Replace the stop_event_ in PlatformThread with an atomic flag

webrtc/base/platform_thread.cc

Index: webrtc/base/platform_thread.cc
diff --git a/webrtc/base/platform_thread.cc b/webrtc/base/platform_thread.cc
index 0b025f2af048f94d9e776f171276850f54ef952e..d1bd509bf1ad301591b0c4be6e648218cb196de4 100644
--- a/webrtc/base/platform_thread.cc
+++ b/webrtc/base/platform_thread.cc
@@ -10,6 +10,7 @@
 
 #include "webrtc/base/platform_thread.h"
 
+#include "webrtc/base/atomicops.h"
 #include "webrtc/base/checks.h"
 
 #if defined(WEBRTC_LINUX)
@@ -96,15 +97,7 @@ PlatformThread::PlatformThread(ThreadRunFunction func,
                                const char* thread_name)
     : run_function_(func),
       obj_(obj),
-      name_(thread_name ? thread_name : "webrtc"),
-#if defined(WEBRTC_WIN)
-      stop_(false),
-      thread_(NULL),
-      thread_id_(0) {
-#else
-      stop_event_(false, false),
-      thread_(0) {
-#endif  // defined(WEBRTC_WIN)
+      name_(thread_name ? thread_name : "webrtc") {
   RTC_DCHECK(func);
   RTC_DCHECK(name_.length() < 64);
 }
@@ -187,15 +180,26 @@ void PlatformThread::Stop() {
   thread_ = nullptr;
   thread_id_ = 0;
 #else
-  stop_event_.Set();
+  RTC_CHECK_EQ(1, AtomicOps::Increment(&stop_flag_));
   RTC_CHECK_EQ(0, pthread_join(thread_, nullptr));
+  AtomicOps::ReleaseStore(&stop_flag_, 0);
   thread_ = 0;
 #endif  // defined(WEBRTC_WIN)
 }
 
+// TODO(tommi): Deprecate the loop behavior in PlatformThread.
+// * Introduce a new callback type that returns void.
+// * Remove potential for a busy loop in PlatformThread.
+// * Delegate the responsibility for how to stop the thread, to the
+//   implementation that actually uses the thread.
+// All implementations will need to be aware of how the thread should be stopped
+// and encouraging a busy polling loop, can be costly in terms of power and cpu.
 void PlatformThread::Run() {
   if (!name_.empty())
     rtc::SetCurrentThreadName(name_.c_str());
+#if !defined(WEBRTC_MAC) && !defined(WEBRTC_WIN)
+  const struct timespec ts_null = {0};
+#endif
   do {
     // The interface contract of Start/Stop is that for a successful call to
     // Start, there should be at least one call to the run function.  So we
@@ -207,7 +211,12 @@ void PlatformThread::Run() {
     SleepEx(0, true);
   } while (!stop_);
 #else
-  } while (!stop_event_.Wait(0));
+#if defined(WEBRTC_MAC)
+    sched_yield();
+#else
+    nanosleep(&ts_null, nullptr);
+#endif
+  } while (!AtomicOps::AcquireLoad(&stop_flag_));
 #endif  // defined(WEBRTC_WIN)
 }