Commit eb89d2c9 authored by Michael Lippautz's avatar Michael Lippautz Committed by V8 LUCI CQ

Reland "cppgc: Consistently treat sentinel pointer as live"

This is a reland of commit 60e9b503

Original change's description:
> cppgc: Consistently treat sentinel pointer as live
>
> Sentinel pointers would be treated as live by the GC (through
> `HandleWeak()` but would be treated as dead when checked explicitly
> through the `LivenessBroker` in e.g. custom callbacks.
>
> Treat sentinel pointers as live consistently across all callsites
> and weak types.
>
> Change-Id: I9a4c096ddac1a111df808f3683325b55e7597eea
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3782800
> Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Anton Bikineev <bikineev@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81916}

Change-Id: Ie2476345b9ea8406015a3b07bd6880c1159ede08
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3779913Reviewed-by: 's avatarAnton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: 's avatarOmer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81975}
parent 26230971
...@@ -7,6 +7,7 @@ ...@@ -7,6 +7,7 @@
#include "cppgc/heap.h" #include "cppgc/heap.h"
#include "cppgc/member.h" #include "cppgc/member.h"
#include "cppgc/sentinel-pointer.h"
#include "cppgc/trace-trait.h" #include "cppgc/trace-trait.h"
#include "v8config.h" // NOLINT(build/include_directory) #include "v8config.h" // NOLINT(build/include_directory)
...@@ -44,24 +45,24 @@ class V8_EXPORT LivenessBroker final { ...@@ -44,24 +45,24 @@ class V8_EXPORT LivenessBroker final {
public: public:
template <typename T> template <typename T>
bool IsHeapObjectAlive(const T* object) const { bool IsHeapObjectAlive(const T* object) const {
// nullptr objects are considered alive to allow weakness to be used from // - nullptr objects are considered alive to allow weakness to be used from
// stack while running into a conservative GC. Treating nullptr as dead // stack while running into a conservative GC. Treating nullptr as dead
// would mean that e.g. custom collectins could not be strongified on stack. // would mean that e.g. custom collections could not be strongified on
return !object || // stack.
// - Sentinel pointers are also preserved in weakness and not cleared.
return !object || object == kSentinelPointer ||
IsHeapObjectAliveImpl( IsHeapObjectAliveImpl(
TraceTrait<T>::GetTraceDescriptor(object).base_object_payload); TraceTrait<T>::GetTraceDescriptor(object).base_object_payload);
} }
template <typename T> template <typename T>
bool IsHeapObjectAlive(const WeakMember<T>& weak_member) const { bool IsHeapObjectAlive(const WeakMember<T>& weak_member) const {
return (weak_member != kSentinelPointer) && return IsHeapObjectAlive<T>(weak_member.Get());
IsHeapObjectAlive<T>(weak_member.Get());
} }
template <typename T> template <typename T>
bool IsHeapObjectAlive(const UntracedMember<T>& untraced_member) const { bool IsHeapObjectAlive(const UntracedMember<T>& untraced_member) const {
return (untraced_member != kSentinelPointer) && return IsHeapObjectAlive<T>(untraced_member.Get());
IsHeapObjectAlive<T>(untraced_member.Get());
} }
private: private:
......
...@@ -327,7 +327,6 @@ class V8_EXPORT Visitor { ...@@ -327,7 +327,6 @@ class V8_EXPORT Visitor {
const PointerType* weak = static_cast<const PointerType*>(object); const PointerType* weak = static_cast<const PointerType*>(object);
auto* raw_ptr = weak->GetFromGC(); auto* raw_ptr = weak->GetFromGC();
// Sentinel values are preserved for weak pointers. // Sentinel values are preserved for weak pointers.
if (raw_ptr == kSentinelPointer) return;
if (!info.IsHeapObjectAlive(raw_ptr)) { if (!info.IsHeapObjectAlive(raw_ptr)) {
weak->ClearFromGC(); weak->ClearFromGC();
} }
......
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