jnr.ffi.annotations.Out Maven / Gradle / Ivy
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/*
* Copyright (C) 2008-2010 Wayne Meissner
*
* This file is part of the JNR project.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package jnr.ffi.annotations;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Indicates that the parameter is an OUT parameter.
*
* When a java object is passed to a native function as a pointer
* (for example {@link jnr.ffi.Pointer}, {@link jnr.ffi.Struct}, {@link java.nio.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 {@code @Out} so there is only copied {@code OUT}
* from native memory to java memory after the call, and the unneccessary copy {@code IN}
* from java to native memory before the call can be avoided.
*
*
Parameters with neither a {@code @In} nor a {@code @Out} annotation will copy both ways.
*
* @see In
* @see Clear
*/
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.PARAMETER, ElementType.METHOD, ElementType.ANNOTATION_TYPE })
public @interface Out {
}