Re: [dpdk-dev] [PATCH v2] Change alarm cancel function to thread-safe:

["Wodkowski, PawelX" <pawelx.wodkowski@intel.com>]

> -----Original Message-----
> Paweł
> 
> > On Mon, Sep 29, 2014 at 10:11:38AM +0000, Wodkowski, PawelX wrote:
> > > > >
> > > > > Image how you will be damned by someone that not even notice you
> > change
> > > > > and he Is managing some kind of resource based on returned number of
> > > > > set/canceled timers. If you suddenly start returning negative values how
> > those
> > > > > application will behave? Silently changing returned value domain is evil in
> > its
> > > > > pure form.
> > > >
> > > > As I can see the impact is very limited.
> > >
> > > It is small impact to DPDK but can be huge to user application:
> >
> > This is why we traditionally have in the release-notes for each release a
> > section dedicated to calling out changes from one release to another. [See
> > http://dpdk.org/doc/intel/dpdk-release-notes-1.7.0.pdf section 5]. Since
> > from release-to-release there are generally only a couple of changes -
> > though our next release may be a little different - the actual changes are
> > clear enough to read about without wading through pages of documentation.
> I
> > thinking calling out the change in both the release notes and the API docs
> > is sufficient even for a change like this.
> >
> > Basically, I wouldn't let API stability factor in too much in trying to get
> > a proper fix for this issue.
> >
> > /Bruce
> >
> 
> Summarizing all proposed solutions and to be able to produce final patch - what
> Is desired behavior after fix?
> 
> 1. do we leave as is in Patch v2:
> 1.1 if canceling from other thread - if one of the alarms is executing, wait to
>   finish its execution and then cancel any rearmed alarms.
> 1.2 if canceling from alarm handler and one of the alarms to cancel is this
>   executing callback do no wait for it to finish and cancel anything else.
> 
>  in both cases return number of canceled callbacks.
> 
> 2. Do exactly like in 1. but return -EINPROGRESS instead of canceled alarms
>   if one of the alarms to cancel is currently executing callback from alarm thread
>   (information about number of canceled alarms will be lost).

Or instead of returning -EINPROGRESS set errno to EINPROGRESS (replace
returning error value by setting errno and function can always return number
of canceled callbacks - in error condition 0)?

> 
> 3. refuse to cancel anything if canceling currently executing alarm from alarm
>   callback and return -EINPROGRESS otherwise do like in 1.1.
> 
> 4. Implement behaviour 1/2/3 (which?) and add API call to interrogate list of
>   alarms and retrun state of given alarms(s).
> 
> 5. other solutions?
> 
> Pawel