Fix NiceValueToThreadPriority failing on an unknown nice value.

base/threading/platform_thread_internal_posix.cc

 // Copyright 2015 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/threading/platform_thread_internal_posix.h"
 
+#include <limits>
 #include "base/logging.h"

[gab, 2016/04/12 13:20:46]

nit: empty line between C++ includes and Chrome includes

[Yuta Kitamura, 2016/04/13 08:49:17]

Done.

 
 namespace base {
 
 namespace internal {
 
 int ThreadPriorityToNiceValue(ThreadPriority priority) {
   for (const ThreadPriorityToNiceValuePair& pair :
        kThreadPriorityToNiceValueMap) {
     if (pair.priority == priority)
       return pair.nice_value;
   }
   NOTREACHED() << "Unknown ThreadPriority";
   return 0;
 }
 
 ThreadPriority NiceValueToThreadPriority(int nice_value) {
+  // Try to find a priority that best describes |nice_value|. If there isn't
+  // an exact match, this method returns the closest priority whose nice value
+  // is higher (lower priority) than |nice_value|.
+
+  ThreadPriority best_priority = ThreadPriority::BACKGROUND;
+  int best_nice_value = std::numeric_limits<int>::max();
   for (const ThreadPriorityToNiceValuePair& pair :

[danakj, 2016/04/12 21:02:26]

this should use const auto&

[Yuta Kitamura, 2016/04/13 08:49:17]

Done.

        kThreadPriorityToNiceValueMap) {

[danakj, 2016/04/12 21:02:26]

if you base::Reversed this to iterate opposite, you don't need to store a
best_priority, right? You just return the first one that is >= nice_value. If
you exit the loop without finding one you return background?

[Yuta Kitamura, 2016/04/13 08:49:17]

Yeah, that's much simpler. Thanks!

-    if (pair.nice_value == nice_value)
-      return pair.priority;
+    if (pair.nice_value >= nice_value) {
+      DCHECK_LT(pair.nice_value, best_nice_value);
+      best_priority = pair.priority;
+      best_nice_value = pair.nice_value;
+    } else {
+      break;
+    }
   }
-  NOTREACHED() << "Unknown nice value";
-  return ThreadPriority::NORMAL;
+  return best_priority;
 }
 
 }  // namespace internal
 
 }  // namespace base