jnr.ffi.annotations

Annotation Type Out

@Retention(value=RUNTIME)
@Target(value={PARAMETER,METHOD,ANNOTATION_TYPE})
public @interface Out

Indicates that the parameter is an OUT parameter.

When a java object is passed to a native function as a pointer (for example Pointer, Struct, ByteBuffer), then a temporary native memory block is allocated, the java data is copied to the temporary memory and the address of the temporary memory is passed to the function. After the function returns, the java data is automatically updated from the contents of the native memory.

As this extra copying can be expensive, for native functions which only write to the passed in memory block and do not use the existing contents, parameters can be annotated with @Out so there is only copied OUT from native memory to java memory after the call, and the unneccessary copy IN from java to native memory before the call can be avoided.

Parameters with neither a @In nor a @Out annotation will copy both ways.

See Also:

In, Clear