Fix thread priorities for unstarted threads.

Calls to Thread.setPriority for unstarted threads now behave
similar to dalvik. Note that there's still some inconsistent
behaviour carried over from dalvik.

- high priority threads from bg_non_interactive processes are
  not always moved to the SP_FOREGROUND cgroup.
- we do not attempt to adjust the cgroup of a native thread
  that's attaching.

Note that on android, the system_server will change the
cgroups for all running threads in a process when it moves
into the foreground and background. It's by design that
threads in a background process can request to be moved
to the foreground by setting a higher priority.

bug: 17893086

(cherry picked from commit 1bd326a5e2aaff06a5bcae9cb2c42a4e8de31401)

Change-Id: Iad362f7c5c8697c349f2b6d7fcba69a4e141883e

2 files changed, 10 insertions, 0 deletions

diff --git a/runtime/thread.cc b/runtime/thread.cc
index 7d24562..2c44f27 100644
--- a/runtime/thread.cc
+++ b/runtime/thread.cc
@@ -170,6 +170,9 @@ void* Thread::CreateCallback(void* arg) {
     self->GetJniEnv()->DeleteGlobalRef(self->tlsPtr_.jpeer);
     self->tlsPtr_.jpeer = nullptr;
     self->SetThreadName(self->GetThreadName(soa)->ToModifiedUtf8().c_str());
+
+    mirror::ArtField* priorityField = soa.DecodeField(WellKnownClasses::java_lang_Thread_priority);
+    self->SetNativePriority(priorityField->GetInt(self->tlsPtr_.opeer));
     Dbg::PostThreadStart(self);
 
     // Invoke the 'run' method of our java.lang.Thread.
diff --git a/runtime/thread_android.cc b/runtime/thread_android.cc
index 73a9e54..d5db983 100644
--- a/runtime/thread_android.cc
+++ b/runtime/thread_android.cc
@@ -55,6 +55,13 @@ void Thread::SetNativePriority(int newPriority) {
   int newNice = kNiceValues[newPriority-1];
   pid_t tid = GetTid();
 
+  // TODO: b/18249098 The code below is broken. It uses getpriority() as a proxy for whether a
+  // thread is already in the SP_FOREGROUND cgroup. This is not necessarily true for background
+  // processes, where all threads are in the SP_BACKGROUND cgroup. This means that callers will
+  // have to call setPriority twice to do what they want :
+  //
+  //     Thread.setPriority(Thread.MIN_PRIORITY);  // no-op wrt to cgroups
+  //     Thread.setPriority(Thread.MAX_PRIORITY);  // will actually change cgroups.
   if (newNice >= ANDROID_PRIORITY_BACKGROUND) {
     set_sched_policy(tid, SP_BACKGROUND);
   } else if (getpriority(PRIO_PROCESS, tid) >= ANDROID_PRIORITY_BACKGROUND) {