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9.2 Task Execution - Task Activation
The execution of a task of
a given task type consists of the execution of the corresponding task_body
initial part of this execution is called the activation
task; it consists of the elaboration of the declarative_part
of the task_body
an exception be propagated by the elaboration of its declarative_part
the activation of the task is defined to have failed
, and it becomes
a completed task.
A task object (which represents one task) can
be created either as part of the elaboration of an object_declaration
occurring immediately within some declarative region, or as part of the
evaluation of an allocator. All
tasks created by the elaboration of object_declarations
of a single declarative region (including subcomponents of the declared
objects) are activated together. Similarly, all tasks created by the
evaluation of a single allocator
are activated together. The activation of a task is associated with the
innermost allocator or object_declaration
that is responsible for its creation.
For tasks created by the elaboration of object_declaration
of a given declarative region, the activations are initiated within the
context of the handled_sequence_of_statements
(and its associated exception_handler
if any -- see 11.2
), just prior to executing
the statements of the _sequence
For a package without an explicit body or an explicit handled_sequence_of_statements
an implicit body or an implicit null_statement
is assumed, as defined in 7.2
For tasks created by the evaluation of an allocator,
the activations are initiated as the last step of evaluating the allocator,
after completing any initialization for the object created by the allocator,
and prior to returning the new access value.
that created the new tasks and initiated their activations (the activator
is blocked until all of these activations complete (successfully or not).
Once all of these activations are complete, if the
activation of any of the tasks has failed (due to the propagation of
an exception), Tasking_Error is raised in the activator, at the place
at which it initiated the activations. Otherwise, the activator proceeds
with its execution normally. Any tasks that are aborted prior to completing
their activation are ignored when determining whether to raise Tasking_Error.
Should the task that created the new tasks never
reach the point where it would initiate the activations (due to an abort
or the raising of an exception), the newly created tasks become terminated
and are never activated.
5 An entry of a task can
be called before the task has been activated.
6 If several tasks are
activated together, the execution of any of these tasks need not await
the end of the activation of the other tasks.
7 A task can become completed
during its activation either because of an exception or because it is
aborted (see 9.8).
Example of task
procedure P is
A, B : Server; -- elaborate the task objects A, B
C : Server; -- elaborate the task object C
-- the tasks A, B, C are activated together before the first statement
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