base/threading: restrict to set only current thread priority

base/threading/platform_thread_linux.cc

Index: base/threading/platform_thread_linux.cc
diff --git a/base/threading/platform_thread_linux.cc b/base/threading/platform_thread_linux.cc
index 9f7437418a7299ec6ab92d80b1be6735f6b9b9fa..48cf7443f7d5156b31624318bc0a18d2aba35e5c 100644
--- a/base/threading/platform_thread_linux.cc
+++ b/base/threading/platform_thread_linux.cc
@@ -27,6 +27,7 @@ namespace internal {
 namespace {
 #if !defined(OS_NACL)
 const struct sched_param kRealTimePrio = {8};
+const struct sched_param kResetPrio = {0};
 #endif
 }  // namespace
 
@@ -37,11 +38,18 @@ const ThreadPriorityToNiceValuePair kThreadPriorityToNiceValueMap[4] = {
     {ThreadPriority::REALTIME_AUDIO, -10},
 };
 
-bool SetThreadPriorityForPlatform(PlatformThreadHandle handle,
-                                  ThreadPriority priority) {
+bool SetCurrentThreadPriorityForPlatform(ThreadPriority priority) {
 #if !defined(OS_NACL)
-  // TODO(gab): Assess the correctness of using |pthread_self()| below instead
-  // of |handle|. http://crbug.com/468793.
+  ThreadPriority current_priority;
+  if (priority != ThreadPriority::REALTIME_AUDIO &&
+      GetCurrentThreadPriorityForPlatform(&current_priority) &&
+      current_priority == ThreadPriority::REALTIME_AUDIO) {
+    // If the pthread's round-robin scheduler is already enabled, and the new
+    // priority will use setpriority() instead, the pthread scheduler should be
+    // reset to use SCHED_OTHER so that setpriority() just works.
+    pthread_setschedparam(pthread_self(), SCHED_OTHER, &kResetPrio);

[gab, 2015/06/23 17:01:32]

I think we should do a separate CL for actual logic changes which shouldn't be
mixed amongst mechanical API changes.

[Takashi Toyoshima, 2015/06/24 04:15:39]

Done.

+    return false;
+  }
   return priority == ThreadPriority::REALTIME_AUDIO  &&
          pthread_setschedparam(pthread_self(), SCHED_RR, &kRealTimePrio) == 0;
 #else
@@ -49,13 +57,10 @@ bool SetThreadPriorityForPlatform(PlatformThreadHandle handle,
 #endif
 }
 
-bool GetThreadPriorityForPlatform(PlatformThreadHandle handle,
-                                  ThreadPriority* priority) {
+bool GetCurrentThreadPriorityForPlatform(ThreadPriority* priority) {
 #if !defined(OS_NACL)
   int maybe_sched_rr = 0;
   struct sched_param maybe_realtime_prio = {0};
-  // TODO(gab): Assess the correctness of using |pthread_self()| below instead
-  // of |handle|. http://crbug.com/468793.
   if (pthread_getschedparam(pthread_self(), &maybe_sched_rr,
                             &maybe_realtime_prio) == 0 &&
       maybe_sched_rr == SCHED_RR &&