// local variable: the field lastSourceValue is not
// reliable as it might be mutated by multipled threads.
// The lastSourceValue field is only accessed by tests,
// so this is not a concern.
IntegralDataTypeHolder value = null;
while ( value == null || value.lt( 1 ) ) {
value = callback.getNextValue();
}
lastSourceValue = value;
return value.makeValue();
}