netty-incubator-buffer-api/src/main/java/io/netty/buffer/api/Rc.java

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/*
* Copyright 2020 The Netty Project
*
* The Netty Project licenses this file to you 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:
*
* https://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.
*/
2020-11-17 15:38:11 +01:00
package io.netty.buffer.api;
/**
* An Rc is a reference counted, thread-confined, resource of sorts. Because these resources are thread-confined, the
* reference counting is NOT atomic. An Rc can only be accessed by one thread at a time - the owner thread that the
* resource is confined to.
* <p>
* When the last reference is closed (accounted for using {@link AutoCloseable} and try-with-resources statements,
* ideally), then the resource is desposed of, or released, or returned to the pool it came from. The precise action is
* implemented by the {@link Drop} instance given as an argument to the Rc constructor.
*
* @param <I> The concrete subtype.
*/
public interface Rc<I extends Rc<I>> extends AutoCloseable, Deref<I> {
/**
* Increment the reference count.
* <p>
* Note, this method is not thread-safe because reference counted objects are meant to thread-confined.
*
* @return This Rc instance.
*/
I acquire();
@Override
default I get() {
return acquire();
}
@Override
default boolean isInstanceOf(Class<?> cls) {
return cls.isInstance(this);
}
/**
* Decrement the reference count, and despose of the resource if the last reference is closed.
* <p>
* Note, this method is not thread-safe because reference counted objects are meant to be thread-confined.
*
* @throws IllegalStateException If this Rc has already been closed.
*/
@Override
void close();
/**
* Send this reference counted object instance to another Thread, transferring the ownership to the recipient.
* <p>
* Note that the object must be {@linkplain #isOwned() owned}, and cannot have any outstanding borrows,
* when it's being sent.
* That is, all previous acquires must have been closed, and {@link #isOwned()} must return {@code true}.
* <p>
* This instance immediately becomes inaccessible, and all attempts at accessing this reference counted object
* will throw. Calling {@link #close()} will have no effect, so this method is safe to call within a
* try-with-resources statement.
*/
Send<I> send();
/**
* Check that this reference counted object is owned.
* <p>
* To be owned, the object must have no outstanding acquires, and no other implementation defined restrictions.
*
* @return {@code true} if this object can be {@linkplain #send() sent},
* or {@code false} if calling {@link #send()} would throw an exception.
*/
boolean isOwned();
/**
* Count the number of borrows of this object.
* Note that even if the number of borrows is {@code 0}, this object might not be {@linkplain #isOwned() owned}
* because there could be other restrictions involved in ownership.
*
* @return The number of borrows, if any, of this object.
*/
int countBorrows();
/**
* Check if this object is accessible.
*
* @return {@code true} if this object is still valid and can be accessed,
* otherwise {@code false} if, for instance, this object has been dropped/deallocated,
* or been {@linkplain #send() sent} elsewhere.
*/
boolean isAccessible();
}