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- (oneway void)release;

"Synchronous and Asynchronous Messages

Consider first a method with just a simple return value:

- (BOOL)canDance;

When a canDance message is sent to a receiver in the same application, the method is invoked and the

return value provided directly to the sender. But when the receiver is in a remote application, two underlying

messages are required—one message to get the remote object to invoke the method, and the other message

to send back the result of the remote calculation. This is illustrated in the figure below:

<Figure 12-2>

Most remote messages are, at bottom, two-way (or “round trip”) remote procedure calls (RPCs) like this one.

The sending application waits for the receiving application to invoke the method, complete its processing,

and send back an indication that it has finished, along with any return information requested. Waiting for

the receiver to finish, even if no information is returned, has the advantage of coordinating the two

communicating applications, of keeping them both “in sync.” For this reason, round-trip messages are often

called synchronous. Synchronous messages are the default.

However, it’s not always necessary or a good idea to wait for a reply. Sometimes it’s sufficient simply to

dispatch the remote message and return, allowing the receiver to get to the task when it can. In the meantime,

the sender can go on to other things. Objective-C provides a return type modifier, oneway, to indicate that

a method is used only for asynchronous messages:

- (oneway void)waltzAtWill;

Although oneway is a type qualifier (like const) and can be used in combination with a specific type name,

such as oneway float or oneway id, the only such combination that makes any sense is oneway void.

An asynchronous message can’t have a valid return value."