posix thread: Attempt to set audio threads to real time.

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"
@@ skipping 58 matching lines @@
   // We expect EPERM failures in sandboxed processes, just ignore those.
   if (err < 0 && errno != EPERM)
     DPLOG(ERROR) << "prctl(PR_SET_NAME)";
 #endif
 }
 
 // static
 void PlatformThread::SetThreadPriority(PlatformThreadHandle handle,
                                        ThreadPriority priority) {
 #ifndef OS_NACL
+  if (priority == kThreadPriority_RealtimeAudio) {
+    const int kRealTimePrio = 8;
+
+    struct sched_param sched_param;
+    memset(&sched_param, 0, sizeof(sched_param));
+    sched_param.sched_priority = kRealTimePrio;
+
+    int res = pthread_setschedparam(pthread_self(), SCHED_RR, &sched_param);
+    if (res == 0)
+      // Got real time priority, no need to set nice level.
+      return;

[piman, 2013/05/28 21:58:56]

nit: need braces if the clause takes multiple lines.

[dgreid, 2013/05/28 22:18:53]

Done.

+    else
+      LOG(INFO) << "Failed to set audio thread to real time.";
+
+#if defined(OS_CHROMEOS)
+    DCHECK_EQ(res, 0);  // RT prio should always work on ChromeOS.

[piman, 2013/05/28 21:58:56]

This prevents debugging chromeos=1 builds on the desktop.
We're already logging if it fails, that's enough IMO.

[dgreid, 2013/05/28 22:18:53]

Good point, switched this back to a return.

+#endif
+  }
+
   // 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.
   DCHECK_NE(handle.id_, kInvalidThreadId);
   int kNiceSetting = ThreadNiceValue(priority);
   if (setpriority(PRIO_PROCESS, handle.id_, kNiceSetting))
     LOG(ERROR) << "Failed to set nice value of thread to " << kNiceSetting;
 #endif
 }
 
 void InitThreading() {
 }
 
 void InitOnThread() {
 }
 
 void TerminateOnThread() {
 }
 
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
   return 0;
 }
 
 }  // namespace base