Add CurrentProcessInfo::CreationTime() for Linux

base/process/process_info_linux.cc

+// Copyright 2013 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 "base/process/process_info.h"
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "base/process/internal_linux.h"
+#include "base/process/process_handle.h"
+#include "base/time/time.h"
+
+namespace base {
+namespace {
+
+using base::Time;
+
+Time* ProcessCreationTimeInternal() {
+  ProcessHandle pid = GetCurrentProcessHandle();
+  int start_ticks = internal::ReadProcStatsAndGetFieldAsInt(
+      pid, internal::VM_STARTTIME);
+  DCHECK(start_ticks);
+  TimeDelta start_offset = internal::ClockTicksToTimeDelta(start_ticks);
+  Time boot_time = internal::GetBootTime();
+  DCHECK(!boot_time.is_null());
+  return new Time(boot_time + start_offset);
+}
+
+}  // namespace
+
+//static
+const Time* CurrentProcessInfo::CreationTime() {
+  static Time* process_creation_time = ProcessCreationTimeInternal();

[jln (very slow on Chromium), 2013/08/06 18:57:29]

This caching seems a bit dangerous on Linux.

We use fork() extensively (see the Zygote) and this would give you the wrong
process creation time.

Could you bind process_creation_time to the current pid (and DCHECK this?). And
explain in the API that this won't work for forked processes?

Also how come you're not using a lock for process_creation_time ?

Thinking about these two pitfalls, I wonder if it wouldn't be better to not
cache this value in this API and let the caller do the caching as appropriate?

[James Simonsen, 2013/08/06 19:09:08]

I'll just remove it. It's done this way because that's how it's done on the
other OSes. They're all messed up in the same way. Will asked the same question
earlier.

+  return process_creation_time;
+}
+
+}  // namespace base