Ensure profiler manager thread has shutdown before main thread

runtime/vm/profiler_linux.cc

Index: runtime/vm/profiler_linux.cc
diff --git a/runtime/vm/profiler_linux.cc b/runtime/vm/profiler_linux.cc
index 711dcc785982765c08d6220d391f975194e198e5..1eb650553f7c5502ac13d9fa0c39c2b39e216ac3 100644
--- a/runtime/vm/profiler_linux.cc
+++ b/runtime/vm/profiler_linux.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 Linux 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 Linux exiting.\n");
+  }
+  thread_running_ = false;
+  {
+    // Signal to main thread we are exiting.
+    ScopedMonitor shutdown_lock(start_stop_monitor_);
+    shutdown_lock.Notify();
+  }
 }