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9.11 Example of Tasking and Synchronization
Examples
1
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:
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task Producer;
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task body Producer is
Char : Character;
begin
loop
... -- produce the next character Char
Buffer.Write(Char);
exit when Char = ASCII.EOT;
end loop;
end Producer;
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and the consuming
task might have the following structure:
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task Consumer;
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task body Consumer is
Char : Character;
begin
loop
Buffer.Read(Char);
exit when Char = ASCII.EOT;
... -- consume the character Char
end loop;
end Consumer;
7
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.
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protected Buffer is
entry Read (C : out Character);
entry Write(C : in Character);
private
Pool : String(1 .. 100);
Count : Natural := 0;
In_Index, Out_Index : Positive := 1;
end Buffer;
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protected body Buffer is
entry Write(C : in Character)
when Count < Pool'Length is
begin
Pool(In_Index) := C;
In_Index := (In_Index mod Pool'Length) + 1;
Count := Count + 1;
end Write;
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entry Read(C : out Character)
when Count > 0 is
begin
C := Pool(Out_Index);
Out_Index := (Out_Index mod Pool'Length) + 1;
Count := Count - 1;
end Read;
end Buffer;
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