hphp/runtime/base/weakref-data.cpp

   1 /*
   2    +----------------------------------------------------------------------+
   3    | HipHop for PHP                                                       |
   4    +----------------------------------------------------------------------+
   5    | Copyright (c) 2010-present Facebook, Inc. (http://www.facebook.com)  |
   6    +----------------------------------------------------------------------+
   7    | This source file is subject to version 3.01 of the PHP license,      |
   8    | that is bundled with this package in the file LICENSE, and is        |
   9    | available through the world-wide-web at the following url:           |
  10    | http://www.php.net/license/3_01.txt                                  |
  11    | If you did not receive a copy of the PHP license and are unable to   |
  12    | obtain it through the world-wide-web, please send a note to          |
  13    | license@php.net so we can mail you a copy immediately.               |
  14    +----------------------------------------------------------------------+
  15 */
  16 #include "hphp/runtime/base/weakref-data.h"
  17
  18 #include "hphp/runtime/base/string-hash-map.h"
  19 #include "hphp/runtime/base/tv-refcount.h"
  20 #include "hphp/runtime/base/type-object.h"
  21 #include "hphp/runtime/base/type-variant.h"
  22 #include "hphp/system/systemlib.h"
  23 #include "hphp/util/rds-local.h"
  24
  25 namespace HPHP {
  26
  27 // Maps object ids to the WeakRefData associated to them.
  28 using weakref_data_map = req::fast_map<uintptr_t, req::weak_ptr<WeakRefData>>;
  29 RDS_LOCAL(weakref_data_map, s_weakref_data);
  30
  31 void weakref_cleanup() {
  32   s_weakref_data.destroy();
  33 }
  34
  35 void WeakRefData::invalidateWeakRef(uintptr_t ptr) {
  36   auto weakmap = s_weakref_data.get();
  37   auto map_entry = weakmap->find(ptr);
  38   if (map_entry != weakmap->end()) {
  39     map_entry->second.lock()->pointee = make_tv<KindOfUninit>();
  40     weakmap->erase(map_entry);
  41   }
  42 }
  43
  44 req::shared_ptr<WeakRefData> WeakRefData::forObject(Object obj) {
  45   req::shared_ptr<WeakRefData> wr_data;
  46
  47   auto weakmap = s_weakref_data.get();
  48
  49   auto map_entry = weakmap->find((uintptr_t)obj.get());
  50   if (map_entry != weakmap->end()) {
  51     wr_data = map_entry->second.lock();
  52   } else {
  53     wr_data = req::make_shared<WeakRefData>(make_tv<KindOfObject>(obj.get()));
  54
  55     obj->setWeakRefed();
  56     req::weak_ptr<WeakRefData> weak_data = req::weak_ptr<WeakRefData>(wr_data);
  57     auto const DEBUG_ONLY result = weakmap->emplace(
  58       reinterpret_cast<uintptr_t>(obj.get()),
  59       weak_data
  60     );
  61     // Failure. Key should be unique.  We just checked.
  62     assertx(result.second);
  63   }
  64   return wr_data;
  65 }
  66
  67 WeakRefData::~WeakRefData() {
  68   if (type(pointee) != KindOfUninit) {
  69     s_weakref_data.get()->erase(reinterpret_cast<uintptr_t>(val(pointee).pobj));
  70   }
  71 }
  72
  73 /**
  74  * The problem this logic tries to solve:
  75  * - We have a weakref object that points to an object.
  76  * - We use DecRefNZ to get the reference count of the object down to 0 but it
  77  *   hasn't been destructed or sweeped yet. But the GC could sweep it at any
  78  *   moment.
  79  * - Some code now call valid() or get() which without the refcount check would
  80  *   return true or the object.
  81  * - Because we know that if the sweep or destructor had run the pointer would
  82  *   have been cleaned up so if we have a pointer it is safe to look at the
  83  *   object.
  84  * - So we look at the refcount of the object and make sure it is > 0.
  85  */
  86 bool WeakRefData::isValid() const {
  87   auto const ty = type(pointee);
  88   return LIKELY(isRefcountedType(ty))
  89     ? tvGetCount(pointee) > 0
  90     : ty != KindOfUninit;
  91 }
  92
  93 } // namespace HPHP