8 files changed, 360 insertions, 0 deletions
diff --git a/devtools/platform/components.conf b/devtools/platform/components.conf
new file mode 100644
index 0000000000..7e7d451b83
--- /dev/null
+++ b/devtools/platform/components.conf
@@ -0,0 +1,14 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+Classes = [
+    {
+        'cid': '{ec5aa99c-7abb-4142-ac5f-aab2419e38e2}',
+        'contract_ids': ['@mozilla.org/jsinspector;1'],
+        'type': 'mozilla::jsinspector::nsJSInspector',
+        'headers': ['/devtools/platform/nsJSInspector.h'],
+    },
+]
diff --git a/devtools/platform/moz.build b/devtools/platform/moz.build
new file mode 100644
index 0000000000..2a2cba6f0a
--- /dev/null
+++ b/devtools/platform/moz.build
@@ -0,0 +1,23 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+XPCSHELL_TESTS_MANIFESTS += ["tests/xpcshell/xpcshell.ini"]
+
+XPIDL_SOURCES += [
+    "nsIJSInspector.idl",
+]
+
+XPIDL_MODULE = "jsinspector"
+
+SOURCES += [
+    "nsJSInspector.cpp",
+]
+
+XPCOM_MANIFESTS += [
+    "components.conf",
+]
+
+FINAL_LIBRARY = "xul"
diff --git a/devtools/platform/nsIJSInspector.idl b/devtools/platform/nsIJSInspector.idl
new file mode 100644
index 0000000000..40ad495234
--- /dev/null
+++ b/devtools/platform/nsIJSInspector.idl
@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+/**
+ * Utilities for running nested event loops, asking them to return, and
+ * keeping track of which ones are still running.
+ */
+[scriptable, uuid(6758d0d7-e96a-4c5c-bca8-3bcbe5a15943)]
+interface nsIJSInspector : nsISupports
+{
+  /**
+   * Process the current thread's event queue, calling event handlers until
+   * a call to exitNestedEventLoop, below, asks us to return.
+   *
+   * The name 'enterNestedEventLoop' may be misleading if read too literally.
+   * This method loops calling event handlers until one asks it to stop, and
+   * then returns. So by that point, the nested event loop has been not only
+   * entered, but also run and exited.
+   *
+   * When enterNestedEventLoop calls an event handler, that handler may itself
+   * call enterNestedEventLoop, and so on, so that there may be arbitrarily
+   * many such calls on the stack at the same time.
+   *
+   * We say an enterNestedEventLoop call is "running" if it has not yet been
+   * asked to return, or "stopped" if it has been asked to return once it has
+   * finished processing the current event.
+   *
+   * @param requestor   A token of the caller's choice to identify this event
+   *                    loop.
+   *
+   * @return depth      The number of running enterNestedEventLoop calls
+   *                    remaining, now that this one has returned.
+   *
+   *                    (Note that not all calls still on the stack are
+   *                    necessary running; exitNestedEventLoop can ask any
+   *                    number of enterNestedEventLoop calls to return.)
+   */
+  unsigned long enterNestedEventLoop(in jsval requestor);
+
+  /**
+   * Stop the youngest running enterNestedEventLoop call, asking it to return
+   * once it has finished processing the current event.
+   *
+   * The name 'exitNestedEventLoop' may be misleading if read too literally.
+   * The affected event loop does not return immediately when this method is
+   * called. Rather, this method simply returns to its caller; the affected
+   * loop's current event handler is allowed to run to completion; and then
+   * that loop returns without processing any more events.
+   *
+   * This method ignores loops that have already been stopped, and operates on
+   * the youngest loop that is still running. Each call to this method stops
+   * another running loop.
+   *
+   * @return depth      The number of running enterNestedEventLoop calls
+   *                    remaining, now that one has been stopped.
+   *
+   * @throws NS_ERROR_FAILURE if there are no running enterNestedEventLoop calls.
+   */
+  unsigned long exitNestedEventLoop();
+
+  /**
+    * The number of running enterNestedEventLoop calls on the stack.
+    * This count does not include stopped enterNestedEventLoop calls.
+    */
+  readonly attribute unsigned long eventLoopNestLevel;
+
+  /**
+   * The |requestor| value that was passed to the youngest running
+   * enterNestedEventLoop call.
