docs: public static synchronized POSIX jnr() {
          if (posix == null) {
              posix = POSIXFactory.getPOSIX(new DefaultPOSIXHandler() {
                  @Override public void error(Errno error, String extraData) {
                      throw new PosixException("native error " + error.description() + " " + extraData, convert(error));
                  }
                  @Override public void error(Errno error, String methodName, String extraData) {
                      throw new PosixException("native error calling " + methodName + ": " + error.description() + " " + extraData, convert(error));
                  }
                  private org.jruby.ext.posix.POSIX.ERRORS convert(Errno error) {
                      try {
                          return org.jruby.ext.posix.POSIX.ERRORS.valueOf(error.name());
                      } catch (IllegalArgumentException x) {
                          return org.jruby.ext.posix.POSIX.ERRORS.EIO; // PosixException.message has real error anyway
                      }
                  }
              }, true);
          }
          return posix;
      }