mono/metadata/handle.c

   1 /*
   2  * handle.c: Handle to object in native code
   3  *
   4  * Authors:
   5  *  - Ludovic Henry <ludovic@xamarin.com>
   6  *  - Aleksey Klieger <aleksey.klieger@xamarin.com>
   7  *  - Rodrigo Kumpera <kumpera@xamarin.com>
   8  *
   9  * Copyright 2016 Dot net foundation.
  10  * Licensed under the MIT license. See LICENSE file in the project root for full license information.
  11  */
  12
  13 #include <config.h>
  14 #include <glib.h>
  15
  16 #include <mono/metadata/handle.h>
  17 #include <mono/metadata/object-internals.h>
  18 #include <mono/metadata/gc-internals.h>
  19 #include <mono/utils/atomic.h>
  20 #include <mono/utils/mono-lazy-init.h>
  21 #include <mono/utils/mono-threads.h>
  22 /* TODO (missing pieces)
  23
  24 Add counters for:
  25         number of stack marks
  26         stack marks per icall
  27         mix/max/avg size of stack marks
  28         handle stack wastage
  29
  30 Actually do something in mono_handle_verify
  31
  32 Shrink the handles stack in mono_handle_stack_scan
  33 Properly report it to the profiler.
  34 Add a boehm implementation
  35
  36 TODO (things to explore):
  37
  38 There's no convenient way to wrap the object allocation function.
  39 Right now we do this:
  40         MonoCultureInfoHandle culture = MONO_HANDLE_NEW (MonoCultureInfo, mono_object_new_checked (domain, klass, &error));
  41
  42 Maybe what we need is a round of cleanup around all exposed types in the runtime to unify all helpers under the same hoof.
  43 Combine: MonoDefaults, GENERATE_GET_CLASS_WITH_CACHE, TYPED_HANDLE_DECL and friends.
  44         This would solve the age old issue of making it clear which types are optional and tell that to the linker.
  45         We could then generate neat type safe wrappers.
  46 */
  47
  48 /*
  49  * NOTE: Async suspend
  50  *
  51  * If we are running with cooperative GC, all the handle stack
  52  * manipulation will complete before a GC thread scans the handle
  53  * stack. If we are using async suspend, however, a thread may be
  54  * trying to allocate a new handle, or unwind the handle stack when
  55  * the GC stops the world.
  56  *
  57  * In particular, we need to ensure that if the mutator thread is
  58  * suspended while manipulating the handle stack, the stack is in a
  59  * good enough state to be scanned.  In particular, the size of each
  60  * chunk should be updated before an object is written into the
  61  * handle, and chunks to be scanned (between bottom and top) should
  62  * always be valid.
  63  *
  64  * Note that the handle stack is scanned PRECISELY (see
  65  * sgen_client_scan_thread_data ()).  That means there should not be
  66  * stale objects scanned.  So when we manipulate the size of a chunk,
  67  * wemust ensure that the newly scannable slot is either null or
  68  * points to a valid value.
  69  */
  70
  71 const MonoObjectHandle mono_null_value_handle = NULL;
  72
  73 #define THIS_IS_AN_OK_NUMBER_OF_HANDLES 100
  74
  75 /* Actual handles implementation */
  76 MonoRawHandle
  77 mono_handle_new (MonoObject *object)
  78 {
  79         MonoThreadInfo *info = mono_thread_info_current ();
  80         HandleStack *handles = (HandleStack *)info->handle_stack;
  81         HandleChunk *top = handles->top;
  82
  83 retry:
  84         if (G_LIKELY (top->size < OBJECTS_PER_HANDLES_CHUNK)) {
  85                 int idx = top->size;
  86                 /* can be interrupted anywhere here, so:
  87                  * 1. make sure the new slot is null
  88                  * 2. make the new slot scannable (increment size)
  89                  * 3. put a valid object in there
  90                  *
  91                  * (have to do 1 then 3 so that if we're interrupted
  92                  * between 1 and 2, the object is still live)
  93                  */
  94                 top->objects [idx] = NULL;
  95                 mono_memory_write_barrier ();
  96                 top->size++;
  97                 mono_memory_write_barrier ();
  98                 MonoObject **h = &top->objects [idx];
  99                 *h = object;
