js/src/vm/Watchtower.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
   2  * vim: set ts=8 sts=2 et sw=2 tw=80:
   3  * This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef vm_Watchtower_h
   8 #define vm_Watchtower_h
   9
  10 #include "js/TypeDecls.h"
  11 #include "vm/NativeObject.h"
  12
  13 namespace js {
  14
  15 // [SMDOC] Watchtower
  16 //
  17 // Watchtower is a framework to hook into changes to certain objects. This gives
  18 // us the ability to, for instance, invalidate caches or purge Warp code on
  19 // object layout changes.
  20 //
  21 // Watchtower is only used for objects with certain ObjectFlags set on the
  22 // Shape. This minimizes performance overhead for most objects.
  23 //
  24 // We currently use Watchtower for:
  25 //
  26 // - Invalidating the shape teleporting optimization. See the "Shape Teleporting
  27 //   Optimization" SMDOC comment in CacheIR.cpp.
  28 //
  29 // - Invalidating the MegamorphicCache, a property lookup cache for megamorphic
  30 //   property accesses. See the SMDOC comment in vm/Caches.h.
  31 //
  32 // There's also a testing mechanism that lets us write tests for Watchtower
  33 // hooks. See setWatchtowerCallback and addWatchtowerTarget defined in
  34 // TestingFunctions.cpp.
  35 class Watchtower {
  36   static bool watchPropertyAddSlow(JSContext* cx, Handle<NativeObject*> obj,
  37                                    HandleId id);
  38   static bool watchPropertyRemoveSlow(JSContext* cx, Handle<NativeObject*> obj,
  39                                       HandleId id);
  40   static bool watchPropertyChangeSlow(JSContext* cx, Handle<NativeObject*> obj,
  41                                       HandleId id, PropertyFlags flags);
  42   template <AllowGC allowGC>
  43   static bool watchPropertyModificationSlow(
  44       JSContext* cx,
  45       typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
  46       typename MaybeRooted<PropertyKey, allowGC>::HandleType id);
  47   static bool watchFreezeOrSealSlow(JSContext* cx, Handle<NativeObject*> obj);
  48   static bool watchProtoChangeSlow(JSContext* cx, HandleObject obj);
  49   static bool watchObjectSwapSlow(JSContext* cx, HandleObject a,
  50                                   HandleObject b);
  51
  52  public:
  53   static bool watchesPropertyAdd(NativeObject* obj) {
  54     return obj->hasAnyFlag(
  55         {ObjectFlag::IsUsedAsPrototype, ObjectFlag::UseWatchtowerTestingLog});
  56   }
  57   static bool watchesPropertyRemove(NativeObject* obj) {
  58     return obj->hasAnyFlag(
  59         {ObjectFlag::IsUsedAsPrototype, ObjectFlag::GenerationCountedGlobal,
  60          ObjectFlag::UseWatchtowerTestingLog, ObjectFlag::HasFuseProperty});
  61   }
  62   static bool watchesPropertyChange(NativeObject* obj) {
  63     return obj->hasAnyFlag(
  64         {ObjectFlag::IsUsedAsPrototype, ObjectFlag::GenerationCountedGlobal,
  65          ObjectFlag::HasFuseProperty, ObjectFlag::UseWatchtowerTestingLog});
  66   }
  67   static bool watchesPropertyModification(NativeObject* obj) {
  68     return obj->hasAnyFlag(
  69         {ObjectFlag::HasFuseProperty, ObjectFlag::UseWatchtowerTestingLog});
  70   }
  71   static bool watchesFreezeOrSeal(NativeObject* obj) {
  72     return obj->hasAnyFlag({ObjectFlag::UseWatchtowerTestingLog});
  73   }
  74   static bool watchesProtoChange(JSObject* obj) {
  75     return obj->hasAnyFlag(
  76         {ObjectFlag::IsUsedAsPrototype, ObjectFlag::UseWatchtowerTestingLog});
  77   }
  78   static bool watchesObjectSwap(JSObject* a, JSObject* b) {
  79     auto watches = [](JSObject* obj) {
  80       return obj->hasAnyFlag(
  81           {ObjectFlag::IsUsedAsPrototype, ObjectFlag::UseWatchtowerTestingLog});
  82     };
  83     return watches(a) || watches(b);
  84   }
  85
  86   static bool watchPropertyAdd(JSContext* cx, Handle<NativeObject*> obj,
  87                                HandleId id) {
  88     if (MOZ_LIKELY(!watchesPropertyAdd(obj))) {
  89       return true;
  90     }
  91     return watchPropertyAddSlow(cx, obj, id);
  92   }
  93   static bool watchPropertyRemove(JSContext* cx, Handle<NativeObject*> obj,
  94                                   HandleId id) {
  95     if (MOZ_LIKELY(!watchesPropertyRemove(obj))) {
  96       return true;
  97     }
  98     return watchPropertyRemoveSlow(cx, obj, id);
  99   }
 100   static bool watchPropertyChange(JSContext* cx, Handle<NativeObject*> obj,
 101                                   HandleId id, PropertyFlags flags) {
 102     if (MOZ_LIKELY(!watchesPropertyChange(obj))) {
 103       return true;
 104     }
 105     return watchPropertyChangeSlow(cx, obj, id, flags);
 106   }
 107
 108   // Note: We can only watch property modification for regular object slots
 109   // with an id, not reserved slots.
 110   template <AllowGC allowGC>
 111   static bool watchPropertyModification(
 112       JSContext* cx,
 113       typename MaybeRooted<NativeObject*, allowGC>::HandleType obj,
 114       typename MaybeRooted<PropertyKey, allowGC>::HandleType id) {
 115     if (MOZ_LIKELY(!watchesPropertyModification(obj))) {
 116       return true;
 117     }
 118     return watchPropertyModificationSlow<allowGC>(cx, obj, id);
 119   }
 120   static bool watchFreezeOrSeal(JSContext* cx, Handle<NativeObject*> obj) {
 121     if (MOZ_LIKELY(!watchesFreezeOrSeal(obj))) {
 122       return true;
 123     }
 124     return watchFreezeOrSealSlow(cx, obj);
 125   }
 126   static bool watchProtoChange(JSContext* cx, HandleObject obj) {
 127     if (MOZ_LIKELY(!watchesProtoChange(obj))) {
 128       return true;
 129     }
 130     return watchProtoChangeSlow(cx, obj);
 131   }
 132
 133   static bool watchObjectSwap(JSContext* cx, HandleObject a, HandleObject b) {
 134     if (MOZ_LIKELY(!watchesObjectSwap(a, b))) {
 135       return true;
 136     }
 137     return watchObjectSwapSlow(cx, a, b);
 138   }
 139 };
 140
 141 }  // namespace js
 142
 143 #endif /* vm_Watchtower_h */