base: Support setting thread priorities generically.

base/threading/platform_thread_posix.cc

Index: base/threading/platform_thread_posix.cc
diff --git a/base/threading/platform_thread_posix.cc b/base/threading/platform_thread_posix.cc
index 0fb2a8a2258068af1a1393201b530483d0d475f7..5f4b6d1d18768b04e821533d78e40816073a599f 100644
--- a/base/threading/platform_thread_posix.cc
+++ b/base/threading/platform_thread_posix.cc
@@ -30,6 +30,7 @@
 
 #if defined(OS_ANDROID)
 #include <sys/resource.h>
+#include "base/android/jni_android.h"
 #include "base/android/thread_utils.h"
 #include "jni/ThreadUtils_jni.h"
 #endif
@@ -53,48 +54,73 @@ struct ThreadParams {
   ThreadPriority priority;
 };
 
-void SetCurrentThreadPriority(ThreadPriority priority) {
-#if defined(OS_LINUX) || defined(OS_ANDROID)
+
+int NiceValue(ThreadPriority priority) {
+  // These nice values are taken from Android, which uses nice
+  // values like linux, but defines some preset nice values.
+  //   Process.THREAD_PRIORITY_AUDIO = -16
+  //   Process.THREAD_PRIORITY_BACKGROUND = 10
+  //   Process.THREAD_PRIORITY_DEFAULT = 0;
+  //   Process.THREAD_PRIORITY_DISPLAY = -4;
+  //   Process.THREAD_PRIORITY_FOREGROUND = -2;
+  //   Process.THREAD_PRIORITY_LESS_FAVORABLE = 1;
+  //   Process.THREAD_PRIORITY_LOWEST = 19;
+  //   Process.THREAD_PRIORITY_MORE_FAVORABLE = -1;
+  //   Process.THREAD_PRIORITY_URGENT_AUDIO = -19;
+  //   Process.THREAD_PRIORITY_URGENT_DISPLAY = -8;
+  // We use -6 for display, but we may want to split this

[jar (doing other things), 2013/04/24 01:04:57]

This comment does not relate well to line 64 or 70.  You are not using -6 for
anything now.

[epenner, 2013/04/30 04:37:08]

Thanks! This was a typo. It should be -6 below.

Done.

+  // into urgent (-8) and non-urgent (-4).
+#if defined(OS_ANDROID)
+  static const int threadPriorityAudio = -16;
+#else
+  // TODO(epenner): Can we just use -16 on linux as well?
+  static const int threadPriorityAudio = -10;
+#endif
+  static const int threadPriorityBackground = 10;
+  static const int threadPriorityDefault = 0;
+  static const int threadPriorityDisplay = 6;
   switch (priority) {
-    case kThreadPriority_Normal:
-      NOTREACHED() << "Don't reset priority as not all processes can.";
-      break;
     case kThreadPriority_RealtimeAudio:
-#if defined(OS_LINUX)
-      const int kNiceSetting = -10;
-      // Linux isn't posix compliant with setpriority(2), it will set a thread
-      // priority if it is passed a tid, 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.
-      if (setpriority(PRIO_PROCESS, PlatformThread::CurrentId(), kNiceSetting))
-        DVLOG(1) << "Failed to set nice value of thread to " << kNiceSetting;
-#elif defined(OS_ANDROID)
-      JNIEnv* env = base::android::AttachCurrentThread();
-      Java_ThreadUtils_setThreadPriorityAudio(env, PlatformThread::CurrentId());
-#endif  // defined(OS_LINUX)
-      break;
+      return threadPriorityAudio;
+    case kThreadPriority_Background:
+      return threadPriorityBackground;
+    case kThreadPriority_Normal:
+      return threadPriorityDefault;
+    case kThreadPriority_Display:
+      return threadPriorityDisplay;
+    default:
+      NOTREACHED() << "Unknown priority.";
+      return 0;
   }
-#else  // !defined(OS_LINUX) && !defined(OS_ANDROID)
-  PlatformThread::SetThreadPriority(pthread_self(), priority);
-#endif
 }
 
