Bug 211669 – Add iterator checking to ListHashSet

• Status: RESOLVED
• Resolution: FIXED
• Component: New Bugs

[Darin Adler]

Add iterator checking to ListHashSet

[Darin Adler]

Created attachment 398934 [details]
Patch

[Anders Carlsson]

Comment on attachment 398934 [details]
Patch

Is WeakPtr thread safe?

[Darin Adler]

(In reply to Anders Carlsson from comment #2)
> Is WeakPtr thread safe?

It uses ThreadSafeRefCounted, so I think yes.

[EWS]

Committed r261440: <https://trac.webkit.org/changeset/261440>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 398934 [details].

[Radar WebKit Bug Importer]

<rdar://problem/63057348>

[Yusuke Suzuki]

(In reply to Darin Adler from comment #3)
> (In reply to Anders Carlsson from comment #2)
> > Is WeakPtr thread safe?
> 
> It uses ThreadSafeRefCounted, so I think yes.

WeakPtr<T>::get returns weird results in multi-threaded environment. This is slightly different from `std::weak_ptr<T>::lock()`.
So, in general, it is not encouraged that we use WeakPtr<T> in multi-threading use because it does not work as expected.
However, in this use case, it is OK.

1. T inherits CanMakeWeakPtr<T> and ThreadSafeRefCounted<T>.
2. In thread A, we create Ref<T>.
3. In thread A, we create WeakPtr<T> from Ref<T>
4. We pass WeakPtr<T> to another thread B.
5. B thread is attempting to call WeakPtr<T>::get().
6. At the same time, in thread A, we start destroying Ref<T>.
7. Before (6) calls WeakPtrImpl::clear(), (5) gets a non nullptr T*.
8. Just after (5) gets non nullptr T*, (7) destroys Ref<T> completely.

WeakPtr<T>::get can return a non-nullptr even if the obtained T* is half-destroyed right now.
So, it is possible that we could miss some cases that T* is already destroyed while WeakPtr<T>::get returns non-nullptr.
But since this is for assertion, false-negative is OK.

[Ryan Haddad]

Reverted r261440 for reason:

Caused 6 TestWTF.WTF failures

Committed r261486: <https://trac.webkit.org/changeset/261486>

[Darin Adler]

Created attachment 399092 [details]
Patch

[Darin Adler]

This new patch fixes the TestWTF.WTF failures. Would appreciate review since more has changed now.

[Darin Adler]

Created attachment 399100 [details]
Patch

[EWS]

Committed r261818: <https://trac.webkit.org/changeset/261818>

All reviewed patches have been landed. Closing bug and clearing flags on attachment 399100 [details].