Re: Advice on abort

[Poul-Erik Andreasen <poulerik@pea.dk>]

Dmitry A. Kazakov wrote:
> On 7 Nov 2005 09:09:53 -0800, REH wrote:
> 
> 
>>Poul-Erik Andreasen wrote:
>>
>>>REH wrote:
>>>
>>>>What are the best options when a task needs to be terminated, but
>>>>signaling the task may not be possible?  We have tasks that sometimes
>>>>need to be terminated, but may potentially be blocked on a resource,
>>>>such as a socket.  Currently we use OS-specific calls to terminate the
>>>>task, but I've never liked that.  I've been thinking of using the abort
>>>>statement, but I don't think that's very graceful either.  I also would
>>>>rather not complicate the code (or force polling behavior) by making
>>>>the sockets non-blocking.  Any advice?
>>>>
>>>
>>>One poosibillty is too use asyncronius transfer of control. Somthing
>>>like this.
>>>
>>>select
>>>    call.foo_entry  -- this i is a guarded entry in a protected
>>>object or 				--	another task
>>>    -- her can you have anything yuo may need to clean up after the abort
>>>then abort
>>>    listen_to_socket  this is the function wich may be blocked
>>>end select
>>>
>>>Thee foo_entry basicly dosen't need to do anything. an you have onother
>>>procedure or entry to open it.
>>>
>>
>>I was once advised never to use ATC because it is very slow.  Is this
>>true?  It was in reference to GNAT.
> 
> 
> That is not the main concern. The problem is the state in which aborting
> would leave the socket and the corresponding port.
I am not that good at sockets, So i vould like to know  wich problematic 
(uncleanable) states wee are taking about.

> Note also that what you want to do is not an Ada issue at all. Actually you
> don't want to abort any Ada task. What you want is to cancel an OS
> operation blocking some Ada task. This can be done *only* by means of the
> OS being under consideration. There are little choices:
> 
> 1. Asynchronous I/O without blocking
> 
> 2. Synchronous I/O with some cancel operation invoked from outside (like
> closing socket, or Abort_Selection proposed by Marc Criley)
> 

This will however require that the sockets or select are made public in 
some way, wich a dont like.


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