Use TaskScheduler instead of WorkerPool in debug_daemon_client.cc.

chromeos/dbus/debug_daemon_client.cc

Index: chromeos/dbus/debug_daemon_client.cc
diff --git a/chromeos/dbus/debug_daemon_client.cc b/chromeos/dbus/debug_daemon_client.cc
index eda3a100ede97314e16a0d77c11ca75f9b47999b..9ec3104879f412e546d1b5aa23950fcee9be98ac 100644
--- a/chromeos/dbus/debug_daemon_client.cc
+++ b/chromeos/dbus/debug_daemon_client.cc
@@ -22,9 +22,8 @@
 #include "base/message_loop/message_loop.h"
 #include "base/posix/eintr_wrapper.h"
 #include "base/strings/string_util.h"
-#include "base/task_runner_util.h"
+#include "base/task_scheduler/post_task.h"
 #include "base/threading/thread_task_runner_handle.h"
-#include "base/threading/worker_pool.h"
 #include "chromeos/dbus/pipe_reader.h"
 #include "dbus/bus.h"
 #include "dbus/message.h"
@@ -55,9 +54,9 @@ void EmptyStopAgentTracingCallbackBody(
 class PipeReaderWrapper : public base::SupportsWeakPtr<PipeReaderWrapper> {
  public:
   explicit PipeReaderWrapper(const DebugDaemonClient::GetLogsCallback& callback)
-      : task_runner_(
-            base::WorkerPool::GetTaskRunner(true /** tasks_are_slow */)),
-        pipe_reader_(task_runner_,
+      : pipe_reader_(base::CreateTaskRunnerWithTraits(
+                         base::TaskTraits().WithFileIO().WithShutdownBehavior(

[hashimoto, 2016/12/09 10:54:37]

This task runner is used not to read a file, but to read a pipe which may wait
for the debug daemon on the other end of the pipe.

Which suits better for this use case, WithFileIO or WithWait?

[fdoray, 2016/12/09 16:49:14]

The WithFileIO() trait is appropriate for tasks that wait on synchronous file
I/O (file = file on disk, pipe, network socket...). I will improve the comment
in task_traits.h in a separate CL.

[hashimoto, 2016/12/10 01:13:55]

Thanks, improved comments would be appreciated.

Even if read() is the syscall used to interact with the file descriptor, pipe IO
doesn't wait for the disk to complete IO, but waits for another process to feed
data.
So IMHO WithWait() suits slightly better in this case, but if WithFileIO is
preferred and it's going to be clearly written in task_traits.h, I'll be OK with
it.

+                             base::TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN)),

[hashimoto, 2016/12/09 10:54:37]

PipeReader uses the task runner to provide it to net::FileStream.
Is net::FileStream safe to use with a task runner whose shutdown behavior is
CONTINUE_ON_SHUTDOWN?

[fdoray, 2016/12/09 16:49:14]

WorkerPool tasks are handled the same way as TaskScheduler CONTINUE_ON_SHUTDOWN
tasks on shutdown. Since the task ran in WorkerPool before this CL, it shouldn't
be a problem to run it in TaskScheduler with CONTINUE_ON_SHUTDOWN.

                      base::Bind(&PipeReaderWrapper::OnIOComplete, AsWeakPtr())),
         callback_(callback) {}