Linux, Android: fix call to setpriority(2).

base/threading/platform_thread_android.cc

Index: base/threading/platform_thread_android.cc
diff --git a/base/threading/platform_thread_android.cc b/base/threading/platform_thread_android.cc
index bd0b4b33db74a137fa1dd0508f39586362857d5a..87a1c5d16195b50f88867385ce8d3dcde7ace669 100644
--- a/base/threading/platform_thread_android.cc
+++ b/base/threading/platform_thread_android.cc
@@ -65,13 +65,13 @@ void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
     return;
   }
 
-  // setpriority(2) will set a thread's priority if it is passed a tid as
-  // the 'process identifier', not affecting the rest of the threads in the
-  // process. Setting this priority will only succeed if the user has been
-  // granted permission to adjust nice values on the system.
+  // setpriority(2) should change the whole thread group's (i.e. process)
+  // priority. However, on Linux it will only change the current thread. See
+  // the BUGs section in
+  // http://man7.org/linux/man-pages/man2/getpriority.2.html.
   DCHECK_NE(handle.id_, kInvalidThreadId);
   int kNiceSetting = ThreadNiceValue(priority);
-  if (setpriority(PRIO_PROCESS, handle.id_, kNiceSetting))
+  if (setpriority(PRIO_PROCESS, 0, kNiceSetting))

[mdempsky, 2014/08/01 00:05:32]

Can SetThreadPriority() be called by a different thread?  Should there be an
assert to check that handle.id_ == gettid(), or maybe even just use

    handle.id_ == gettid() ? 0 : handle.id_

with a comment that we prefer to use 0 if possible because it allows tighter
sandbox policies?

(Same comment on the _linux.cc file.)

[jln (very slow on Chromium), 2014/08/01 00:39:53]

Ooch. I was a little hasty on this one indeed, thanks.

     LOG(ERROR) << "Failed to set nice value of thread to " << kNiceSetting;
 }