michael@0: // |reftest| skip
michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: //-----------------------------------------------------------------------
michael@0: 
michael@0: var summary = "Lamport Bakery's algorithm for mutual exclusion";
michael@0: // Adapted from pseudocode in Wikipedia:
michael@0: // http://en.wikipedia.org/wiki/Lamport%27s_bakery_algorithm
michael@0: 
michael@0: printStatus(summary);
michael@0: 
michael@0: var N = 15; // Number of threads.
michael@0: var LOOP_COUNT = 10; // Number of times each thread should loop
michael@0: 
michael@0: function range(n) {
michael@0:   for (let i = 0; i < n; i++)
michael@0:     yield i;
michael@0: }
michael@0: 
michael@0: function max(a) {
michael@0:   let x = Number.NEGATIVE_INFINITY;
michael@0:   for each (let i in a)
michael@0:     if (i > x)
michael@0:       x = i;
michael@0:   return x;
michael@0: }
michael@0: 
michael@0: // the mutex mechanism
michael@0: var entering = [false for (i in range(N))];
michael@0: var ticket = [0 for (i in range(N))];
michael@0: 
michael@0: // the object being protected
michael@0: var counter = 0;
michael@0: 
michael@0: function lock(i)
michael@0: {
michael@0:   entering[i] = true;
michael@0:   ticket[i] = 1 + max(ticket);
michael@0:   entering[i] = false;
michael@0: 
michael@0:   for (let j = 0; j < N; j++) {
michael@0:     // If thread j is in the middle of getting a ticket, wait for that to
michael@0:     // finish.
michael@0:     while (entering[j])
michael@0:       ;
michael@0: 
michael@0:     // Wait until all threads with smaller ticket numbers or with the same
michael@0:     // ticket number, but with higher priority, finish their work.
michael@0:     while ((ticket[j] != 0) && ((ticket[j] < ticket[i]) ||
michael@0:                                 ((ticket[j] == ticket[i]) && (i < j))))
michael@0:       ;
michael@0:   }
michael@0: }
michael@0: 
michael@0: function unlock(i) {
michael@0:   ticket[i] = 0;
michael@0: }
michael@0: 
michael@0: function worker(i) {
michael@0:   for (let k = 0; k < LOOP_COUNT; k++) {
michael@0:     lock(i);
michael@0: 
michael@0:     // The critical section
michael@0:     let x = counter;
michael@0:     sleep(0.003);
michael@0:     counter = x + 1;
michael@0: 
michael@0:     unlock(i);
michael@0:   }
michael@0:   return 'ok';
michael@0: }
michael@0: 
michael@0: function makeWorker(id) {
michael@0:   return function () { return worker(id); };
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:   scatter([makeWorker(i) for (i in range(N))]);
michael@0: 
michael@0:   expect = "counter: " + (N * LOOP_COUNT);
michael@0:   actual = "counter: " + counter;
michael@0: }
michael@0: 
michael@0: reportCompare(expect, actual, summary);