1037152 - Use Vector<UniquePtr> instead of Vector<Scoped> for tracking heap edge names

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Jeff Walden [:Waldo]]

Interestingly, this is currently an allocator mismatch -- js_strdup uses cx->malloc which is supposed to be js_free'd, not free'd, as mozilla::ScopedFreePtr does.  No effect except for embedders that override js_free.

Comment 1

[Jeff Walden [:Waldo]]

Attachment: Patch

Note how nicely forgetName() works -- it returns a temporary UniquePtr that Vector painlessly adopts without any special effort needed.  Go rvalue references!

Comment 2

[Jim Blandy :jimb]

Comment on attachment 8454020 [details] [diff] [review]
Patch

Review of attachment 8454020 [details] [diff] [review]:
-----------------------------------------------------------------

::: js/src/builtin/TestingFunctions.cpp
@@ -1688,5 @@
>  
>    public:
>      BackEdge() : name_(nullptr) { }
> -    // Construct an initialized back edge. Take ownership of |name|.
> -    BackEdge(JS::ubi::Node predecessor, jschar *name)

Could you not delete the "Take ownership of |name|" comment? I grant that passing a UniquePtr *always* takes ownership, but I think it should be called out here.

Comment 3

[Jim Blandy :jimb]

> Note how nicely forgetName() works -- it returns a temporary UniquePtr that
> Vector painlessly adopts without any special effort needed.  Go rvalue
> references!

Right, that's the same way that the ScopedFreePtr was handling it, wasn't it?

Comment 4

[Jeff Walden [:Waldo]]

Almost, but not quite.  forgetName was returning a raw pointer.  Someone who did this (or something not nearly so obviously dumb) would leak:

  (void) bedge.forgetName();

whereas now, someone who does that will *not* leak.  If you forget the name, the returned value owns the name, and when it's destroyed (or anything else it hands off the name to) it'll handle things.

Comment 5

[Jeff Walden [:Waldo]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/9c2d9347e6ea

Comment 6

[Ryan VanderMeulen [:RyanVM]]

https://hg.mozilla.org/mozilla-central/rev/9c2d9347e6ea