base/threading: restrict to set only current thread priority

base/threading/platform_thread_linux.cc

 // Copyright (c) 2012 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.h"
 
 #include <errno.h>
 #include <sched.h>
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/threading/platform_thread_internal_posix.h"
 #include "base/threading/thread_id_name_manager.h"
 #include "base/tracked_objects.h"
 
 #if !defined(OS_NACL)
 #include <pthread.h>
 #include <sys/prctl.h>
 #include <sys/types.h>
 #include <unistd.h>
 #endif
 
 namespace base {
 
 namespace internal {
 
 namespace {
 #if !defined(OS_NACL)
 const struct sched_param kRealTimePrio = {8};
+const struct sched_param kResetPrio = {0};
 #endif
 }  // namespace
 
 const ThreadPriorityToNiceValuePair kThreadPriorityToNiceValueMap[4] = {
     {ThreadPriority::BACKGROUND, 10},
     {ThreadPriority::NORMAL, 0},
     {ThreadPriority::DISPLAY, -6},
     {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
   return false;
 #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 &&
       maybe_realtime_prio.sched_priority == kRealTimePrio.sched_priority) {
     *priority = ThreadPriority::REALTIME_AUDIO;
     return true;
   }
 #endif
   return false;
 }
@@ skipping 35 matching lines @@
 #if !defined(THREAD_SANITIZER)
   return 0;
 #else
   // ThreadSanitizer bloats the stack heavily. Evidence has been that the
   // default stack size isn't enough for some browser tests.
   return 2 * (1 << 23);  // 2 times 8192K (the default stack size on Linux).
 #endif
 }
 
 }  // namespace base