Ada 2012 Reference Manual
9.7.2 Timed Entry Calls
A timed_entry_call issues an entry call that is cancelled if the call (or a requeue-with-abort of the call) is not selected before the expiration time is reached. A procedure call may appear rather than an entry call for cases where the procedure might be implemented by an entry.
Syntax
Legality Rules
If a procedure_call_statement is used for a procedure_or_entry_call, the procedure_name or procedure_prefix of the procedure_call_statement shall statically denote an entry renamed as a procedure or (a view of) a primitive subprogram of a limited interface whose first parameter is a controlling parameter (see 3.9.2).
Dynamic Semantics
For the execution of a timed_entry_call, the entry_name, procedure_name, or procedure_prefix, and any actual parameters are evaluated, as for a simple entry call (see 9.5.3) or procedure call (see 6.4). The expiration time (see 9.6) for the call is determined by evaluating the delay_expression of the delay_alternative. If the call is an entry call or a call on a procedure implemented by an entry, the entry call is then issued. Otherwise, the call proceeds as described in 6.4 for a procedure call, followed by the sequence_of_statements of the entry_call_alternative; the sequence_of_statements of the delay_alternative is ignored.
If the call is queued (including due to a requeue-with-abort), and not selected before the expiration time is reached, an attempt to cancel the call is made. If the call completes due to the cancellation, the optional sequence_of_statements of the delay_alternative is executed; if the entry call completes normally, the optional sequence_of_statements of the entry_call_alternative is executed.
Examples
Example of a timed entry call:
select
Controller.Request(Medium)(Some_Item);
or
delay 45.0;
-- controller too busy, try something else
end select;
Controller.Request(Medium)(Some_Item);
or
delay 45.0;
-- controller too busy, try something else
end select;
