AbstractSelectionKey.java

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package java.nio.channels.spi;

import java.nio.channels.SelectionKey;

/**
 * Base implementation class for selection keys.
 *
 * <p> This class tracks the validity of the key and implements cancellation.
 *
 * @author Mark Reinhold
 * @author JSR-51 Expert Group
 * @since 1.4
 */
// "选择键"SelectionKey的抽象实现
public abstract class AbstractSelectionKey extends SelectionKey {
    
    // 标记当前"选择键"的状态是否有效
    private volatile boolean valid = true;
    
    /**
     * Initializes a new instance of this class.
     */
    protected AbstractSelectionKey() {
    }
    
    // 判断当前"选择键"对象是否有效
    public final boolean isValid() {
        return valid;
    }
    
    // 将当前"选择键"对象标记为无效
    void invalidate() {
        valid = false;
    }
    
    /**
     * Cancels this key.
     *
     * If this key has not yet been cancelled then it is added to its selector's cancelled-key set while synchronized on that set.
     */
    // 取消当前"选择键"对象，取消之后其状态变为无效
    public final void cancel() {
        /*
         * Synchronizing "this" to prevent this key from getting canceled multiple times by different threads,
         * which might cause race condition between selector's select() and channel's close().
         */
        synchronized(this) {
            if(valid) {
                valid = false;
                ((AbstractSelector) selector()).cancel(this);
            }
        }
    }
    
}