9.5 Intertask Communication
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
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:
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;
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;
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;
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.
Legality Rules
The view of the target protected object associated
with a call of a protected procedure or entry shall be a variable.
Dynamic Semantics
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.
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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