Change the code as follows:
void stopTransport() { <- one of the template methods
stop(); <- abstract method is called
if (state.equals(State.STARTED)) {
state = State.STOPPED; <- state is changed without knowing the
status of stop() call
} else {
throw new IllegalStateException("Cannot stop transport " + id +
". Current state: " + state);
}
}
>From the stop() method above, if something fails, throw a RuntimeException.
On Tue, Dec 8, 2015 at 3:50 PM, Samiyuru Senarathne <[email protected]>
wrote:
> Hi,
>
> CarbonTransport [1] class in carbon-kernel implements template pattern and
> it has the following abstract methods.
>
> - protected abstract void start();
> - protected abstract void stop();
> - protected abstract void beginMaintenance();
> - protected abstract void endMaintenance();
>
> These abstract methods should be implemented by any class that implements
> a carbon transport. (For example NettyListener [2] does this). These
> abstract methods are called by the template methods of CarbonTransport
> class. These template methods maintain the state of the carbon transport as
> shown in the following code block.
>
> void stopTransport() { <- one of the template methods
> if (state.equals(State.STARTED)) {
> state = State.STOPPED; <- state is changed without knowing
> the status of stop() call
> } else {
> throw new IllegalStateException("Cannot stop transport " + id
> + ". Current state: " + state);
> }
> stop(); <- abstract method is called
> }
>
> As shown in the above code block CarbonTransport's template functions
> change the state of the transport without knowing the actual state of the
> transport after invoking the abstract function (assuming the abstract
> method call succeeded).
>
> IMO this behaviour can produce invalid states when the operations of the
> abstract method implementations do not complete as expected. IMO in order
> to fix this we can introduce an exception type to the abstract method's
> signature for the implementations to notify any failure or add a state
> return to the signature.
>
> - protected abstract void start() throws CarbonTransportException;
> - protected abstract void stop() throws CarbonTransportException;
> - protected abstract void beginMaintenance()
> throws CarbonTransportException;
> - protected abstract void endMaintenance()
> throws CarbonTransportException;
>
> Or
>
> - protected abstract State start();
> - protected abstract State stop();
> - protected abstract State beginMaintenance();
> - protected abstract State endMaintenance();
>
>
> WDYT?
>
> [1] -
> https://github.com/wso2/carbon-kernel/blob/master/core/src/main/java/org/wso2/carbon/kernel/transports/CarbonTransport.java
> [2] -
> https://github.com/wso2/carbon-transports/blob/master/http/netty/component/src/main/java/org/wso2/carbon/transport/http/netty/listener/NettyListener.java
>
> Thank you.
>
> Best Regards,
> Samiyuru
>
> --
> Samiyuru Senarathne
> *Software Engineer*
> Mobile : +94 (0) 71 134 6087
> [email protected]
>
--
*Afkham Azeez*
Director of Architecture; WSO2, Inc.; http://wso2.com
Member; Apache Software Foundation; http://www.apache.org/
* <http://www.apache.org/>*
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