On 3/5/2012 3:59 PM, Glenn Maynard wrote:
On Fri, Mar 2, 2012 at 6:54 PM, Feras Moussa <fer...@microsoft.com
<mailto:fer...@microsoft.com>> wrote:
To address this issue, we propose that a close method be added to
the Blob
interface.
When called, the close method should release the underlying
resource of the
Blob, and future operations on the Blob will return a new error, a
ClosedError.
This allows an application to signal when it's finished using the
Blob.
This is exactly like the "neuter" concept, defined at
http://dev.w3.org/html5/spec/common-dom-interfaces.html#transferable-objects.
I recommend using it. Make Blob a Transferable, and have close()
neuter the object. The rest of this wouldn't change much, except
you'd say "if the object has been neutered" (or "has the neutered flag
set", or however it's defined) instead of "if the close method has
been called".
Originally, I think it was assumed that Blobs don't need to be
Transferable, because they're immutable, which means you don't
(necessarily) need to make a copy when transferring them between
threads. That was only considering the cost of copying the Blob,
though, not the costs of delayed GC that you're talking about here, so
I think transferable Blobs do make sense.
Also, the close() method should probably go on Transferable (with a
name less likely to clash, eg. "neuter"), instead of as a one-off on
Blob. If it's useful for Blob, it's probably useful for ArrayBuffer
and all other future Transferables as well.
Glenn,
Do you see old behavior working something like the following?
var blob = new Blob("my new big blob");
var keepBlob = blob.slice();
destination.postMessage(blob, '*', [blob]); // is try/catch needed here?
blob = keepBlob; // keeping a copy of my blob still in thread.
Sorry to cover too many angles: if Blob is Transferable, then it'll
neuter; so if we do want a local copy, we'd use slice ahead of time to
keep it.
And we might have an error on postMessage stashing it in the transfer
array if it's not a Transferable on an older browser.
The new behavior is pretty easy.
var blob = new Blob("my big blob");
blob.close(); // My blob has been neutered before it could procreate.
-Charles
