9.8 Abort of a Task - Abort of a Sequence of Statements
Syntax
abort_statement ::= abort task_name {,
task_name};
Name Resolution Rules
Each
task_name
is expected to be of any task type; each can be of a different task type.
Dynamic Semantics
For the execution of an
abort_statement,
the given
task_names
are evaluated in an arbitrary order.
Each
named task is then
aborted, which consists of making the task
abnormal and aborting the execution of the corresponding
task_body,
unless it is already completed.
When
the execution of a construct is
aborted (including that of a
task_body
or of a
sequence_of_statements),
the execution of every construct included within the aborted execution
is also aborted, except for executions included within the execution
of an
abort-deferred operation; the execution of an abort-deferred
operation continues to completion without being affected by the abort;
the following are the abort-deferred operations:
a protected action;
waiting for an entry call to complete (after having
initiated the attempt to cancel it — see below);
waiting for the termination of dependent tasks;
the execution of an Initialize procedure as the
last step of the default initialization of a controlled object;
the execution of a Finalize procedure as part of
the finalization of a controlled object;
an assignment operation to an object with a controlled
part.
The last three of these are discussed further in
7.6.
When a master is aborted, all tasks that depend on
that master are aborted.
If the execution of
an entry call is aborted, an immediate attempt is made to cancel the
entry call (see
9.5.3). If the execution
of a construct is aborted at a time when the execution is blocked, other
than for an entry call, at a point that is outside the execution of an
abort-deferred operation, then the execution of the construct completes
immediately. For an abort due to an
abort_statement,
these immediate effects occur before the execution of the
abort_statement
completes. Other than for these immediate cases, the execution of a construct
that is aborted does not necessarily complete before the
abort_statement
completes. However, the execution of the aborted construct completes
no later than its next
abort completion point (if any) that occurs
outside of an abort-deferred operation;
the following
are abort completion points for an execution:
the point where the execution initiates the activation
of another task;
the end of the activation of a task;
a point within a parallel construct where a new
logical thread of control is created;
the end of a parallel construct;
Bounded (Run-Time) Errors
An attempt to execute an
asynchronous_select
as part of the execution of an abort-deferred operation is a bounded
error. Similarly, an attempt to create a task that depends on a master
that is included entirely within the execution of an abort-deferred operation
is a bounded error.
In both cases, Program_Error
is raised if the error is detected by the implementation; otherwise,
the operations proceed as they would outside an abort-deferred operation,
except that an abort of the
abortable_part
or the created task does not necessarily have an effect.
Erroneous Execution
If
an assignment operation completes prematurely due to an abort, the assignment
is said to be
disrupted; the target of the assignment or its parts
can become abnormal, and certain subsequent uses of the object can be
erroneous, as explained in
13.9.1.
NOTE 1 An
abort_statement
is best used only in situations requiring unconditional termination.
NOTE 2 A task is allowed to abort
any task it can name, including itself.
NOTE 3 Additional requirements associated
with abort are given in
D.6.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe