Abort of a Task - Abort of a Sequence of Statements
Author: JTC1/SC22/WG9/ARG, by Randall Brukardt, ARG Editor

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# 9.8 Abort of a Task - Abort of a Sequence of Statements

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An abort_statement causes one or more tasks to become abnormal, thus preventing any further interaction with such tasks. The completion of the triggering_statement of an asynchronous_select causes a sequence_of_statements to be aborted.

#### Syntax

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abort_statement ::= abort task_name {, task_name};

#### Name Resolution Rules

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Each task_name is expected to be of any task type; they need not all be of the same task type.

#### Dynamic Semantics

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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.
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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:
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- a protected action;

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- waiting for an entry call to complete (after having initiated the attempt to cancel it -- see below);

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- waiting for the termination of dependent tasks;

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- the execution of an Initialize procedure as the last step of the default initialization of a controlled object;

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- the execution of a Finalize procedure as part of the finalization of a controlled object;

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- an assignment operation to an object with a controlled part.

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The last three of these are discussed further in 7.6.
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When a master is aborted, all tasks that depend on that master are aborted.
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The order in which tasks become abnormal as the result of an abort_statement or the abort of a sequence_of_statements is not specified by the language.
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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:
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- the point where the execution initiates the activation of another task;

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- the end of the activation of a task;

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- the start or end of the execution of an entry call, accept_statement, delay_statement, or abort_statement;

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- the start of the execution of a select_statement, or of the sequence_of_statements of an exception_handler.

#### Bounded (Run-Time) Errors

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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 might or might not have an effect.

#### Erroneous Execution

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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.
NOTES
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38 An abort_statement should be used only in situations requiring unconditional termination.
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39 A task is allowed to abort any task it can name, including itself.
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40 Additional requirements associated with abort are given in D.6, ``Preemptive Abort''.

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