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copied!<p>A protected object to do the three operations might look something like this. But note, all this does is make sure that the three variables x, y and z are consistent with the order that the updates occurred in; it says nothing about the order.</p> <pre><code> protected P is procedure Update_X; procedure Update_Y; procedure Update_Z; function Get_Z return Integer; private X : Integer := 0; Y : Integer := 0; Z : Integer := 0; end P; protected body P is procedure Update_X is begin X := X + 1; end Update_X; procedure Update_Y is begin Y := Y + X; end Update_Y; procedure Update_Z is begin Z := X + Y + Z; end Update_Z; function Get_Z return Integer is begin return Z; end Get_Z; end P; </code></pre> <p>On the other hand, to make sure that the three tasks "submit their results" in the proper order, you could rewrite P so that a call to say Update_Y will block until Update_X has been called: Get_Z now has to be an entry with an out parameter rather than a function.</p> <pre><code> protected P is entry Update_X; entry Update_Y; entry Update_Z; entry Get_Z (Result : out Integer); private X_Updated : Boolean := False; Y_Updated : Boolean := False; Z_Updated : Boolean := False; X : Integer := 0; Y : Integer := 0; Z : Integer := 0; end P; protected body P is entry Update_X when True is begin X := X + 1; X_Updated := True; end Update_X; entry Update_Y when X_Updated is begin Y := Y + X; Y_Updated := True; end Update_Y; entry Update_Z when Y_Updated is begin Z := X + Y + Z; Z_Updated := True; end Update_Z; entry Get_Z (Result : out Integer) when Z_Updated is begin Result := Z; end Get_Z; end P; </code></pre> <p>The three tasks can now have any priority you like. But the task that calls Update_Z will block until the other two have reported.</p>

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