+   */
+  readonly attribute jsval lastNestRequestor;
+};
diff --git a/devtools/platform/nsJSInspector.cpp b/devtools/platform/nsJSInspector.cpp
new file mode 100644
index 0000000000..02822fb568
--- /dev/null
+++ b/devtools/platform/nsJSInspector.cpp
@@ -0,0 +1,119 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsJSInspector.h"
+#include "jsfriendapi.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/SpinEventLoopUntil.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsServiceManagerUtils.h"
+#include "nsMemory.h"
+#include "nsArray.h"
+#include "nsTArray.h"
+
+#define JSINSPECTOR_CONTRACTID "@mozilla.org/jsinspector;1"
+
+#define JSINSPECTOR_CID                              \
+  {                                                  \
+    0xec5aa99c, 0x7abb, 0x4142, {                    \
+      0xac, 0x5f, 0xaa, 0xb2, 0x41, 0x9e, 0x38, 0xe2 \
+    }                                                \
+  }
+
+namespace mozilla {
+namespace jsinspector {
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsJSInspector)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+  NS_INTERFACE_MAP_ENTRY(nsIJSInspector)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsJSInspector)
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(nsJSInspector)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(nsJSInspector)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsJSInspector)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsJSInspector)
+  tmp->mRequestors.Clear();
+  tmp->mLastRequestor = JS::NullValue();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsJSInspector)
+  for (uint32_t i = 0; i < tmp->mRequestors.Length(); ++i) {
+    NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mRequestors[i])
+  }
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mLastRequestor)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+nsJSInspector::nsJSInspector()
+    : mNestedLoopLevel(0), mRequestors(1), mLastRequestor(JS::NullValue()) {}
+
+nsJSInspector::~nsJSInspector() {
+  MOZ_ASSERT(mRequestors.Length() == 0);
+  MOZ_ASSERT(mLastRequestor.isNull());
+  mozilla::DropJSObjects(this);
+}
+
+NS_IMETHODIMP
+nsJSInspector::EnterNestedEventLoop(JS::Handle<JS::Value> requestor,
+                                    uint32_t* out) {
+  nsresult rv = NS_OK;
+
+  mLastRequestor = requestor;
+  mRequestors.AppendElement(requestor);
+  mozilla::HoldJSObjects(this);
+
+  mozilla::dom::AutoNoJSAPI nojsapi;
+
+  uint32_t nestLevel = ++mNestedLoopLevel;
+  if (!SpinEventLoopUntil([&]() { return mNestedLoopLevel < nestLevel; })) {
+    rv = NS_ERROR_UNEXPECTED;
+  }
+
+  NS_ASSERTION(mNestedLoopLevel <= nestLevel,
+               "nested event didn't unwind properly");
+
+  if (mNestedLoopLevel == nestLevel) {
+    mLastRequestor = mRequestors.ElementAt(--mNestedLoopLevel);
+  }
+
+  *out = mNestedLoopLevel;
+  return rv;
+}
+
+NS_IMETHODIMP
+nsJSInspector::ExitNestedEventLoop(uint32_t* out) {
+  if (mNestedLoopLevel > 0) {
+    mRequestors.RemoveElementAt(--mNestedLoopLevel);
+    if (mNestedLoopLevel > 0)
+      mLastRequestor = mRequestors.ElementAt(mNestedLoopLevel - 1);
+    else
+      mLastRequestor = JS::NullValue();
+  } else {
+    return NS_ERROR_FAILURE;
+  }
+
+  *out = mNestedLoopLevel;
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsJSInspector::GetEventLoopNestLevel(uint32_t* out) {
+  *out = mNestedLoopLevel;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsJSInspector::GetLastNestRequestor(JS::MutableHandle<JS::Value> out) {
+  out.set(mLastRequestor);
+  return NS_OK;
+}
+
+}  // namespace jsinspector
+}  // namespace mozilla
diff --git a/devtools/platform/nsJSInspector.h b/devtools/platform/nsJSInspector.h
new file mode 100644
index 0000000000..61cc864976
--- /dev/null
+++ b/devtools/platform/nsJSInspector.h
@@ -0,0 +1,38 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2; -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef COMPONENTS_JSINSPECTOR_H
+#define COMPONENTS_JSINSPECTOR_H
+
+#include "nsIJSInspector.h"
+#include "mozilla/Attributes.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsTArray.h"
+#include "js/Value.h"
+#include "js/RootingAPI.h"
+
+namespace mozilla {
+namespace jsinspector {
+
+class nsJSInspector final : public nsIJSInspector {
+ public:
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(nsJSInspector)
+  NS_DECL_NSIJSINSPECTOR
+
+  nsJSInspector();
+
+ private:
+  ~nsJSInspector();
+
+  uint32_t mNestedLoopLevel;
+  nsTArray<JS::Heap<JS::Value> > mRequestors;
+  JS::Heap<JS::Value> mLastRequestor;
+};
+
+}  // namespace jsinspector
+}  // namespace mozilla
+
+#endif
diff --git a/devtools/platform/tests/xpcshell/.eslintrc.js b/devtools/platform/tests/xpcshell/.eslintrc.js
new file mode 100644
index 0000000000..dc7f2c85c4
--- /dev/null
+++ b/devtools/platform/tests/xpcshell/.eslintrc.js
@@ -0,0 +1,19 @@
+"use strict";
+
+// Parent config file for all devtools xpcshell files.
