Support use of third party time function for about:profiler

This uses TCMalloc to provide a time function, allowing
us to see how much memory was allocated on a single thread
during the running of a task.  The alternate time function
is put in place only when a specific environment variable
is detected during TCMalloc startup.

This change currently is activated only in Windows/Linux,
as it is based on changes TCMalloc (not used on Mac).

We also create an infrastructure for using any alternate
timer, to replace the "wall clock time," on a per-thread
basis, in the about:profiler infrastructure.  That interface
may be used on other platforms, including scenarios where
we have a per-thread-CPU-time function to replace the
wall-clock timer.  In all cases, when this alternate timer
is activated, we lose the ability to calculated queueing
time.  Queueing time is based on a time snapshot taken on
a second thread, and hence is not comparable to the
alternate timer (when the alternate timer is engaged).


r=rtenneti
BUG=103321
Review URL: https://chromiumcodereview.appspot.com/9212025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@122180 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 63 insertions, 0 deletions

diff --git a/base/profiler/alternate_timer.cc b/base/profiler/alternate_timer.cc
new file mode 100644
index 0000000..05a983c
--- /dev/null
+++ b/base/profiler/alternate_timer.cc
@@ -0,0 +1,25 @@
+// Copyright (c) 2012 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/profiler/alternate_timer.h"
+
+#include "base/logging.h"
+
+namespace tracked_objects {
+
+static NowFunction* g_time_function = NULL;
+
+const char kAlternateProfilerTime[] = "CHROME_PROFILER_TIME";
+
+// Set an alternate timer function to replace the OS time function when
+// profiling.
+void SetAlternateTimeSource(NowFunction* now_function) {
+  DCHECK_EQ(g_time_function, reinterpret_cast<NowFunction*>(NULL));
+  g_time_function = now_function;
+}
+
+extern NowFunction* GetAlternateTimeSource() {
+  return g_time_function;
+}
+}  // tracked_objects
diff --git a/base/profiler/alternate_timer.h b/base/profiler/alternate_timer.h
new file mode 100644
index 0000000..883b24f
--- /dev/null
+++ b/base/profiler/alternate_timer.h
@@ -0,0 +1,36 @@
+// Copyright (c) 2012 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.
+
+// This is a glue file, which allows third party code to call into our profiler
+// without having to include most any functions from base.
+
+
+#ifndef BASE_PROFILER_ALTERNATE_TIMER_H_
+#define BASE_PROFILER_ALTERNATE_TIMER_H_
+
+namespace tracked_objects {
+
+// Provide type for an alternate timer function.
+typedef unsigned int NowFunction();
+
+// Set an alternate timer function to replace the OS time function when
+// profiling.  Typically this is called by an allocator that is providing a
+// function that indicates how much memory has been allocated on any given
+// thread.
+extern void SetAlternateTimeSource(NowFunction* now_function);
+
+// Gets the pointer to a function that was set via SetAlternateTimeSource().
+// Returns NULL if no set was done prior to calling GetAlternateTimeSource.
+extern NowFunction* GetAlternateTimeSource();
+
+// Environment variable name that is used to activate alternate timer profiling
+// (such as using TCMalloc allocations to provide a pseudo-timer) for tasks
+// instead of wall clock profiling.
+extern const char kAlternateProfilerTime[];
+
+
+
+}  // tracked_objects
+
+#endif  // BASE_PROFILER_ALTERNATE_TIMER_H_
diff --git a/base/profiler/tracked_time.h b/base/profiler/tracked_time.h
index 6f4bc7e..5493e20 100644
--- a/base/profiler/tracked_time.h
+++ b/base/profiler/tracked_time.h
@@ -62,6 +62,8 @@ class BASE_EXPORT TrackedTime {  // Similar to base::TimeTicks.
   TrackedTime operator+(const Duration& other) const;
   bool is_null() const;
 
+  static TrackedTime FromMilliseconds(int32 ms) { return TrackedTime(ms); }
+
  private:
   friend class Duration;
   explicit TrackedTime(int32 ms);