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Reland "cppgc: Consistently treat sentinel pointer as live"

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This is a reland of commit 60e9b50374

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/+/3779913
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81975}
This commit is contained in:
Michael Lippautz 2022-07-22 14:29:06 +02:00 committed by V8 LUCI CQ
parent 2623097138
commit eb89d2c92f
2 changed files with 8 additions and 8 deletions
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15
include/cppgc/liveness-broker.h
View File

@ -7,6 +7,7 @@
#include "cppgc/heap.h"
#include "cppgc/member.h"
#include "cppgc/sentinel-pointer.h"
#include "cppgc/trace-trait.h"
#include "v8config.h" // NOLINT(build/include_directory)
@ -44,24 +45,24 @@ class V8_EXPORT LivenessBroker final {
public:
template <typename T>
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
// would mean that e.g. custom collectins could not be strongified on stack.
return !object ||
// would mean that e.g. custom collections could not be strongified on
// stack.
// - Sentinel pointers are also preserved in weakness and not cleared.
return !object || object == kSentinelPointer ||
IsHeapObjectAliveImpl(
TraceTrait<T>::GetTraceDescriptor(object).base_object_payload);
}
template <typename T>
bool IsHeapObjectAlive(const WeakMember<T>& weak_member) const {
return (weak_member != kSentinelPointer) &&
IsHeapObjectAlive<T>(weak_member.Get());
return IsHeapObjectAlive<T>(weak_member.Get());
}
template <typename T>
bool IsHeapObjectAlive(const UntracedMember<T>& untraced_member) const {
return (untraced_member != kSentinelPointer) &&
IsHeapObjectAlive<T>(untraced_member.Get());
return IsHeapObjectAlive<T>(untraced_member.Get());
}
private:

1
include/cppgc/visitor.h
View File

@ -327,7 +327,6 @@ class V8_EXPORT Visitor {
const PointerType* weak = static_cast<const PointerType*>(object);
auto* raw_ptr = weak->GetFromGC();
// Sentinel values are preserved for weak pointers.
if (raw_ptr == kSentinelPointer) return;
if (!info.IsHeapObjectAlive(raw_ptr)) {
weak->ClearFromGC();
}