+module.exports = {
+  extends: ["plugin:mozilla/xpcshell-test"],
+  rules: {
+    // Allow non-camelcase so that run_test doesn't produce a warning.
+    camelcase: "off",
+    // Allow using undefined variables so that tests can refer to functions
+    // and variables defined in head.js files, without having to maintain a
+    // list of globals in each .eslintrc file.
+    // Note that bug 1168340 will eventually help auto-registering globals
+    // from head.js files.
+    "no-undef": "off",
+    "block-scoped-var": "off",
+    // Tests can always import anything.
+    "mozilla/reject-some-requires": "off",
+  },
+};
diff --git a/devtools/platform/tests/xpcshell/test_nsjsinspector.js b/devtools/platform/tests/xpcshell/test_nsjsinspector.js
new file mode 100644
index 0000000000..a5e63c0cdf
--- /dev/null
+++ b/devtools/platform/tests/xpcshell/test_nsjsinspector.js
@@ -0,0 +1,66 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test the basic functionality of the nsIJSInspector component.
+var gCount = 0;
+const MAX = 10;
+
+const { Services } = ChromeUtils.import("resource://gre/modules/Services.jsm");
+var inspector = Cc["@mozilla.org/jsinspector;1"].getService(Ci.nsIJSInspector);
+
+// Emulate 10 simultaneously-debugged windows from 3 separate client connections.
+var requestor = count => ({
+  url: "http://foo/bar/" + count,
+  connection: "conn" + (count % 3),
+});
+
+function run_test() {
+  test_nesting();
+}
+
+function test_nesting() {
+  Assert.equal(inspector.eventLoopNestLevel, 0);
+
+  Services.tm.dispatchToMainThread({ run: enterEventLoop });
+
+  Assert.equal(inspector.enterNestedEventLoop(requestor(gCount)), 0);
+  Assert.equal(inspector.eventLoopNestLevel, 0);
+  Assert.equal(inspector.lastNestRequestor, null);
+}
+
+function enterEventLoop() {
+  if (gCount++ < MAX) {
+    Services.tm.dispatchToMainThread({ run: enterEventLoop });
+
+    Object.create(requestor(gCount));
+
+    Assert.equal(inspector.eventLoopNestLevel, gCount);
+    Assert.equal(inspector.lastNestRequestor.url, requestor(gCount - 1).url);
+    Assert.equal(
+      inspector.lastNestRequestor.connection,
+      requestor(gCount - 1).connection
+    );
+    Assert.equal(inspector.enterNestedEventLoop(requestor(gCount)), gCount);
+  } else {
+    Assert.equal(gCount, MAX + 1);
+    Services.tm.dispatchToMainThread({ run: exitEventLoop });
+  }
+}
+
+function exitEventLoop() {
+  if (inspector.lastNestRequestor != null) {
+    Assert.equal(inspector.lastNestRequestor.url, requestor(gCount - 1).url);
+    Assert.equal(
+      inspector.lastNestRequestor.connection,
+      requestor(gCount - 1).connection
+    );
+    if (gCount-- > 1) {
+      Services.tm.dispatchToMainThread({ run: exitEventLoop });
+    }
+
+    Assert.equal(inspector.exitNestedEventLoop(), gCount);
+    Assert.equal(inspector.eventLoopNestLevel, gCount);
+  }
+}
diff --git a/devtools/platform/tests/xpcshell/xpcshell.ini b/devtools/platform/tests/xpcshell/xpcshell.ini
new file mode 100644
index 0000000000..91430971a7
--- /dev/null
+++ b/devtools/platform/tests/xpcshell/xpcshell.ini
@@ -0,0 +1,6 @@
+[DEFAULT]
+tags = devtools
+firefox-appdir = browser
+skip-if = toolkit == 'android'
+
+[test_nsjsinspector.js]