OpenJDK8 crashes with -XX:+EnableTracing

Reported by Xin Liu (xxinliu@amazon.com).

If you invoke java with the option -XX:+EnableTracing, it will crash immediately. It's because events XXXFlagChanged doesn't work in the initial thread.

class EventBooleanFlagChanged : public TraceEvent<EventBooleanFlagChanged>
  EventBooleanFlagChanged(EventStartTime timing=TIMED) : TraceEvent<EventBooleanFlagChanged>(timing) {}

  void writeEvent(void) {
    ResourceMark rm;
    if (UseLockedTracing) {
      ttyLocker lock;
      writeEventContent();
    } else {
      writeEventContent();
    }
  }
};

The ResourceMark won't work if Thread::current() is NULL.

A simple patch for OpenJDK follows, but won't work for OracleJDK.

diff --git a/src/hotspot/src/share/vm/runtime/globals.cpp b/src/hotspot/src/share/vm/runtime/globals.cpp
index 310fc2ea..6f89c275 100644
--- a/src/hotspot/src/share/vm/runtime/globals.cpp
+++ b/src/hotspot/src/share/vm/runtime/globals.cpp
@@ -608,12 +608,12 @@ bool CommandLineFlags::wasSetOnCmdline(const char* name, bool* value) {
 template<class E, class T>
 static void trace_flag_changed(const char* name, const T old_value, const T new_value, const Flag::Flags origin)
 {
- E e;
- e.set_name(name);
- e.set_old_value(old_value);
- e.set_new_value(new_value);
- e.set_origin(origin);
- e.commit();
+ //E e;
+ //e.set_name(name);
+ //e.set_old_value(old_value);
+ //e.set_new_value(new_value);
+ //e.set_origin(origin);
+ //e.commit();
 }
 
 bool CommandLineFlags::boolAt(const char* name, size_t len, bool* value) {