mono/utils/mono-threads-coop.c

   1  /*
   2  * mono-threads.c: Coop threading
   3  *
   4  * Author:
   5  *      Rodrigo Kumpera (kumpera@gmail.com)
   6  *
   7  * Copyright 2015 Xamarin, Inc (http://www.xamarin.com)
   8  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
   9  */
  10
  11 #include <config.h>
  12
  13 /* enable pthread extensions */
  14 #ifdef TARGET_MACH
  15 #define _DARWIN_C_SOURCE
  16 #endif
  17
  18 #include <mono/utils/mono-compiler.h>
  19 #include <mono/utils/mono-threads.h>
  20 #include <mono/utils/mono-tls.h>
  21 #include <mono/utils/hazard-pointer.h>
  22 #include <mono/utils/mono-memory-model.h>
  23 #include <mono/utils/mono-mmap.h>
  24 #include <mono/utils/atomic.h>
  25 #include <mono/utils/mono-time.h>
  26 #include <mono/utils/mono-counters.h>
  27 #include <mono/utils/mono-threads-coop.h>
  28 #include <mono/utils/mono-threads-api.h>
  29 #include <mono/utils/checked-build.h>
  30
  31 #ifdef TARGET_OSX
  32 #include <mono/utils/mach-support.h>
  33 #endif
  34
  35 #ifdef _MSC_VER
  36 // TODO: Find MSVC replacement for __builtin_unwind_init
  37 #define SAVE_REGS_ON_STACK g_assert_not_reached ();
  38 #else
  39 #define SAVE_REGS_ON_STACK __builtin_unwind_init ();
  40 #endif
  41
  42 volatile size_t mono_polling_required;
  43
  44 // FIXME: This would be more efficient if instead of instantiating the stack it just pushed a simple depth counter up and down,
  45 // perhaps with a per-thread cookie in the high bits.
  46 #ifdef ENABLE_CHECKED_BUILD_GC
  47 // Maintains a single per-thread stack of ints, used to ensure nesting is not violated
  48 MonoNativeTlsKey coop_reset_count_stack_key;
  49 static int coop_tls_push (int v) {
  50         GArray *stack = mono_native_tls_get_value (coop_reset_count_stack_key);
  51         if (!stack) {
  52                 stack = g_array_new (FALSE,FALSE,sizeof(int));
  53                 mono_native_tls_set_value (coop_reset_count_stack_key, stack);
  54         }
  55         g_array_append_val (stack, v);
  56         return stack->len;
  57 }
  58 static int coop_tls_pop (int *v) {
  59         GArray *stack = mono_native_tls_get_value (coop_reset_count_stack_key);
  60         if (!stack || 0 == stack->len)
  61                 return -1;
  62         stack->len--;
  63         *v = g_array_index (stack, int, stack->len);
  64         int len = stack->len;
  65         if (0 == len) {
  66                 g_array_free (stack,TRUE);
  67                 mono_native_tls_set_value (coop_reset_count_stack_key, NULL);
  68         }
  69         return len;
  70 }
  71 #endif
  72
  73 static int coop_reset_blocking_count;
  74 static int coop_try_blocking_count;
  75 static int coop_do_blocking_count;
  76 static int coop_do_polling_count;
  77 static int coop_save_count;
  78
  79 void
  80 mono_threads_state_poll (void)
  81 {
  82         MonoThreadInfo *info;
  83
  84         g_assert (mono_threads_is_coop_enabled ());
  85
  86         ++coop_do_polling_count;
  87
  88         info = mono_thread_info_current_unchecked ();
  89         if (!info)
  90                 return;
  91         THREADS_SUSPEND_DEBUG ("FINISH SELF SUSPEND OF %p\n", mono_thread_info_get_tid (info));
  92
  93         /* Fast check for pending suspend requests */
  94         if (!(info->thread_state & (STATE_ASYNC_SUSPEND_REQUESTED | STATE_SELF_SUSPEND_REQUESTED)))
  95                 return;
  96
  97         ++coop_save_count;
  98         mono_threads_get_runtime_callbacks ()->thread_state_init (&info->thread_saved_state [SELF_SUSPEND_STATE_INDEX]);
  99
