Add a DCHECK for PlatformThread instances that are too busy.

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 52f88106b7cab16f34fc4c3e2b233ba047a1a642..5c95c5f156119a5257b9f75a778bf6ff29ed7eb2 100644
--- a/webrtc/base/platform_thread.cc
+++ b/webrtc/base/platform_thread.cc
@@ -10,8 +10,11 @@
 
 #include "webrtc/base/platform_thread.h"
 
+#include <inttypes.h>

[the sun, 2017/03/01 23:31:36]

stdint.h

[tommi, 2017/03/02 14:11:59]

removed now

+
 #include "webrtc/base/atomicops.h"
 #include "webrtc/base/checks.h"
+#include "webrtc/base/timeutils.h"
 
 #if defined(WEBRTC_LINUX)
 #include <sys/prctl.h>
@@ -220,26 +223,42 @@ void PlatformThread::Run() {
     run_function_(obj_);
     return;
   }
-// TODO(tommi): Delete the below.
-#if !defined(WEBRTC_MAC) && !defined(WEBRTC_WIN)
-  const struct timespec ts_null = {0};
+
+  // TODO(tommi): Delete the rest of this function when looping isn't supported.
+#if RTC_DCHECK_IS_ON
+  static const int kMaxLoopCount = 1000;
+  static const int kPeriodToMeasureMs = 100;
+  int64_t loop_stamps[kMaxLoopCount] = {};
+  int64_t sequence_nr = 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
     // call the function before checking |stop_|.
     if (!run_function_deprecated_(obj_))
       break;
+#if RTC_DCHECK_IS_ON

[the sun, 2017/03/01 23:31:36]

A comment wouldn't hurt, considering the above constants are empirical. E.g.
// We consider threads iterating more often than 100ms to be "busy", but only
after 1000 iterations.

[tommi, 2017/03/02 14:11:59]

Done.

+    auto id = sequence_nr % kMaxLoopCount;
+    loop_stamps[id] = rtc::TimeMillis();
+    if (sequence_nr > kMaxLoopCount) {
+      auto compare_id = (id + 1) % kMaxLoopCount;
+      auto diff = loop_stamps[id] - loop_stamps[compare_id];

[the sun, 2017/03/01 23:31:36]

Why do you store the whole sequence, when you're only comparing against the last
time stamp?

[tommi, 2017/03/02 14:11:59]

Since this is a sliding window, the last time stamp is kMaxLoopCount-1 stamps
away, so we need to know all the stamps.  We compare against all of them, but
only one of them at a time.

[the sun, 2017/03/02 14:20:09]

Ah, got the indices wrong - thanks for explaining.

+      RTC_DCHECK_GE(diff, 0);
+      if (diff < kPeriodToMeasureMs) {
+        RTC_NOTREACHED() << "This thread is too busy: " << name_ << " " << diff
+          << "ms sequence=" << sequence_nr << " " << loop_stamps[id] << " vs "
+          << loop_stamps[compare_id] << ", " << 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(WEBRTC_MAC)
     sched_yield();
-#else
-    nanosleep(&ts_null, nullptr);
-#endif
   } while (!AtomicOps::AcquireLoad(&stop_flag_));
 #endif  // defined(WEBRTC_WIN)
 }