Go back to only using sched_yield on Mac (sigh)

webrtc/base/platform_thread.cc

 /*
  *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 243 matching lines @@
                          << ", " << id << " vs " << compare_id;
       }
     }
     ++sequence_nr;
 #endif
 #if defined(WEBRTC_WIN)
     // Alertable sleep to permit RaiseFlag to run and update |stop_|.
     SleepEx(0, true);
   } while (!stop_);
 #else
-#if defined(UNDEFINED_SANITIZER) || defined(WEBRTC_ANDROID)
-    // UBSAN and Android don't like |sched_yield()| that much.
+#if defined(WEBRTC_MAC)
+    sched_yield();
+#else
     static const struct timespec ts_null = {0};
     nanosleep(&ts_null, nullptr);
-#else  // !(defined(UNDEFINED_SANITIZER) || defined(WEBRTC_ANDROID))
-    // Mac and Linux show better performance with sched_yield.
-    sched_yield();
 #endif
   } while (!AtomicOps::AcquireLoad(&stop_flag_));
 #endif  // defined(WEBRTC_WIN)
 }
 
 bool PlatformThread::SetPriority(ThreadPriority priority) {
 #if RTC_DCHECK_IS_ON
   if (run_function_) {
     // The non-deprecated way of how this function gets called, is that it must
     // be called on the worker thread itself.
@@ skipping 60 matching lines @@
 #if defined(WEBRTC_WIN)
 bool PlatformThread::QueueAPC(PAPCFUNC function, ULONG_PTR data) {
   RTC_DCHECK(thread_checker_.CalledOnValidThread());
   RTC_DCHECK(IsRunning());
 
   return QueueUserAPC(function, thread_, data) != FALSE;
 }
 #endif
 
 }  // namespace rtc