Timed Entry Calls
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

Ada Reference Manual — Legal Information

# 9.7.2 Timed Entry Calls

1/2
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

2
timed_entry_call ::=
select
entry_call_alternative
or
delay_alternative
end select;
3/2
entry_call_alternative ::=
procedure_or_entry_call [sequence_of_statements]
3.1/2
procedure_or_entry_call ::=
procedure_call_statement | entry_call_statement

#### Legality Rules

3.2/2
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).

#### Static Semantics

3.3/2
If a procedure_call_statement is used for a procedure_or_entry_call, and the procedure is implemented by an entry, then the procedure_ name, or procedure_ prefix and possibly the first parameter of the procedure_call_statement, determine the target object of the call and the entry to be called.

#### Dynamic Semantics

4/2
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.
5
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

6
Example of a timed entry call:
7
select
Controller.Request(Medium)(Some_Item);
or
delay 45.0;
-- controller too busy, try something else
end select;

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