Bug 1610682 - Time out of eager evaluation after 100ms. r=jlast

Differential Revision: https://phabricator.services.mozilla.com/D61775

--HG--
extra : moz-landing-system : lando

devtools/server/actors/webconsole/eval-with-debugger.js

@@ -275,11 +275,31 @@ function preventSideEffects(dbg) {
   // TODO: re-enable addAllGlobalsAsDebuggees(bug #1610532)
   // dbg.addAllGlobalsAsDebuggees();
 
+  const timeoutDuration = 100;
+  const endTime = Date.now() + timeoutDuration;
+  let count = 0;
+  function shouldCancel() {
+    // To keep the evaled code as quick as possible, we avoid querying the
+    // current time on ever single step and instead check every 100 steps
+    // as an arbitrary count that seemed to be "often enough".
+    return ++count % 100 === 0 && Date.now() > endTime;
+  }
+
   dbg.onEnterFrame = frame => {
+    if (shouldCancel()) {
+      return null;
+    }
+    frame.onStep = () => {
+      if (shouldCancel()) {
+        return null;
+      }
+      return undefined;
+    };
+
     const script = frame.script;
 
     if (data.executedScripts.has(script)) {
-      return;
+      return undefined;
     }
     data.executedScripts.add(script);
 
@@ -287,6 +307,8 @@ function preventSideEffects(dbg) {
     for (const offset of offsets) {
       script.setBreakpoint(offset, data.handler);
     }
+
+    return undefined;
   };
 
   dbg.onNativeCall = (callee, reason) => {

devtools/server/tests/xpcshell/test_console_eval-01.js

@@ -0,0 +1,34 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+/*
+ * Check that is possible to evaluate JS with evaluation timeouts in place.
+ */
+
+add_task(
+  threadFrontTest(async ({ threadFront, targetFront, debuggee }) => {
+    const consoleFront = await targetFront.getFront("console");
+    await consoleFront.evaluateJSAsync(`
+      function fib(n) {
+        if (n == 1 || n == 0) {
+          return 1;
+        }
+
+        return fib(n-1) + fib(n-2)
+      }
+    `);
+
+    const normalResult = await consoleFront.evaluateJSAsync("fib(1)", {
+      eager: true,
+    });
+    Assert.equal(normalResult.result, 1, "normal eval");
+
+    const timeoutResult = await consoleFront.evaluateJSAsync("fib(100)", {
+      eager: true,
+    });
+    Assert.equal(typeof timeoutResult.result, "object", "timeout eval");
+    Assert.equal(timeoutResult.result.type, "undefined", "timeout eval type");
+  })
+);

devtools/server/tests/xpcshell/xpcshell.ini

@@ -122,6 +122,7 @@ skip-if = true # breakpoint sliding is not supported bug 1525685
 [test_conditional_breakpoint-02.js]
 [test_conditional_breakpoint-03.js]
 [test_conditional_breakpoint-04.js]
+[test_console_eval-01.js]
 [test_logpoint-01.js]
 [test_logpoint-02.js]
 [test_logpoint-03.js]