Re: [Qemu-devel] [PATCH 1/3] Introduce threadlets

[Stefan Hajnoczi]

On Thu, Oct 14, 2010 at 5:16 PM, Avi Kivity <address@hidden> wrote:
>  On 10/14/2010 11:15 AM, Stefan Hajnoczi wrote:
>>
>> I forgot to add that the semantics of cancellation make it difficult
>> to write correct user code.  Every cancellation user needs to add
>> extra synchronization after the cancel call to handle the case where
>> the work is currently executing.
>>
>> This seems tricky to me and I suspect code using this interface will
>> be buggy.  How about the following?
>> 1. Add a return value indicating that the work is currently executing
>> (this still requires the caller to add extra synchronization but is at
>> least explicit) versus work is no longer on the list.
>> 2. Add a flag to block until the work has been cancelled or completed.
>>  This is useful to callers who are allowed to block.
>
> Blocking is somewhat against the spirit of the thing, no?  While I agree
> that the current cancel API is hard to use correctly, blocking defeats the
> purpose of the API.

Yes, that's why it would have to be an optional flag or a separate
function.  The idea is that callers who are able to block on
cancellation can use common code instead of implementing it from
scratch each time.

Stefan