public int getConcurrency(int defaultValue) {
		return getProperty(CONCURRENCY, defaultValue);
	}
Return the 'concurrency' property or the default value.
The meaning of concurrency depends on the bus implementation.
@param defaultValue The default value.
@return The property or default value.
spring-xd-messagebus-spi/src/main/java/org/springframework/xd/dirt/integration/bus/AbstractBusPropertiesAccessor.java