1567461 - Prevent ModuloBuffer copying, fix moving

Status: RESOLVED FIXED

(Core :: Gecko Profiler, defect, P1)

Description

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

ModuloBuffer may own the underlying byte buffer and may delete it as needed.
If copied or moved, both ModuloBuffer will try to free the resource.

• Copies should just be prevented (like UniquePtr).
• Moves should ensure that the moved-from ModuloBuffer won't delete the resource.

Comment 1

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Attachment: Bug 1567461 - Ensure ModuloBuffer can be properly move-constructed - r?gregtatum

Without declaring them, ModuloBuffer had its copy&move constructor&assignments
defaulted. This means it could have been copied, and then both objects would now
own the same resource and attempt to free it on destruction!

So now:

• Copy construction&assignment are now explicitly disallowed.
• Move assignment is disallowed, to keep some members const.
• Move construction is allowed (so a function can return a ModuloBuffer), and
  ensures that the moved-from object won't free the resource anymore.

Bonus: mBuffer is now const -- because it can be(!)
So ModuloBuffer is like an unchanging resource, but it allows to be moved-from
as an xvalue that should not be used after the move.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/74908c04ec0e
Ensure ModuloBuffer can be properly move-constructed - r=gregtatum

Comment 3

[Andreea Pavel [:apavel]]

https://hg.mozilla.org/mozilla-central/rev/74908c04ec0e