Fix assertion starting cast_shell (breaking thread IO restrictions).

ui/events/ozone/device/device_manager_manual.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/ozone/device/device_manager_manual.h"
 
+#include "base/bind.h"
+#include "base/callback.h"
 #include "base/files/file_enumerator.h"
+#include "base/location.h"
+#include "base/threading/worker_pool.h"
 #include "ui/events/ozone/device/device_event.h"
 #include "ui/events/ozone/device/device_event_observer.h"
 
 namespace ui {
 
-DeviceManagerManual::DeviceManagerManual() {}
+namespace {
 
-DeviceManagerManual::~DeviceManagerManual() {}
-
-void DeviceManagerManual::ScanDevices(DeviceEventObserver* observer) {
+void ScanDevicesOnWorkerThread(std::vector<base::FilePath>* result) {
   base::FileEnumerator file_enum(base::FilePath("/dev/input"),
                                  false,
                                  base::FileEnumerator::FILES,
                                  "event*[0-9]");
   for (base::FilePath path = file_enum.Next(); !path.empty();
        path = file_enum.Next()) {
-    DeviceEvent event(DeviceEvent::INPUT, DeviceEvent::ADD, path);
-    observer->OnDeviceEvent(event);
+    result->push_back(path);
+  }
+}
+}
+
+DeviceManagerManual::DeviceManagerManual()
+    : have_scanned_devices_(false), weak_ptr_factory_(this) {
+}
+
+DeviceManagerManual::~DeviceManagerManual() {
+}
+
+void DeviceManagerManual::ScanDevices(DeviceEventObserver* observer) {
+  if (have_scanned_devices_) {

[dnicoara, 2015/01/22 22:38:57]

Drive-by comment: If multiple callers end up scanning before the worker task
returns, there will be multiple calls to OnDevicesScanned, right? You'll need to
diff between the stored list and the new list otherwise all the devices that
appear in both lists will be duplicates. (Or maybe just discard the old list.)

I wonder if it's worth dropping |have_scanned_devices_| and always posting the
call to ScanDevicesOnWorkerThread()?

[spang, 2015/01/22 22:42:02]

have_scanned_devices_ is set here in this function, not after the scan
completes. It is not possible to kick off a 2nd scan.

[dnicoara, 2015/01/22 22:43:13]

Oh, sorry, didn't notice it. Sorry for the noise.

+    std::vector<base::FilePath>::const_iterator it = devices_.begin();
+    for (; it != devices_.end(); ++it) {
+      DeviceEvent event(DeviceEvent::INPUT, DeviceEvent::ADD, *it);
+      observer->OnDeviceEvent(event);
+    }
+  } else {
+    std::vector<base::FilePath>* result = new std::vector<base::FilePath>();
+    base::WorkerPool::PostTaskAndReply(
+        FROM_HERE, base::Bind(&ScanDevicesOnWorkerThread, result),
+        base::Bind(&DeviceManagerManual::OnDevicesScanned,
+                   weak_ptr_factory_.GetWeakPtr(), base::Owned(result)),
+        false /* task_is_slow */);
+    have_scanned_devices_ = true;
   }
 }
 
-void DeviceManagerManual::AddObserver(DeviceEventObserver* observer) {}
+void DeviceManagerManual::AddObserver(DeviceEventObserver* observer) {
+  observers_.AddObserver(observer);
+}
 
-void DeviceManagerManual::RemoveObserver(DeviceEventObserver* observer) {}
+void DeviceManagerManual::RemoveObserver(DeviceEventObserver* observer) {
+  observers_.RemoveObserver(observer);
+}
+
+void DeviceManagerManual::OnDevicesScanned(
+    std::vector<base::FilePath>* result) {
+  std::vector<base::FilePath>::const_iterator it = result->begin();
+  for (; it != result->end(); ++it) {
+    devices_.push_back(*it);
+    DeviceEvent event(DeviceEvent::INPUT, DeviceEvent::ADD, *it);
+    FOR_EACH_OBSERVER(DeviceEventObserver, observers_, OnDeviceEvent(event));
+  }
+}
 
 }  // namespace ui