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<H1> C.7.1 The Package Task_Identification</H1>
<H4 ALIGN=CENTER>Static Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The following language-defined
library package exists: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Examples"><TT><B>package</B> Ada.Task_Identification <B>is</B><A NAME="I6715"></A><A NAME="I6716"></A><A NAME="I6717"></A><BR>
<B>type</B> <A NAME="I6718"></A><A NAME="I6719"></A>Task_ID <B>is</B> <B>private</B>;<BR>
<A NAME="I6720"></A><A NAME="I6721"></A>Null_Task_ID : <B>constant</B> Task_ID;<BR>
<B>function</B> "=" (Left, Right : Task_ID) <B>return</B> Boolean;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3/1</FONT></DIV>
<DIV Class="Examples"><TT>{<I><A HREF="defect1.html#8652/0070">8652/0070</A></I>}
<BR>
<B>function</B> <A NAME="I6722"></A><A NAME="I6723"></A>Image (T : Task_ID) <B>return</B> String;<BR>
<B>function</B> <A NAME="I6724"></A><A NAME="I6725"></A>Current_Task <B>return</B> Task_ID;<BR>
<B>procedure</B> <A NAME="I6726"></A><A NAME="I6727"></A>Abort_Task (T : <B>in</B> <S><B>out</B> </S>Task_ID);</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Examples"><TT> <B>function</B> <A NAME="I6728"></A><A NAME="I6729"></A>Is_Terminated(T : Task_ID) <B>return</B> Boolean;<BR>
<B>function</B> <A NAME="I6730"></A><A NAME="I6731"></A>Is_Callable (T : Task_ID) <B>return</B> Boolean;<BR>
<B>private</B><BR>
... -- <I>not specified by the language</I><BR>
<B>end</B> Ada.Task_Identification;</TT></DIV>
<H4 ALIGN=CENTER>Dynamic Semantics</H4>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Normal"> A value of the type Task_ID identifies an existent
task. The constant Null_Task_ID does not identify any task. Each object
of the type Task_ID is default initialized to the value of Null_Task_ID.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Normal"> The function "=" returns True if and
only if Left and Right identify the same task or both have the value
Null_Task_ID.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal"> The function Image returns an implementation-defined
string that identifies T. If T equals Null_Task_ID, Image returns an
empty string. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
result of the Task_Identification.Image attribute.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Normal"> The function Current_Task returns a value that
identifies the calling task.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Normal"> The effect of Abort_Task is the same as the <FONT FACE="Arial, Helvetica">abort_statement</FONT>
for the task identified by T. [In addition, if T identifies the environment
task, the entire partition is aborted, See <A HREF="AA-E-1.html">E.1</A>.]</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Normal"> The functions Is_Terminated and Is_Callable return
the value of the corresponding attribute of the task identified by T.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10.a.1/1</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>{<I><A HREF="defect2.html#8652/0115">8652/0115</A></I>}
<U>These routines can be called with an argument identifying the environment
task. Is_Terminated will always be False for such a call, but Is_Callable
(usually True) could be False if the environment task is waiting for
the termination of dependent tasks. Thus, a dependent task can use Is_Callable
to determine if the main subprogram has completed.</U> </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>11</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> For a <FONT FACE="Arial, Helvetica">prefix</FONT>
T that is of a task type [(after any implicit dereference)], the following
attribute is defined: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>12</FONT></DIV>
<DL Class="Hanging"><DT> T'Identity<DD Class="Hanging">
<A NAME="I6732"></A><A NAME="I6733"></A>Yields a value of the type Task_ID
that identifies the task denoted by T.</DL>
<DIV Class="Paranum"><FONT SIZE=-2>13</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> For a <FONT FACE="Arial, Helvetica">prefix</FONT>
E that denotes an <FONT FACE="Arial, Helvetica">entry_declaration</FONT>,
the following attribute is defined: </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>14</FONT></DIV>
<DL Class="Hanging"><DT> E'Caller<DD Class="Hanging">
<A NAME="I6734"></A><A NAME="I6735"></A>Yields a value of the type Task_ID
that identifies the task whose call is now being serviced. Use of this
attribute is allowed only inside an <FONT FACE="Arial, Helvetica">entry_body</FONT>
or <FONT FACE="Arial, Helvetica">accept_statement</FONT> corresponding
to the <FONT FACE="Arial, Helvetica">entry_declaration</FONT> denoted
by E. </DL>
<DIV Class="Paranum"><FONT SIZE=-2>15</FONT></DIV>
<DIV Class="Normal"> <A NAME="I6736"></A>Program_Error is raised if
a value of Null_Task_ID is passed as a parameter to Abort_Task, Is_Terminated,
and Is_Callable.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>16</FONT></DIV>
<DIV Class="Normal"> <A NAME="I6737"></A><A NAME="I6738"></A>Abort_Task
is a potentially blocking operation (see <A HREF="AA-9-5-1.html">9.5.1</A>).
</DIV>
<H4 ALIGN=CENTER>Bounded (Run-Time) Errors</H4>
<DIV Class="Paranum"><FONT SIZE=-2>17</FONT></DIV>
<DIV Class="Normal"> <A NAME="I6739"></A>It is a bounded error to
call the Current_Task function from an entry body or an interrupt handler.
<A NAME="I6740"></A>Program_Error is raised, or an implementation-defined
value of the type Task_ID is returned. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
value of Current_Task when in a protected entry or interrupt handler.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>17.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation Note: </B>This
value could be Null_Task_ID, or the ID of some user task, or that of
an internal task created by the implementation. </FONT></DIV>
<H4 ALIGN=CENTER>Erroneous Execution</H4>
<DIV Class="Paranum"><FONT SIZE=-2>18</FONT></DIV>
<DIV Class="Normal"> <A NAME="I6741"></A>If a value of Task_ID is
passed as a parameter to any of the operations declared in this package
(or any language-defined child of this package), and the corresponding
task object no longer exists, the execution of the program is erroneous.
</DIV>
<H4 ALIGN=CENTER>Documentation Requirements</H4>
<DIV Class="Paranum"><FONT SIZE=-2>19</FONT></DIV>
<DIV Class="Normal"> The implementation shall document the effect
of calling Current_Task from an entry body or interrupt handler. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>19.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
effect of calling Current_Task from an entry body or interrupt handler.</FONT></DIV>
<DIV Class="NotesHeader"><FONT SIZE=-1>NOTES</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>20</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>10 This package is intended
for use in writing user-defined task scheduling packages and constructing
server tasks. Current_Task can be used in conjunction with other operations
requiring a task as an argument such as Set_Priority (see <A HREF="AA-D-5.html">D.5</A>).</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>21</FONT></DIV>
<DIV Class="Notes"><FONT SIZE=-1>11 The function Current_Task
and the attribute Caller can return a Task_ID value that identifies the
environment task.</FONT></DIV>
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