Re: Tail recursion upon task destruction

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Wed, 18 Nov 2009 11:31:59 +0100, stefan-lucks@see-the.signature wrote:

> On Wed, 18 Nov 2009, Dmitry A. Kazakov wrote:
> 
>> Now consider a case when the last screw is removed from the device. This 
>> is an operation eventually serviced by the device driver. I.e. within 
>> the device driver, you see, it was the last screw of the device and *if* 
>> there is no other references to the device, it must fall apart. This is 
>> a case where you wanted the device to commit suicide. There is nobody 
>> else out there to do this. The device is dangling. This is not the only 
>> use case, just one possible case.
> 
> OK, so you have a task (a device) which notices that it is no longer 
> useful. You would like such a task to do some cleanup and to commit 
> "suicide". Unfortunately, it can't do the cleanup after the "suicide", 
> because it is "dead" then. And it can't cleanup itself before being 
> "dead" because it needs its local memory until the very moment of its 
> "death".
> 
> But couldn't you just use (or maybe abuse) the features from 
> Ada.Task_Termination to do perform the cleanup, after the task has died?
> Even if it the "death" is not by suicide (apart from 
> "suicide" = regular termination, the options are "murder" = abort and
> "accident" = unhandled exception). 
> See <http://www.adaic.org/standards/05rat/html/Rat-5-2.html#I1150>.

Yes, it is an interesting option. One could terminate the task and from the
handler kill the object. The difficulty is that Ada.Task_Termination is not
generic. It is not possible to pass a reference to the object to the
handler.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de