protected void writeThrowable(Throwable t, PrintStream targetStream) {
        if (t != null) {
            t.printStackTrace(targetStream);
        }
    }
To avoid intermingling of log messages and associated stack traces, the two
operations are done in a synchronized block.

@param buf
@param t
slf4j-simple/src/main/java/org/slf4j/simple/SimpleLogger.java