See JDK-8039086 for some background.

The issue here is that the following code is not thread safe. A second thread can read cacheJavaTestTimeoutFactor as having the value 1 while it is still being set up by the first thread.

   protected float getTimeoutFactor() {
        if (cacheJavaTestTimeoutFactor == -1) {
            cacheJavaTestTimeoutFactor = 1; // default
            try {
                // use [1] to get the floating point timeout factor
                String f = (regEnv == null ? null : regEnv.lookup("javatestTimeoutFactor")[1]);
                if (f != null)
                    cacheJavaTestTimeoutFactor = Float.parseFloat(f);
            } catch (TestEnvironment.Fault e) {
            } catch (NumberFormatException e) {
            }
        }
        return cacheJavaTestTimeoutFactor;
    }

    private static float cacheJavaTestTimeoutFactor = -1;