 100         /* commit the saved state and notify others if needed */
 101         switch (mono_threads_transition_state_poll (info)) {
 102         case SelfSuspendResumed:
 103                 return;
 104         case SelfSuspendWait:
 105                 mono_thread_info_wait_for_resume (info);
 106                 break;
 107         case SelfSuspendNotifyAndWait:
 108                 mono_threads_notify_initiator_of_suspend (info);
 109                 mono_thread_info_wait_for_resume (info);
 110                 break;
 111         }
 112 }
 113
 114 static void *
 115 return_stack_ptr ()
 116 {
 117         gpointer i;
 118         return &i;
 119 }
 120
 121 static void
 122 copy_stack_data (MonoThreadInfo *info, void* stackdata_begin)
 123 {
 124         MonoThreadUnwindState *state;
 125         int stackdata_size;
 126         void* stackdata_end = return_stack_ptr ();
 127
 128         SAVE_REGS_ON_STACK;
 129
 130         state = &info->thread_saved_state [SELF_SUSPEND_STATE_INDEX];
 131
 132         stackdata_size = (char*)stackdata_begin - (char*)stackdata_end;
 133
 134         if (((gsize) stackdata_begin & (SIZEOF_VOID_P - 1)) != 0)
 135                 g_error ("stackdata_begin (%p) must be %d-byte aligned", stackdata_begin, SIZEOF_VOID_P);
 136         if (((gsize) stackdata_end & (SIZEOF_VOID_P - 1)) != 0)
 137                 g_error ("stackdata_end (%p) must be %d-byte aligned", stackdata_end, SIZEOF_VOID_P);
 138
 139         if (stackdata_size <= 0)
 140                 g_error ("stackdata_size = %d, but must be > 0, stackdata_begin = %p, stackdata_end = %p", stackdata_size, stackdata_begin, stackdata_end);
 141
 142         g_byte_array_set_size (info->stackdata, stackdata_size);
 143         state->gc_stackdata = info->stackdata->data;
 144         memcpy (state->gc_stackdata, stackdata_end, stackdata_size);
 145
 146         state->gc_stackdata_size = stackdata_size;
 147 }
 148
 149 void*
 150 mono_threads_prepare_blocking (void* stackdata)
 151 {
 152         MonoThreadInfo *info;
 153
 154         if (!mono_threads_is_coop_enabled ())
 155                 return NULL;
 156
 157         ++coop_do_blocking_count;
 158
 159         info = mono_thread_info_current_unchecked ();
 160         /* If the thread is not attached, it doesn't make sense prepare for suspend. */
 161         if (!info || !mono_thread_info_is_live (info)) {
 162                 THREADS_SUSPEND_DEBUG ("PREPARE-BLOCKING failed %p\n", info ? mono_thread_info_get_tid (info) : NULL);
 163                 return NULL;
 164         }
 165
 166         copy_stack_data (info, stackdata);
 167
 168 retry:
 169         ++coop_save_count;
 170         mono_threads_get_runtime_callbacks ()->thread_state_init (&info->thread_saved_state [SELF_SUSPEND_STATE_INDEX]);
 171
 172         switch (mono_threads_transition_do_blocking (info)) {
 173         case DoBlockingContinue:
 174                 break;
 175         case DoBlockingPollAndRetry:
 176                 mono_threads_state_poll ();
 177                 goto retry;
 178         }
 179
 180         return info;
 181 }
 182
 183 void
 184 mono_threads_finish_blocking (void *cookie, void* stackdata)
 185 {
 186         static gboolean warned_about_bad_transition;
 187         MonoThreadInfo *info;
 188
 189         if (!mono_threads_is_coop_enabled ())
 190                 return;
 191
 192         info = (MonoThreadInfo *)cookie;
 193         if (!info)
 194                 return;
 195
 196         g_assert (info == mono_thread_info_current_unchecked ());
 197
 198         switch (mono_threads_transition_done_blocking (info)) {
