[SAB] Test262 Agent harness

test/test262/harness-agent.js

Index: test/test262/harness-agent.js
diff --git a/test/test262/harness-agent.js b/test/test262/harness-agent.js
new file mode 100644
index 0000000000000000000000000000000000000000..4bf5df20774eb4e37858caba490cd1e43cdb66b2
--- /dev/null
+++ b/test/test262/harness-agent.js
@@ -0,0 +1,103 @@
+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+$.agent = (function () {
+
+var workers = [];
+var i32a = new Int32Array(new SharedArrayBuffer(256));

[Dan Ehrenberg, 2017/01/28 03:41:06]

Would it make sense to avoid creating this array until anyone calls start()?
Maybe that would minimize the performance regression in test262 (which is
already one of the longer-running test suites), especially if this harness file
is run for every single test, even those that don't use SharedArrayBuffer.

[binji, 2017/02/18 01:07:58]

Done.

+var pendingReports = [];
+
+// Agents call Atomics.wait on this location to sleep.
+var SLEEP_LOC = 0;
+// 1 if the started worker is ready, 0 otherwise.
+var START_LOC = 1;
+// The number of workers that have received the broadcast.
+var BROADCAST_LOC = 2;
+// Each worker has a count of outstanding reports; worker N uses memory
+// location [WORKER_REPORT_LOC + N].
+var WORKER_REPORT_LOC = 3;
+
+function workerScript(script) {
+  return `
+    var index;
+    var i32a = null;
+    var broadcasts = [];
+    var pendingReceiver = null;
+
+    function handleBroadcast() {
+      if (pendingReceiver && broadcasts.length > 0) {
+        pendingReceiver.apply(null, broadcasts.shift());
+        pendingReceiver = null;
+      }
+    };
+
+    var onmessage = function(msg) {
+      switch (msg.kind) {
+        case 'start':
+          i32a = msg.i32a;
+          index = msg.index;
+          ${script}

[Dan Ehrenberg, 2017/01/28 03:41:06]

Eh, to be pedantic, this doesn't really do exactly what the description says;
the "script" is not run in top-level script context. But maybe it's fine to wait
to fix this when someone checks in a test262 test that fails because of it;
plenty of other tests exist to test top-level script-ness, and I don't see why
you'd want to test that in conjunction with agents.

If you wanted to get a little closer without much work, you could do an indirect
eval here.

[binji, 2017/02/18 01:07:58]

Done.

+          break;
+
+        case 'broadcast':
+          Atomics.add(i32a, ${BROADCAST_LOC}, 1);
+          broadcasts.push([msg.sab, msg.id]);
+          handleBroadcast();
+          break;
+      }
+    };
+
+    var $ = {
+      agent: {
+        receiveBroadcast(receiver) {
+          pendingReceiver = receiver;
+          handleBroadcast();
+        },
+
+        report(msg) {
+          postMessage(msg);
+          Atomics.add(i32a, ${WORKER_REPORT_LOC} + index, 1);
+        },
+
+        sleep(s) { Atomics.wait(i32a, ${SLEEP_LOC}, 0, s); },
+
+        leaving() {}
+      }
+    };`;
+}
+
+var agent = {
+  start(script) {
+    var w = new Worker(workerScript(script));
+    w.index = workers.length;
+    w.postMessage({kind: 'start', i32a: i32a, index: w.index});
+    workers.push(w);
+  },
+
+  broadcast(sab, id) {
+    Atomics.store(i32a, BROADCAST_LOC, 0);
+
+    for (var w of workers) {
+      w.postMessage({kind: 'broadcast', sab: sab, id: id|0});
+    }
+
+    while (Atomics.load(i32a, BROADCAST_LOC) != workers.length) {}
+  },
+
+  getReport() {
+    for (var w of workers) {
+      while (Atomics.load(i32a, WORKER_REPORT_LOC + w.index) > 0) {
+        pendingReports.push(w.getMessage());
+        Atomics.sub(i32a, WORKER_REPORT_LOC + w.index, 1);
+      }
+    }
+
+    return pendingReports.shift() || null;
+  },
+
+  sleep(s) { Atomics.wait(i32a, SLEEP_LOC, 0, s); }
+};
+return agent;
+
+})();