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Re: Making QEMU easier for management tools and applications

From: Markus Armbruster
Subject: Re: Making QEMU easier for management tools and applications
Date: Fri, 24 Jan 2020 07:38:11 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux)

John Snow <address@hidden> writes:

> On 1/23/20 2:19 AM, Markus Armbruster wrote:
>> Any conventional parser can be made streaming by turning it into a
>> coroutine.  This is probably the simplest solution for handwritten
>> streaming LL parsers, because it permits recursive descent.  In Python,
>> I'd try a generator.
>> Our actual solution for QMP predates coroutine support in QEMU, and is
>> rather hamfisted:
>> * Streaming lexer: it gets fed characters one at a time, and when its
>>   state machine says "token complete", it feeds the token to the
>>   "streamer".
>> * "Streamer": gets fed tokens one at a time, buffers them up counting
>>   curly and square bracket nesting until the nesting is zero, then
>>   passes the buffered tokens to the parser.
>> * Non-streaming parser: it gets fed a sequence of tokens that constitute
>>   a full expression.
>> The best I can say about this is that it works.  The streamer's token
>> buffer eats a lot of memory compared to a real streaming parser, but in
>> practice, it's a drop in the bucket.
> I looked into this at one point. I forget why I didn't like it. I had

Because it's confusing?  Took me a while to get used to it.

> some notion that I should replace this one too, but forget exactly why.
> Maybe it wasn't that bad, if I've forgotten.

Bigger fish to fry.


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