Re: [quicwg/base-drafts] Define INITIAL_PRIORITY frame and remove exclusive dependencies (#2075)

[Martin Thomson <[e-mail]>]

martinthomson commented on this pull request.

I don't know if the exclusive thing need to be bundled in here.

There needs to be more text in this about managing races with PRIORITY frames.  You have resolved the question of which one takes precedence, but you should mention that the identified dependency might have default priority when this is received, resulting in potentially inconsistent prioritization.  Not a big problem, but worth noting I think.

@ddragana, do you know if we use the exclusive thing in our priority setup at all?

> @@ -496,13 +496,9 @@ The PRIORITY frame payload has the following fields:
   : A two-bit field indicating the type of element being depended on.
 
   Empty:
-  : A three-bit field which MUST be zero when sent and MUST be ignored
+  : A four-bit field which MUST be zero when sent and MUST be ignored
     on receipt.

Not really for this, but do we have to mandate ignoring reserved fields?

> +
+~~~~~~~~~~  drawing
+ 0                   1                   2                   3
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|DT |   Empty   |           Element Dependency ID (i)         ...
++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+|   Weight (8)  |
++-+-+-+-+-+-+-+-+
+~~~~~~~~~~
+{: #fig-initial-priority title="INITIAL_PRIORITY frame payload"}
+
+The INITIAL_PRIORITY frame payload has the following fields:
+
+  Dependency Type:
+  : A two-bit field indicating the type of element being depended on.

The alignment of the dependency type in comparison to PRIORITY is unfortunate.

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