Ensure profiler manager thread has shutdown before main thread

runtime/vm/profiler_macos.cc

Index: runtime/vm/profiler_macos.cc
diff --git a/runtime/vm/profiler_macos.cc b/runtime/vm/profiler_macos.cc
index eb2888d1417f07cc35d427c44b1e69feee77e018..f891d6e46335ae5843baa797b0a5b790370e94f9 100644
--- a/runtime/vm/profiler_macos.cc
+++ b/runtime/vm/profiler_macos.cc
@@ -13,6 +13,7 @@
 namespace dart {
 
 DECLARE_FLAG(bool, profile);
+DECLARE_FLAG(bool, trace_profiled_isolates);
 
 static void CollectSample(IsolateProfilerData* profiler_data,
                           uintptr_t pc,
@@ -129,12 +130,30 @@ void ProfilerManager::ThreadMain(uword parameters) {
   ASSERT(initialized_);
   ASSERT(FLAG_profile);
   SignalHandler::Install(ProfileSignalAction);
+  if (FLAG_trace_profiled_isolates) {
+    OS::Print("ProfilerManager MacOS ready.\n");
+  }
+  thread_running_ = true;
+  {
+    // Signal to main thread we are ready.
+    ScopedMonitor startup_lock(start_stop_monitor_);
+    startup_lock.Notify();
+  }
   ScopedMonitor lock(monitor_);
   while (!shutdown_) {
     int64_t current_time = OS::GetCurrentTimeMicros();
     int64_t next_sample = SampleAndRescheduleIsolates(current_time);
     lock.WaitMicros(next_sample);
   }
+  if (FLAG_trace_profiled_isolates) {
+    OS::Print("ProfilerManager MacOS exiting.\n");
+  }
+  thread_running_ = false;
+  {
+    // Signal to main thread we are exiting.
+    ScopedMonitor shutdown_lock(start_stop_monitor_);
+    shutdown_lock.Notify();
+  }
 }