Simple Cache: set variable index flush delays

The flush delay is pulled from the experiment. The experiment group encodes two
values in the name separated by underscore. For example, experiment group
"5000_100" would set foreground flush interval to 5 seconds and background
interval to 100ms. I don't like commas in the name.

BUG=250796

Review URL: https://chromiumcodereview.appspot.com/17076006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@207087 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 32 insertions, 5 deletions

diff --git a/net/disk_cache/simple/simple_index.cc b/net/disk_cache/simple/simple_index.cc
index 56b9c01..8d65cbc 100644
--- a/net/disk_cache/simple/simple_index.cc
+++ b/net/disk_cache/simple/simple_index.cc
@@ -12,8 +12,11 @@
 #include "base/files/file_enumerator.h"
 #include "base/logging.h"
 #include "base/message_loop.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/pickle.h"
+#include "base/strings/string_number_conversions.h"
+#include "base/strings/string_tokenizer.h"
 #include "base/task_runner.h"
 #include "base/threading/worker_pool.h"
 #include "base/time.h"
@@ -30,10 +33,10 @@
 
 namespace {
 
-// How many seconds we delay writing the index to disk since the last cache
+// How many milliseconds we delay writing the index to disk since the last cache
 // operation has happened.
-const int kWriteToDiskDelayMSecs = 20000;
-const int kWriteToDiskOnBackgroundDelayMSecs = 100;
+const int kDefaultWriteToDiskDelayMSecs = 20000;
+const int kDefaultWriteToDiskOnBackgroundDelayMSecs = 100;
 
 // Divides the cache space into this amount of parts to evict when only one part
 // is left.
@@ -124,6 +127,24 @@ SimpleIndex::~SimpleIndex() {
 void SimpleIndex::Initialize() {
   DCHECK(io_thread_checker_.CalledOnValidThread());
 
+  // Take the foreground and background index flush delays from the experiment
+  // settings only if both are valid.
+  foreground_flush_delay_ = kDefaultWriteToDiskDelayMSecs;
+  background_flush_delay_ = kDefaultWriteToDiskOnBackgroundDelayMSecs;
+  const std::string index_flush_intervals = base::FieldTrialList::FindFullName(
+      "SimpleCacheIndexFlushDelay_Foreground_Background");
+  if (!index_flush_intervals.empty()) {
+    base::StringTokenizer tokens(index_flush_intervals, "_");
+    int foreground_delay, background_delay;
+    if (tokens.GetNext() &&
+        base::StringToInt(tokens.token(), &foreground_delay) &&
+        tokens.GetNext() &&
+        base::StringToInt(tokens.token(), &background_delay)) {
+      foreground_flush_delay_ = foreground_delay;
+      background_flush_delay_ = background_delay;
+    }
+  }
+
 #if defined(OS_ANDROID)
   activity_status_listener_.reset(new base::android::ActivityStatus::Listener(
       base::Bind(&SimpleIndex::OnActivityStateChange, AsWeakPtr())));
@@ -310,8 +331,8 @@ void SimpleIndex::InsertInEntrySet(
 void SimpleIndex::PostponeWritingToDisk() {
   if (!initialized_)
     return;
-  const int delay = app_on_background_ ? kWriteToDiskOnBackgroundDelayMSecs
-                                       : kWriteToDiskDelayMSecs;
+  const int delay = app_on_background_ ? background_flush_delay_
+                                       : foreground_flush_delay_;
   // If the timer is already active, Start() will just Reset it, postponing it.
   write_to_disk_timer_.Start(
       FROM_HERE, base::TimeDelta::FromMilliseconds(delay), write_to_disk_cb_);
diff --git a/net/disk_cache/simple/simple_index.h b/net/disk_cache/simple/simple_index.h
index b8f08a3..2f24897 100644
--- a/net/disk_cache/simple/simple_index.h
+++ b/net/disk_cache/simple/simple_index.h
@@ -181,6 +181,12 @@ class NET_EXPORT_PRIVATE SimpleIndex
   // background we can write the index much more frequently, to insure fresh
   // index on next startup.
   bool app_on_background_;
+
+  // The time in milliseconds for the index to be idle before it gets flushed to
+  // the disk. When the app is on foreground the delay is different from the
+  // background state.
+  int foreground_flush_delay_;
+  int background_flush_delay_;
 };
 
 }  // namespace disk_cache