9.7.3 Conditional Entry Calls
1/2
{
AI95-00345-01}
[A
conditional_entry_call issues an entry
call that is then cancelled if it is not selected immediately (or if
a requeue-with-abort of the call is not selected immediately).
A procedure call may appear rather than an entry call for cases where
the procedure might be implemented by an entry. ]
1.a
To be honest: In the case of an entry
call on a protected object, it is OK if the entry is closed at the start
of the corresponding protected action, so long as it opens and the call
is selected before the end of that protected action (due to changes in
the Count attribute).
Syntax
2
conditional_entry_call ::=
select
entry_call_alternative
else
sequence_of_statements
end select;
Dynamic Semantics
3
{execution (conditional_entry_call)
[partial]} The execution of a
conditional_entry_call
is defined to be equivalent to the execution of a
timed_entry_call
with a
delay_alternative specifying an immediate
expiration time and the same
sequence_of_statements
as given after the reserved word
else.
4
40 A conditional_entry_call
may briefly increase the Count attribute of the entry, even if the conditional
call is not selected.
Examples
5
Example of a conditional
entry call:
6
procedure Spin(R : in Resource) is
begin
loop
select
R.Seize;
return;
else
null; -- busy waiting
end select;
end loop;
end;
Wording Changes from Ada 83
6.a
This clause comes after the one for Timed Entry
Calls, so we can define conditional entry calls in terms of timed entry
calls. We do that so that an "expiration time" is defined for
both, thereby simplifying the definition of what happens on a requeue-with-abort.
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