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POIssues in Ada Concurrency
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copied!<p>I need some help and also some insight. This is a program in Ada-2005 which has 3 tasks. The output is 'z'. If the 3 tasks do not happen in the order of their placement in the program then output can vary from z = 2, z = 1 to z = 0 ( That is easy to see in the program, mutual exclusion is attempted to make sure output is z = 2).</p> <pre><code>WITH Ada.Text_IO; USE Ada.Text_IO; WITH Ada.Integer_Text_IO; USE Ada.Integer_Text_IO; WITH System; USE System; procedure xyz is x : Integer := 0; y : Integer := 0; z : Integer := 0; task task1 is pragma Priority(System.Default_Priority + 3); end task1; task task2 is pragma Priority(System.Default_Priority + 2); end task2; task task3 is pragma Priority(System.Default_Priority + 1); end task3; task body task1 is begin x := x + 1; end task1; task body task2 is begin y := x + y; end task2; task body task3 is begin z := x + y + z; end task3; begin Put(" z = "); Put(z); end xyz; </code></pre> <p>I first tried this program </p> <p>(a) without pragmas, the result : In 100 tries, occurence of 2: 86, occurence of 1: 10, occurence of 0: 4.</p> <p>Then </p> <p>(b) with pragmas, the result : In 100 tries, occurence of 2: 84, occurence of 1 : 14, occurence of 0: 2.</p> <p>Which is unexpected as the 2 results are nearly identical. Which means pragmas or no pragmas the output has same behavior. </p> <p>Those who are Ada concurrency Gurus please shed some light on this topic. Alternative solutions with semaphores (if possible) is also invited.</p> <p>Further in my opinion for a critical process (that is what we do with Ada), with pragmas the result should be z = 2, 100% at all times, hence or otherwise this program should be termed as 85% critical !!!! (That should not be so with Ada)</p>

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