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9.5 Intertask Communication
1
The primary
means for intertask communication is provided by calls on entries and
protected subprograms. Calls on protected subprograms allow coordinated
access to shared data objects. Entry calls allow for blocking the caller
until a given condition is satisfied (namely, that the corresponding
entry is open -- see
9.5.3), and then communicating
data or control information directly with another task or indirectly
via a shared protected object.
Static Semantics
2
Any
call on an entry or on a protected subprogram identifies a
target
object for the operation, which is either a task (for an entry call)
or a protected object (for an entry call or a protected subprogram call).
The target object is considered an implicit parameter to the operation,
and is determined by the operation
name
(or
prefix) used in the call on
the operation, as follows:
3
- If it is a direct_name
or expanded name that denotes the declaration (or body) of the operation,
then the target object is implicitly specified to be the current instance
of the task or protected unit immediately enclosing the operation; such
a call is defined to be an internal call;
4
- If it
is a selected_component that is
not an expanded name, then the target object is explicitly specified
to be the task or protected object denoted by the prefix
of the name; such
a call is defined to be an external call;
5
- If the name
or prefix is a dereference (implicit
or explicit) of an access-to-protected-subprogram value, then the target
object is determined by the prefix
of the Access attribute_reference
that produced the access value originally, and the call is defined to
be an external call;
6
- If the name
or prefix denotes a subprogram_renaming_declaration,
then the target object is as determined by the name
of the renamed entity.
7
A
corresponding definition of target object applies to a
requeue_statement
(see
9.5.4), with a corresponding distinction
between an
internal requeue and an
external requeue.
Dynamic Semantics
8
Within the body of a protected operation, the
current instance (see
8.6) of the immediately
enclosing protected unit is determined by the target object specified
(implicitly or explicitly) in the call (or requeue) on the protected
operation.
9
Any call on a protected procedure or entry of
a target protected object is defined to be an update to the object, as
is a requeue on such an entry.
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