 199         case DoneBlockingAborted:
 200                 if (!warned_about_bad_transition) {
 201                         warned_about_bad_transition = TRUE;
 202                         g_warning ("[%p] Blocking call ended in running state for, this might lead to unbound GC pauses.", mono_thread_info_get_tid (info));
 203                 }
 204                 mono_threads_state_poll ();
 205                 break;
 206         case DoneBlockingOk:
 207                 info->thread_saved_state [SELF_SUSPEND_STATE_INDEX].valid = FALSE;
 208                 break;
 209         case DoneBlockingWait:
 210                 THREADS_SUSPEND_DEBUG ("state polling done, notifying of resume\n");
 211                 mono_thread_info_wait_for_resume (info);
 212                 break;
 213         default:
 214                 g_error ("Unknown thread state");
 215         }
 216 }
 217
 218
 219 gpointer
 220 mono_threads_cookie_for_reset_blocking_start (MonoThreadInfo *info, int reset_blocking_count)
 221 {
 222 #ifdef ENABLE_CHECKED_BUILD_GC
 223         g_assert (reset_blocking_count != 0);
 224         if (mono_check_mode_enabled (MONO_CHECK_MODE_GC)) {
 225                 int level = coop_tls_push (reset_blocking_count);
 226                 //g_warning("Entering reset nest; level %d; cookie %d\n", level, reset_blocking_count);
 227                 return (void *)(intptr_t)reset_blocking_count;
 228         }
 229 #endif
 230
 231         return info;
 232 }
 233
 234 void*
 235 mono_threads_reset_blocking_start (void* stackdata)
 236 {
 237         MonoThreadInfo *info;
 238
 239         if (!mono_threads_is_coop_enabled ())
 240                 return NULL;
 241
 242         info = mono_thread_info_current_unchecked ();
 243
 244 #ifdef ENABLE_CHECKED_BUILD_GC
 245         int reset_blocking_count = InterlockedIncrement (&coop_reset_blocking_count);
 246         // In this mode, the blocking count is used as the reset cookie. We would prefer
 247         // (but do not require) this to be unique across invocations and threads.
 248         if (reset_blocking_count == 0) // We *do* require it be nonzero
 249                 reset_blocking_count = coop_reset_blocking_count = 1;
 250 #else
 251         int reset_blocking_count = ++coop_reset_blocking_count;
 252 #endif
 253
 254         /* If the thread is not attached, it doesn't make sense prepare for suspend. */
 255         if (!info || !mono_thread_info_is_live (info))
 256                 return NULL;
 257
 258         copy_stack_data (info, stackdata);
 259
 260         switch (mono_threads_transition_abort_blocking (info)) {
 261         case AbortBlockingIgnore:
 262                 info->thread_saved_state [SELF_SUSPEND_STATE_INDEX].valid = FALSE;
 263                 return NULL;
 264         case AbortBlockingIgnoreAndPoll:
 265                 mono_threads_state_poll ();
 266                 return NULL;
 267         case AbortBlockingOk:
 268                 info->thread_saved_state [SELF_SUSPEND_STATE_INDEX].valid = FALSE;
 269                 break;
 270         case AbortBlockingWait:
 271                 mono_thread_info_wait_for_resume (info);
 272                 break;
 273         default:
 274                 g_error ("Unknown thread state");
 275         }
 276
 277         return mono_threads_cookie_for_reset_blocking_start (info, reset_blocking_count);
 278 }
 279
 280 void
 281 mono_threads_reset_blocking_end (void *cookie, void* stackdata)
 282 {
 283         if (!mono_threads_is_coop_enabled ())
 284                 return;
 285
 286         if (!cookie)
 287                 return;
 288
 289 #ifdef ENABLE_CHECKED_BUILD_GC
 290         if (mono_check_mode_enabled (MONO_CHECK_MODE_GC)) {
 291                 int received_cookie = (int)(intptr_t)cookie;
 292                 int desired_cookie;
 293                 int level = coop_tls_pop (&desired_cookie);
 294                 //g_warning("Leaving reset nest; back to level %d; desired cookie %d; received cookie %d\n", level, desired_cookie, received_cookie);
 295                 if (level < 0)
 296                         mono_fatal_with_history ("Expected cookie %d but found no stack at all, %x\n", desired_cookie, level);
 297                 if (desired_cookie != received_cookie)
 298                         mono_fatal_with_history ("Expected cookie %d but received %d\n", desired_cookie, received_cookie);
 299         } else // Notice this matches the line after the endif
 300 #endif
 301         {
 302                 g_assert (((MonoThreadInfo *)cookie) == mono_thread_info_current_unchecked ());
 303         }
 304
 305         mono_threads_prepare_blocking (stackdata);
 306 }
 307
 308 void
 309 mono_threads_init_coop (void)
 310 {
 311         if (!mono_threads_is_coop_enabled ())
 312                 return;
 313
 314         mono_counters_register ("Coop Reset Blocking", MONO_COUNTER_GC | MONO_COUNTER_INT, &coop_reset_blocking_count);
 315         mono_counters_register ("Coop Try Blocking", MONO_COUNTER_GC | MONO_COUNTER_INT, &coop_try_blocking_count);
 316         mono_counters_register ("Coop Do Blocking", MONO_COUNTER_GC | MONO_COUNTER_INT, &coop_do_blocking_count);
 317         mono_counters_register ("Coop Do Polling", MONO_COUNTER_GC | MONO_COUNTER_INT, &coop_do_polling_count);
 318         mono_counters_register ("Coop Save Count", MONO_COUNTER_GC | MONO_COUNTER_INT, &coop_save_count);
 319         //See the above for what's wrong here.
 320
 321 #ifdef ENABLE_CHECKED_BUILD_GC
 322         mono_native_tls_alloc (&coop_reset_count_stack_key, NULL);
 323 #endif
 324 }
 325
 326 void
 327 mono_threads_coop_begin_global_suspend (void)
 328 {
 329         if (mono_threads_is_coop_enabled ())
 330                 mono_polling_required = 1;
 331 }
 332
 333 void
 334 mono_threads_coop_end_global_suspend (void)
 335 {
 336         if (mono_threads_is_coop_enabled ())
 337                 mono_polling_required = 0;
 338 }
 339
 340 gpointer
 341 mono_threads_enter_gc_unsafe_region (gpointer* stackdata)
 342 {
 343         if (!mono_threads_is_coop_enabled ())
 344                 return NULL;
 345
 346         return mono_threads_reset_blocking_start (stackdata);
 347 }
 348
 349 void
 350 mono_threads_exit_gc_unsafe_region (gpointer cookie, gpointer* stackdata)
 351 {
 352         if (!mono_threads_is_coop_enabled ())
 353                 return;
 354
 355         mono_threads_reset_blocking_end (cookie, stackdata);
 356 }
 357
 358 void
 359 mono_threads_assert_gc_unsafe_region (void)
 360 {
 361         MONO_REQ_GC_UNSAFE_MODE;
 362 }
 363
 364 gpointer
 365 mono_threads_enter_gc_safe_region (gpointer *stackdata)
 366 {
 367         if (!mono_threads_is_coop_enabled ())
 368                 return NULL;
 369
 370         return mono_threads_prepare_blocking (stackdata);
 371 }
 372
 373 void
 374 mono_threads_exit_gc_safe_region (gpointer cookie, gpointer *stackdata)
 375 {
 376         if (!mono_threads_is_coop_enabled ())
 377                 return;
 378
 379         mono_threads_finish_blocking (cookie, stackdata);
 380 }
 381
 382 void
 383 mono_threads_assert_gc_safe_region (void)
 384 {
 385         MONO_REQ_GC_SAFE_MODE;
 386 }