELAPSED (stop_world_time, end_handshake);
 133         SGEN_LOG (2, "stopping world (time: %d usec)", (int)stop_world_tv_elapsed / 10);
 134         time_stop_world += stop_world_tv_elapsed;
 135
 136         sgen_memgov_collection_start (generation);
 137         if (sgen_need_bridge_processing ())
 138                 sgen_bridge_reset_data ();
 139 }
 140
 141 /* LOCKING: assumes the GC lock is held */
 142 void
 143 sgen_client_restart_world (int generation, gboolean serial_collection, gint64 *stw_time)
 144 {
 145         TV_DECLARE (end_sw);
 146         TV_DECLARE (start_handshake);
 147
 148         /* notify the profiler of the leftovers */
 149         /* FIXME this is the wrong spot at we can STW for non collection reasons. */
 150         if (MONO_PROFILER_ENABLED (gc_moves))
 151                 mono_sgen_gc_event_moves ();
 152
 153         if (MONO_PROFILER_ENABLED (gc_resize))
 154                 mono_sgen_gc_event_resize ();
 155
 156         MONO_PROFILER_RAISE (gc_event, (MONO_GC_EVENT_PRE_START_WORLD, generation, serial_collection));
 157
 158         FOREACH_THREAD_ALL (info) {
 159                 info->client_info.stack_start = NULL;
 160                 memset (&info->client_info.ctx, 0, sizeof (MonoContext));
 161         } FOREACH_THREAD_END
 162
 163         TV_GETTIME (start_handshake);
 164
 165         sgen_unified_suspend_restart_world ();
 166
 167         TV_GETTIME (end_sw);
 168
 169         unsigned long restart_world_tv_elapsed = TV_ELAPSED (start_handshake, end_sw);
 170         SGEN_LOG (2, "restarting world (time: %d usec)", (int)restart_world_tv_elapsed / 10);
 171         time_restart_world += restart_world_tv_elapsed;
 172
 173         unsigned long stw_pause_time = TV_ELAPSED (stop_world_time, end_sw);
 174         max_stw_pause_time = MAX (stw_pause_time, max_stw_pause_time);
 175         end_of_last_stw = end_sw;
 176
 177         SGEN_LOG (1, "restarted (pause time: %d usec, max: %d usec)", (int)stw_pause_time / 10, (int)max_stw_pause_time / 10);
 178
 179         MONO_PROFILER_RAISE (gc_event, (MONO_GC_EVENT_POST_START_WORLD, generation, serial_collection));
 180
 181         /*
 182          * We must release the thread info suspend lock after doing
 183          * the thread handshake.  Otherwise, if the GC stops the world
 184          * and a thread is in the process of starting up, but has not
 185          * yet registered (it's not in the thread_list), it is
 186          * possible that the thread does register while the world is
 187          * stopped.  When restarting the GC will then try to restart
 188          * said thread, but since it never got the suspend signal, it
 189          * cannot answer the restart signal, so a deadlock results.
 190          */
 191         release_gc_locks ();
 192
 193         MONO_PROFILER_RAISE (gc_event, (MONO_GC_EVENT_POST_START_WORLD_UNLOCKED, generation, serial_collection));
 194
 195         *stw_time = stw_pause_time;
 196 }
 197
 198 void
 199 mono_sgen_init_stw (void)
 200 {
 201         mono_counters_register ("World stop", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &time_stop_world);
 202         mono_counters_register ("World restart", MONO_COUNTER_GC | MONO_COUNTER_ULONG | MONO_COUNTER_TIME, &time_restart_world);
 203 }
 204
 205 /* Unified suspend code */
 206
 207 static gboolean
 208 sgen_is_thread_in_current_stw (SgenThreadInfo *info, int *reason)
 209 {
 210         /*
 211          * No need to check MONO_THREAD_INFO_FLAGS_NO_GC here as we rely on the
 212          * FOREACH_THREAD_EXCLUDE macro to skip such threads for us.
