Re: [Qemu-block] [RFC PATCH] coroutines: generate wrapper code

[Vladimir Sementsov-Ogievskiy]

11.02.2019 6:42, Stefan Hajnoczi wrote:
> On Fri, Feb 08, 2019 at 05:11:22PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>> Hi all!
>>
>> We have a very frequent pattern of wrapping a coroutine_fn function
>> to be called from non-coroutine context:
>>
>>    - create structure to pack parameters
>>    - create function to call original function taking parameters from
>>      struct
>>    - create wrapper, which in case of non-coroutine context will
>>      create a coroutine, enter it and start poll-loop.
>>
>> Here is a draft of template code + example how it can be used to drop a
>> lot of similar code.
>>
>> Hope someone like it except me)
> 
> My 2 cents.  Cons:
> 
>   * Synchronous poll loops are an anti-pattern.  They block all of QEMU
>     with the big mutex held.  Making them easier to write is
>     questionable because we should aim to have as few of these as
>     possible.

Understand. Do we have a concept or a kind of target for a future to get rid of
these a lot of poll-loops? What is the right way? At least for block-layer?

> 
>   * Code generation makes the code easier to write but harder to read.
>     Code is read more than written.  In this case I think open coding
>     isn't too bad and I prefer it to reading a code generation script to
>     understand how it works.

But you can read generated code in same way. You only need to read generator
script if it generates something wrong, but should be rare.

> 
> If we were planning to add lots more of these then I agree code
> generation would help.  But in this case I'd rather not.
> 

What do you think at least of generating code to create a coroutine from a 
function
with multiple arguments?

-- 
Best regards,
Vladimir