 100                 return h;
 101         }
 102         if (G_LIKELY (top->next)) {
 103                 top->next->size = 0;
 104                 /* make sure size == 0 is visible to a GC thread before it sees the new top */
 105                 mono_memory_write_barrier ();
 106                 top = top->next;
 107                 handles->top = top;
 108                 goto retry;
 109         }
 110         HandleChunk *new_chunk = g_new (HandleChunk, 1);
 111         new_chunk->size = 0;
 112         new_chunk->prev = top;
 113         new_chunk->next = NULL;
 114         /* make sure size == 0 before new chunk is visible */
 115         mono_memory_write_barrier ();
 116         top->next = new_chunk;
 117         handles->top = new_chunk;
 118         goto retry;
 119 }
 120
 121
 122
 123 HandleStack*
 124 mono_handle_stack_alloc (void)
 125 {
 126         HandleStack *stack = g_new (HandleStack, 1);
 127         HandleChunk *chunk = g_new (HandleChunk, 1);
 128
 129         chunk->size = 0;
 130         chunk->prev = chunk->next = NULL;
 131         mono_memory_write_barrier ();
 132         stack->top = stack->bottom = chunk;
 133         return stack;
 134 }
 135
 136 void
 137 mono_handle_stack_free (HandleStack *stack)
 138 {
 139         if (!stack)
 140                 return;
 141         HandleChunk *c = stack->bottom;
 142         stack->top = stack->bottom = NULL;
 143         mono_memory_write_barrier ();
 144         while (c) {
 145                 HandleChunk *next = c->next;
 146                 g_free (c);
 147                 c = next;
 148         }
 149         g_free (c);
 150         g_free (stack);
 151 }
 152
 153 void
 154 mono_handle_stack_scan (HandleStack *stack, GcScanFunc func, gpointer gc_data)
 155 {
 156         /* if we're running, we know the world is stopped.
 157          */
 158         HandleChunk *cur = stack->bottom;
 159         HandleChunk *last = stack->top;
 160
 161         if (!cur)
 162                 return;
 163
 164         while (cur) {
 165                 int i;
 166                 for (i = 0; i < cur->size; ++i) {
 167                         if (cur->objects [i] != NULL)
 168                                 func ((gpointer*)&cur->objects [i], gc_data);
 169                 }
 170                 if (cur == last)
 171                         break;
 172                 cur = cur->next;
 173         }
 174 }
 175
 176 void
 177 mono_stack_mark_record_size (MonoThreadInfo *info, HandleStackMark *stackmark, const char *func_name)
 178 {
 179         HandleStack *handles = (HandleStack *)info->handle_stack;
 180         HandleChunk *cur = stackmark->chunk;
 181         int size = -stackmark->size; //discard the starting point of the stack
 182         while (cur) {
 183                 size += cur->size;
 184                 if (cur == handles->top)
 185                         break;
 186                 cur = cur->next;
 187         }
 188
 189         if (size > THIS_IS_AN_OK_NUMBER_OF_HANDLES)
 190                 g_warning ("%s USED %d handles\n", func_name, size);
 191 }
 192
 193 /*
 194  * Pop the stack until @stackmark and make @value the top value.
 195  *
 196  * @return the new handle for what @value points to
 197  */
 198 MonoRawHandle
 199 mono_stack_mark_pop_value (MonoThreadInfo *info, HandleStackMark *stackmark, MonoRawHandle value)
 200 {
 201         g_error ("impl me");
 202 }
 203
 204 /* Temporary place for some of the handle enabled wrapper functions*/
 205
 206 MonoStringHandle
 207 mono_string_new_handle (MonoDomain *domain, const char *data, MonoError *error)
 208 {
 209         return MONO_HANDLE_NEW (MonoString, mono_string_new_checked (domain, data, error));
 210 }
 211
 212 MonoArrayHandle
 213 mono_array_new_handle (MonoDomain *domain, MonoClass *eclass, uintptr_t n, MonoError *error)
 214 {
 215         return MONO_HANDLE_NEW (MonoArray, mono_array_new_checked (domain, eclass, n, error));
 216 }
 217
 218 #ifdef ENABLE_CHECKED_BUILD
 219 /* Checked build helpers */
 220 void
 221 mono_handle_verify (MonoRawHandle raw_handle)
 222 {
 223
 224 }
 225 #endif