private SpanEvent traceBlockBegin0(final int stackId) {
        if (closed) {
            if (logger.isWarnEnabled()) {
                stackDump("already closed trace");
            }
            return dummySpanEvent();
        }
        // Set properties for the case when stackFrame is not used as part of Span.
        final SpanEvent spanEvent = newSpanEvent(stackId);
        this.callStack.push(spanEvent);
        return spanEvent;
    }
@author netspider
@author emeroad
@author jaehong.kim
agent-module/profiler/src/main/java/com/navercorp/pinpoint/profiler/context/DefaultTrace.java