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<H1> D.6 Preemptive Abort</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [This clause specifies requirements on the immediacy
with which an aborted construct is completed.] </DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> On a system with a single processor, an aborted
construct is completed immediately at the first point that is outside
the execution of an abort-deferred operation.</DIV>
<H4 ALIGN=CENTER>Documentation Requirements</H4>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> On a multiprocessor, the implementation shall
document any conditions that cause the completion of an aborted construct
to be delayed later than what is specified for a single processor. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>On
a multiprocessor, any conditions that cause the completion of an aborted
construct to be delayed later than what is specified for a single processor.</FONT></DIV>
<H4 ALIGN=CENTER>Metrics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The implementation
shall document the following metrics: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>The execution time, in processor clock cycles, that it
takes for an <FONT FACE="Arial, Helvetica">abort_statement</FONT> to
cause the completion of the aborted task. This is measured in a situation
where a task T2 preempts task T1 and aborts T1. T1 does not have any
finalization code. T2 shall verify that T1 has terminated, by means of
the Terminated attribute.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>On a multiprocessor, an upper bound in seconds, on the
time that the completion of an aborted task can be delayed beyond the
point that it is required for a single processor.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An upper bound on the execution time of an <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>,
in processor clock cycles. This is measured between a point immediately
before a task T1 executes a protected operation Pr.Set that makes the
<FONT FACE="Arial, Helvetica">condition</FONT> of an <FONT FACE="Arial, Helvetica">entry_barrier</FONT>
Pr.Wait true, and the point where task T2 resumes execution immediately
after an entry call to Pr.Wait in an <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>.
T1 preempts T2 while T2 is executing the abortable part, and then blocks
itself so that T2 can execute. The execution time of T1 is measured separately,
and subtracted.</LI></UL>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<UL Class="Bulleted"><LI TYPE=DISC>An upper bound on the execution time of an <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>,
in the case that no asynchronous transfer of control takes place. This
is measured between a point immediately before a task executes the <FONT FACE="Arial, Helvetica">asynchronous_select</FONT>
with a nonnull abortable part, and the point where the task continues
execution immediately after it. The execution time of the abortable part
is subtracted. </LI></UL>
<H4 ALIGN=CENTER>Implementation Advice</H4>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> Even though the <FONT FACE="Arial, Helvetica">abort_statement</FONT>
is included in the list of potentially blocking operations (see <A HREF="AA-9-5-1.html">9.5.1</A>),
it is recommended that this statement be implemented in a way that never
requires the task executing the <FONT FACE="Arial, Helvetica">abort_statement</FONT>
to block.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> On a multi-processor, the delay associated with
aborting a task on another processor should be bounded; the implementation
should use periodic polling, if necessary, to achieve this.</DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>27 Abortion does not change
the active or base priority of the aborted task.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>28 Abortion cannot be more
immediate than is allowed by the rules for deferral of abortion during
finalization and in protected actions.</FONT></DIV>
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