 213          */
 214
 215         /*
 216         We have detected that this thread is failing/dying, ignore it.
 217         FIXME: can't we merge this with thread_is_dying?
 218         */
 219         if (info->client_info.skip) {
 220                 if (reason)
 221                         *reason = 2;
 222                 return FALSE;
 223         }
 224
 225         /*
 226         Suspending the current thread will deadlock us, bad idea.
 227         */
 228         if (info == mono_thread_info_current ()) {
 229                 if (reason)
 230                         *reason = 3;
 231                 return FALSE;
 232         }
 233
 234         /*
 235         We can't suspend the workers that will do all the heavy lifting.
 236         FIXME Use some state bit in SgenThreadInfo for this.
 237         */
 238         if (sgen_thread_pool_is_thread_pool_thread (mono_thread_info_get_tid (info))) {
 239                 if (reason)
 240                         *reason = 4;
 241                 return FALSE;
 242         }
 243
 244         /*
 245         The thread has signaled that it started to detach, ignore it.
 246         FIXME: can't we merge this with skip
 247         */
 248         if (!mono_thread_info_is_live (info)) {
 249                 if (reason)
 250                         *reason = 5;
 251                 return FALSE;
 252         }
 253
 254         return TRUE;
 255 }
 256
 257 static void
 258 sgen_unified_suspend_stop_world (void)
 259 {
 260         int sleep_duration = -1;
 261
 262         // we can't lead STW if we promised not to safepoint.
 263         g_assert (!mono_thread_info_will_not_safepoint (mono_thread_info_current ()));
 264
 265         mono_threads_begin_global_suspend ();
 266         THREADS_STW_DEBUG ("[GC-STW-BEGIN][%p] *** BEGIN SUSPEND *** \n", mono_thread_info_get_tid (mono_thread_info_current ()));
 267
 268         for (MonoThreadSuspendPhase phase = MONO_THREAD_SUSPEND_PHASE_INITIAL; phase < MONO_THREAD_SUSPEND_PHASE_COUNT; phase++) {
 269                 gboolean need_next_phase = FALSE;
 270                 FOREACH_THREAD_EXCLUDE (info, MONO_THREAD_INFO_FLAGS_NO_GC) {
 271                         /* look at every thread in the first phase. */
 272                         if (phase == MONO_THREAD_SUSPEND_PHASE_INITIAL) {
 273                                 info->client_info.skip = FALSE;
 274                                 info->client_info.suspend_done = FALSE;
 275                         } else {
 276                                 /* skip threads suspended by previous phase. */
 277                                 /* threads with info->client_info->skip set to TRUE will be skipped by sgen_is_thread_in_current_stw. */
 278                                 if (info->client_info.suspend_done)
 279                                         continue;
 280                         }
 281
 282                         int reason;
 283                         if (!sgen_is_thread_in_current_stw (info, &reason)) {
 284                                 THREADS_STW_DEBUG ("[GC-STW-BEGIN-SUSPEND-%d] IGNORE thread %p skip %s reason %d\n", (int)phase, mono_thread_info_get_tid (info), info->client_info.skip ? "true" : "false", reason);
 285                                 continue;
 286                         }
 287
 288                         switch (mono_thread_info_begin_suspend (info, phase)) {
 289                         case MONO_THREAD_BEGIN_SUSPEND_SUSPENDED:
 290                                 info->client_info.skip = FALSE;
 291                                 break;
 292                         case MONO_THREAD_BEGIN_SUSPEND_SKIP:
 293                                 info->client_info.skip = TRUE;
 294                                 break;
 295                         case MONO_THREAD_BEGIN_SUSPEND_NEXT_PHASE:
 296                                 need_next_phase = TRUE;
 297                                 break;
 298                         default:
 299                                 g_assert_not_reached ();
 300                         }
 301