 void* ThreadFunc(void* params) {
-#if defined(OS_ANDROID)
-  // Threads on linux/android may inherit their priority from the thread
-  // where they were created. This sets all threads to the default.
-  // TODO(epenner): Move thread priorities to base. (crbug.com/170549)
-  if (setpriority(PRIO_PROCESS, PlatformThread::CurrentId(), 0))
-    DVLOG(1) << "Failed to reset initial thread nice value to zero.";
-#endif
   ThreadParams* thread_params = static_cast<ThreadParams*>(params);
   PlatformThread::Delegate* delegate = thread_params->delegate;
   if (!thread_params->joinable)
     base::ThreadRestrictions::SetSingletonAllowed(false);
 
-  // If there is a non-default priority for this thread, set it now.
-  if (thread_params->priority != kThreadPriority_Normal)
-    SetCurrentThreadPriority(thread_params->priority);
+#if defined(OS_ANDROID) || defined(OS_LINUX)
+  // Threads on linux/android may inherit their priority from the thread
+  // where they were created. We may also not be allowed to set the
+  // priority on some processes, so we query it first and only
+  // change it if needed.
+  errno = 0; // getpriority may return -1 so we need to use errno.
+  int prio = getpriority(PRIO_PROCESS, PlatformThread::CurrentId());
+  bool error = prio == -1 && errno != 0;
+  if (error)
+    LOG(ERROR) << "Failed to get thread nice value";
+  // Set the priority if needed
+  if (!error && prio != NiceValue(thread_params->priority)) {

[jar (doing other things), 2013/04/24 01:04:57]

nit: Given the up-front-comment, I'd rather see an "else if" than see a repeat
test for "if (!error && ...". 

[epenner, 2013/04/30 04:37:08]

This has moved into SetThreadPriority now, I think I address ed this there (in
the _platform.cc files).

+    PlatformThread::SetThreadPriority(pthread_self(),
+                                      PlatformThread::CurrentId(),
+                                      thread_params->priority);
+  }
+#else
+  PlatformThread::SetThreadPriority(pthread_self(),
+                                    PlatformThread::CurrentId(),
+                                    thread_params->priority);
+#endif
 
   delete thread_params;
   delegate->ThreadMain();
@@ -292,11 +318,30 @@ void PlatformThread::Join(PlatformThreadHandle thread_handle) {
   pthread_join(thread_handle, NULL);
 }
 
-#if !defined(OS_MACOSX) && !defined(OS_ANDROID)
-// Mac OS X uses lower-level mach APIs and Android uses Java APIs.
-// static
-void PlatformThread::SetThreadPriority(PlatformThreadHandle, ThreadPriority) {
-  // TODO(crogers): Implement, see http://crbug.com/116172
+#if !defined(OS_MACOSX)
+// Mac OS X uses lower-level mach APIs
+void PlatformThread::SetThreadPriority(PlatformThreadHandle,
+                                       PlatformThreadId id,
+                                       ThreadPriority priority) {
+  // 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.
+#if defined(OS_ANDROID)
+  // On Android, we set the Audio priority through JNI as Audio priority
+  // will also allow the process to run while it is backgrounded.
+  if (priority == kThreadPriority_RealtimeAudio) {
+    JNIEnv* env = base::android::AttachCurrentThread();
+    Java_ThreadUtils_setThreadPriorityAudio(env, PlatformThread::CurrentId());
+    return;
+  }
+#endif
+#if !defined(OS_NACL)
+  DCHECK_NE(id, kInvalidThreadId);
+  int kNiceSetting = NiceValue(priority);
+  if (setpriority(PRIO_PROCESS, id, kNiceSetting))
+    LOG(ERROR) << "Failed to set nice value of thread to " << kNiceSetting;

[jar (doing other things), 2013/04/24 01:04:57]

DLOG is generally preferred.  No one will read this in production, so we'd
rather have this compiled out.

[epenner, 2013/04/30 04:37:08]

Done.

+#endif
 }
 #endif