D.10.1 Synchronous Barriers
1/3
This clause introduces a language-defined package
to synchronously release a group of tasks after the number of blocked
tasks reaches a specified count value.
Static Semantics
2/3
The following language-defined
library package exists:
3/3
package Ada.Synchronous_Barriers
is
pragma Preelaborate(Synchronous_Barriers);
4/3
subtype Barrier_Limit
is Positive
range 1 ..
implementation-defined;
5/3
type Synchronous_Barrier (Release_Threshold : Barrier_Limit)
is limited private;
6/3
procedure Wait_For_Release (The_Barrier :
in out Synchronous_Barrier;
Notified :
out Boolean);
7/3
private
-- not specified by the language
end Ada.Synchronous_Barriers;
8/3
Type Synchronous_Barrier needs finalization (see
7.6).
Dynamic Semantics
9/3
Each call to Wait_For_Release blocks the calling
task until the number of blocked tasks associated with the Synchronous_Barrier
object is equal to Release_Threshold, at which time all blocked tasks
are released. Notified is set to True for one of the released tasks,
and set to False for all other released tasks.
10/3
The mechanism for determining which task sets Notified
to True is implementation defined.
11/3
Once all tasks have been released, a Synchronous_Barrier
object may be reused to block another Release_Threshold number of tasks.
12/3
As the first step of the finalization of a Synchronous_Barrier,
each blocked task is unblocked and Program_Error is raised at the place
of the call to Wait_For_Release.
13/3
It is implementation defined whether an abnormal
task which is waiting on a Synchronous_Barrier object is aborted immediately
or aborted when the tasks waiting on the object are released.
14/3
Wait_For_Release is a potentially blocking operation
(see
9.5.1).
Bounded (Run-Time) Errors
15/3
It is a bounded error to call Wait_For_Release on
a Synchronous_Barrier object after that object is finalized. If the error
is detected, Program_Error is raised. Otherwise, the call proceeds normally,
which may leave a task blocked forever.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe