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<H1> 9.11 Example of Tasking and Synchronization</H1>
<H4 ALIGN=CENTER>Examples</H4>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The following example
defines a buffer protected object to smooth variations between the speed
of output of a producing task and the speed of input of some consuming
task. For instance, the producing task might have the following structure:</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Examples"><TT><B>task</B> Producer;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Examples"><TT><B>task body</B> Producer <B>is</B><BR>
Char : Character;<BR>
<B>begin</B><BR>
<B>loop</B><BR>
... <I>-- produce the next character Char</I><BR>
Buffer.Write(Char);<BR>
<B>exit</B> <B>when</B> Char = ASCII.EOT;<BR>
<B>end</B> <B>loop</B>;<BR>
<B>end</B> Producer;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> and the consuming
task might have the following structure:</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>5</FONT></DIV>
<DIV Class="Examples"><TT><B>task</B> Consumer;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>6</FONT></DIV>
<DIV Class="Examples" Style="margin-bottom: 0.9em"><TT><B>task body</B> Consumer <B>is</B><BR>
Char : Character;<BR>
<B>begin</B><BR>
<B>loop</B><BR>
Buffer.Read(Char);<BR>
<B>exit</B> <B>when</B> Char = ASCII.EOT;<BR>
... <I>-- consume the character Char</I><BR>
<B>end</B> <B>loop</B>;<BR>
<B>end</B> Consumer;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>7</FONT></DIV>
<DIV Class="Normal" Style="margin-bottom: 0.4em"> The buffer object
contains an internal pool of characters managed in a round-robin fashion.
The pool has two indices, an In_Index denoting the space for the next
input character and an Out_Index denoting the space for the next output
character.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>8</FONT></DIV>
<DIV Class="Examples"><TT><B>protected</B> Buffer <B>is</B><BR>
<B>entry</B> Read (C : <B>out</B> Character);<BR>
<B>entry</B> Write(C : <B>in</B> Character);<BR>
<B>private</B><BR>
Pool : String(1 .. 100);<BR>
Count : Natural := 0;<BR>
In_Index, Out_Index : Positive := 1;<BR>
<B>end</B> Buffer;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>9</FONT></DIV>
<DIV Class="Examples"><TT><B>protected body</B> Buffer <B>is</B><BR>
<B>entry</B> Write(C : <B>in</B> Character)<BR>
<B>when</B> Count < Pool'Length <B>is</B><BR>
<B>begin</B><BR>
Pool(In_Index) := C;<BR>
In_Index := (In_Index <B>mod</B> Pool'Length) + 1;<BR>
Count := Count + 1;<BR>
<B>end</B> Write;</TT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>10</FONT></DIV>
<DIV Class="Examples"><TT> <B>entry</B> Read(C : <B>out</B> Character)<BR>
<B>when</B> Count > 0 <B>is</B><BR>
<B>begin</B><BR>
C := Pool(Out_Index);<BR>
Out_Index := (Out_Index <B>mod</B> Pool'Length) + 1;<BR>
Count := Count - 1;<BR>
<B>end</B> Read;<BR>
<B>end</B> Buffer;</TT></DIV>
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