 302                         THREADS_STW_DEBUG ("[GC-STW-BEGIN-SUSPEND-%d] SUSPEND thread %p skip %s\n", (int)phase, mono_thread_info_get_tid (info), info->client_info.skip ? "true" : "false");
 303                 } FOREACH_THREAD_END;
 304
 305                 mono_thread_info_current ()->client_info.suspend_done = TRUE;
 306                 mono_threads_wait_pending_operations ();
 307
 308                 if (!need_next_phase)
 309                         break;
 310         }
 311
 312         for (;;) {
 313                 gint restart_counter = 0;
 314
 315                 FOREACH_THREAD_EXCLUDE (info, MONO_THREAD_INFO_FLAGS_NO_GC) {
 316                         gint suspend_count;
 317
 318                         int reason = 0;
 319                         if (info->client_info.suspend_done || !sgen_is_thread_in_current_stw (info, &reason)) {
 320                                 THREADS_STW_DEBUG ("[GC-STW-RESTART] IGNORE RESUME thread %p not been processed done %d current %d reason %d\n", mono_thread_info_get_tid (info), info->client_info.suspend_done, !sgen_is_thread_in_current_stw (info, NULL), reason);
 321                                 continue;
 322                         }
 323
 324                         /*
 325                         All threads that reach here are pristine suspended. This means the following:
 326
 327                         - We haven't accepted the previous suspend as good.
 328                         - We haven't gave up on it for this STW (it's either bad or asked not to)
 329                         */
 330                         if (!mono_thread_info_in_critical_location (info)) {
 331                                 info->client_info.suspend_done = TRUE;
 332
 333                                 THREADS_STW_DEBUG ("[GC-STW-RESTART] DONE thread %p deemed fully suspended\n", mono_thread_info_get_tid (info));
 334                                 continue;
 335                         }
 336
 337                         suspend_count = mono_thread_info_suspend_count (info);
 338                         if (!(suspend_count == 1))
 339                                 g_error ("[%p] suspend_count = %d, but should be 1", mono_thread_info_get_tid (info), suspend_count);
 340
 341                         info->client_info.skip = !mono_thread_info_begin_pulse_resume_and_request_suspension (info);
 342                         if (!info->client_info.skip)
 343                                 restart_counter += 1;
 344
 345                         THREADS_STW_DEBUG ("[GC-STW-RESTART] RESTART thread %p skip %s\n", mono_thread_info_get_tid (info), info->client_info.skip ? "true" : "false");
 346                 } FOREACH_THREAD_END
 347
 348                 mono_threads_wait_pending_operations ();
 349
 350                 if (restart_counter == 0)
 351                         break;
 352
 353                 if (sleep_duration < 0) {
 354                         mono_thread_info_yield ();
 355                         sleep_duration = 0;
 356                 } else {
 357                         g_usleep (sleep_duration);
 358                         sleep_duration += 10;
 359                 }
 360
 361                 FOREACH_THREAD_EXCLUDE (info, MONO_THREAD_INFO_FLAGS_NO_GC) {
 362                         int reason = 0;
 363                         if (info->client_info.suspend_done || !sgen_is_thread_in_current_stw (info, &reason)) {
 364                                 THREADS_STW_DEBUG ("[GC-STW-RESTART] IGNORE SUSPEND thread %p not been processed done %d current %d reason %d\n", mono_thread_info_get_tid (info), info->client_info.suspend_done, !sgen_is_thread_in_current_stw (info, NULL), reason);
 365                                 continue;
 366                         }
 367
 368                         if (!mono_thread_info_is_running (info)) {
 369                                 THREADS_STW_DEBUG ("[GC-STW-RESTART] IGNORE SUSPEND thread %p not running\n", mono_thread_info_get_tid (info));
 370                                 continue;
 371                         }
 372
 373                         switch (mono_thread_info_begin_suspend (info, MONO_THREAD_SUSPEND_PHASE_MOPUP)) {
