Re: Advantages

[Brian May <bam@snoopy.apana.org.au>]

>>>>> "Randy" == Randy Brukardt <randy@rrsoftware.com> writes:

    Randy> That's correct. And it makes sense to allow I/O, as many
    Randy> implementation don't in fact do anything blocking. But I
    Randy> would expect that the implementation would treat things
    Randy> that are *known* to be blocking (like a delay statement)
    Randy> differently - there can be no legitimate reason for doing
    Randy> that. In a ceiling locking implementation, blocking would

<hat mode="devils advocate">

You want to send a message to a hardware device. The requirements
specify that one message should be sent to the device, followed by a
fixed delay, then another message. During this entire period of time,
exclusive access is required to the device, because other threads
could otherwise interfere.

Lets also assume that sending the message is a blocking function that
will block until either an acknowledgement or error is returned by the
device.

What is the safest way of implementing this under Ada?

Three blocking statements, that require exclusive access to a
resource.

You could have a protected type emulate a semaphore, but then we are
back to using primitive operations (and related mistakes) that Ada was
meant to avoid.

You could have these 3 statements run from a procedure within a
protected type (along with procedures to do other things), but you not
suppose to make calls that potentially block from a protected type.

Just curious as to the recommended way of dealing with this
situation...

</hat>
-- 
Brian May <bam@snoopy.apana.org.au>