michael@0: // |reftest| skip
michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /*
michael@0:  * Any copyright is dedicated to the Public Domain.
michael@0:  * http://creativecommons.org/licenses/publicdomain/
michael@0:  * Contributor: Jason Orendorff
michael@0:  */
michael@0: 
michael@0: //-----------------------------------------------------------------------------
michael@0: 
michael@0: var summary = "Dekker's algorithm for mutual exclusion";
michael@0: // Adapted from pseudocode in Wikipedia:
michael@0: // http://en.wikipedia.org/wiki/Dekker%27s_algorithm
michael@0: 
michael@0: printStatus (summary);
michael@0: 
michael@0: var N = 500;  // number of iterations
michael@0: 
michael@0: // the mutex mechanism
michael@0: var f = [false, false];
michael@0: var turn = 0;
michael@0: 
michael@0: // resource being protected
michael@0: var counter = 0;
michael@0: 
michael@0: function worker(me) {
michael@0:   let him = 1 - me;
michael@0: 
michael@0:   for (let i = 0; i < N; i++) {
michael@0:     // enter the mutex
michael@0:     f[me] = true;
michael@0:     while (f[him]) {
michael@0:       if (turn != me) {
michael@0:         f[me] = false;
michael@0:         while (turn != me)
michael@0:           ;  // busy wait
michael@0:         f[me] = true;
michael@0:       }
michael@0:     }
michael@0: 
michael@0:     // critical section
michael@0:     let x = counter;
michael@0:     sleep(0.003);
michael@0:     counter = x + 1;
michael@0: 
michael@0:     // leave the mutex
michael@0:     turn = him;
michael@0:     f[me] = false;
michael@0:   }
michael@0: 
michael@0:   return 'ok';
michael@0: }
michael@0: 
michael@0: var expect;
michael@0: var actual;
michael@0: 
michael@0: if (typeof scatter == 'undefined' || typeof sleep == 'undefined') {
michael@0:   print('Test skipped. scatter or sleep not defined.');
michael@0:   expect = actual = 'Test skipped.';
michael@0: } else {
michael@0:   var results = scatter([function () { return worker(0); },
michael@0:                          function () { return worker(1); }]);
michael@0: 
michael@0:   expect = "Thread status: [ok,ok], counter: " + (2 * N);
michael@0:   actual = "Thread status: [" + results + "], counter: " + counter;
michael@0: }
michael@0: 
michael@0: reportCompare(expect, actual, summary);