 374                         case MONO_THREAD_BEGIN_SUSPEND_SUSPENDED:
 375                                 info->client_info.skip = FALSE;
 376                                 break;
 377                         case MONO_THREAD_BEGIN_SUSPEND_SKIP:
 378                                 info->client_info.skip = TRUE;
 379                                 break;
 380                         case MONO_THREAD_BEGIN_SUSPEND_NEXT_PHASE:
 381                                 g_assert_not_reached ();
 382                         default:
 383                                 g_assert_not_reached ();
 384                         }
 385
 386                         THREADS_STW_DEBUG ("[GC-STW-RESTART] SUSPEND thread %p skip %s\n", mono_thread_info_get_tid (info), info->client_info.skip ? "true" : "false");
 387                 } FOREACH_THREAD_END
 388
 389                 mono_threads_wait_pending_operations ();
 390         }
 391
 392         FOREACH_THREAD_EXCLUDE (info, MONO_THREAD_INFO_FLAGS_NO_GC) {
 393                 gpointer stopped_ip;
 394
 395                 int reason = 0;
 396                 if (!sgen_is_thread_in_current_stw (info, &reason)) {
 397                         g_assert (!info->client_info.suspend_done || info == mono_thread_info_current ());
 398
 399                         THREADS_STW_DEBUG ("[GC-STW-SUSPEND-END] thread %p is NOT suspended, reason %d\n", mono_thread_info_get_tid (info), reason);
 400                         continue;
 401                 }
 402
 403                 g_assert (info->client_info.suspend_done);
 404
 405                 info->client_info.ctx = mono_thread_info_get_suspend_state (info)->ctx;
 406
 407                 /* Once we remove the old suspend code, we should move sgen to directly access the state in MonoThread */
 408                 info->client_info.stack_start = (gpointer) ((char*)MONO_CONTEXT_GET_SP (&info->client_info.ctx) - REDZONE_SIZE);
 409
 410                 if (info->client_info.stack_start < info->client_info.info.stack_start_limit
 411                          || info->client_info.stack_start >= info->client_info.info.stack_end) {
 412                         /*
 413                          * Thread context is in unhandled state, most likely because it is
 414                          * dying. We don't scan it.
 415                          * FIXME We should probably rework and check the valid flag instead.
 416                          */
 417                         info->client_info.stack_start = NULL;
 418                 }
 419
 420                 stopped_ip = (gpointer) (MONO_CONTEXT_GET_IP (&info->client_info.ctx));
 421
 422                 sgen_binary_protocol_thread_suspend ((gpointer) mono_thread_info_get_tid (info), stopped_ip);
 423
 424                 THREADS_STW_DEBUG ("[GC-STW-SUSPEND-END] thread %p is suspended, stopped_ip = %p, stack = %p -> %p\n",
 425                         mono_thread_info_get_tid (info), stopped_ip, info->client_info.stack_start, info->client_info.stack_start ? info->client_info.info.stack_end : NULL);
 426         } FOREACH_THREAD_END
 427 }
 428
 429 static void
 430 sgen_unified_suspend_restart_world (void)
 431 {
 432         THREADS_STW_DEBUG ("[GC-STW-END] *** BEGIN RESUME ***\n");
 433         FOREACH_THREAD_EXCLUDE (info, MONO_THREAD_INFO_FLAGS_NO_GC) {
 434                 int reason = 0;
 435                 if (sgen_is_thread_in_current_stw (info, &reason)) {
 436                         g_assert (mono_thread_info_begin_resume (info));
 437                         THREADS_STW_DEBUG ("[GC-STW-RESUME-WORLD] RESUME thread %p\n", mono_thread_info_get_tid (info));
 438
 439                         sgen_binary_protocol_thread_restart ((gpointer) mono_thread_info_get_tid (info));
 440                 } else {
 441                         THREADS_STW_DEBUG ("[GC-STW-RESUME-WORLD] IGNORE thread %p, reason %d\n", mono_thread_info_get_tid (info), reason);
 442                 }
 443         } FOREACH_THREAD_END
 444
 445         mono_threads_wait_pending_operations ();
 446         mono_threads_end_global_suspend ();
 447 }
 448 #endif