js/tests/js1_8/extensions/lamport.js

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  15  * The Original Code is JavaScript Engine testing utilities.
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  22  * Contributor(s): Guoxin Fan <gfan@sta.samsung.com>
  23  *                 Jason Orendorff <jorendorff@mozilla.com>
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  38
  39 var gTestfile = 'lamport.js'
  40 //-----------------------------------------------------------------------
  41
  42 var summary = "Lamport Bakery's algorithm for mutual exclusion";
  43 // Adapted from pseudocode in Wikipedia:
  44 // http://en.wikipedia.org/wiki/Lamport%27s_bakery_algorithm
  45
  46 printStatus(summary);
  47
  48 var N = 15; // Number of threads.
  49 var LOOP_COUNT = 10; // Number of times each thread should loop
  50
  51 function range(n) {
  52   for (let i = 0; i < n; i++)
  53     yield i;
  54 }
  55
  56 function max(a) {
  57   let x = Number.NEGATIVE_INFINITY;
  58   for each (let i in a)
  59     if (i > x)
  60       x = i;
  61   return x;
  62 }
  63
  64 // the mutex mechanism
  65 var entering = [false for (i in range(N))];
  66 var ticket = [0 for (i in range(N))];
  67
  68 // the object being protected
  69 var counter = 0;
  70
  71 function lock(i)
  72 {
  73   entering[i] = true;
  74   ticket[i] = 1 + max(ticket);
  75   entering[i] = false;
  76
  77   for (let j = 0; j < N; j++) {
  78     // If thread j is in the middle of getting a ticket, wait for that to
  79     // finish.
  80     while (entering[j])
  81       ;
  82
  83     // Wait until all threads with smaller ticket numbers or with the same
  84     // ticket number, but with higher priority, finish their work.
  85     while ((ticket[j] != 0) && ((ticket[j] < ticket[i]) ||
  86                                 ((ticket[j] == ticket[i]) && (i < j))))
  87       ;
  88   }
  89 }
  90
  91 function unlock(i) {
  92   ticket[i] = 0;
  93 }
  94
  95 function worker(i) {
  96   for (let k = 0; k < LOOP_COUNT; k++) {
  97     lock(i);
  98
  99     // The critical section
 100     let x = counter;
 101     sleep(0.003);
 102     counter = x + 1;
 103
 104     unlock(i);
 105   }
 106   return 'ok';
 107 }
 108
 109 function makeWorker(id) {
 110   return function () { return worker(id); };
 111 }
 112
 113 var expect;
 114 var actual;
 115
 116 if (typeof scatter == 'undefined' || typeof sleep == 'undefined') {
 117   print('Test skipped. scatter or sleep not defined.');
 118   expect = actual = 'Test skipped.';
 119 } else {
 120   scatter([makeWorker(i) for (i in range(N))]);
 121
 122   expect = "counter: " + (N * LOOP_COUNT);
 123   actual = "counter: " + counter;
 124 }
 125
 126 reportCompare(expect, actual, summary);