IOStatus.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package sun.nio.ch;

import java.lang.annotation.Native;

/** Constants for reporting I/O status */
// 底层IO操作返回的状态
public final class IOStatus {
    
    @Native
    public static final int EOF = -1;      // End of file
    @Native
    public static final int UNAVAILABLE = -2;      // Nothing available (non-blocking)
    @Native
    public static final int INTERRUPTED = -3;      // System call interrupted(这是系统中断标记，不是普通的线程中断标记)
    @Native
    public static final int UNSUPPORTED = -4;      // Operation not supported
    @Native
    public static final int THROWN = -5;      // Exception thrown in JNI code
    @Native
    public static final int UNSUPPORTED_CASE = -6; // This case not supported
    
    
    private IOStatus() {
    }
    
    /*
     * The following two methods are for use in try/finally blocks where a
     * status value needs to be normalized before being returned to the invoker
     * but also checked for illegal negative values before the return
     * completes, like so:
     *
     *     int n = 0;
     *     try {
     *         begin();
     *         n = op(fd, buf, ...);
     *         return IOStatus.normalize(n);    // Converts UNAVAILABLE to zero
     *     } finally {
     *         end(n > 0);
     *         assert IOStatus.check(n);        // Checks other negative values
     *     }
     *
     */
    
    // 将底层返回的状态标记规范化
    public static int normalize(int n) {
        if(n == UNAVAILABLE) {
            return 0;
        }
        return n;
    }
    
    // 将底层返回的状态标记规范化
    public static long normalize(long n) {
        if(n == UNAVAILABLE) {
            return 0;
        }
        return n;
    }
    
    // 检查是否可以正常I/O（不存在异常、中断、不支持的情形）
    public static boolean check(int n) {
        return (n >= UNAVAILABLE);
    }
    
    // 检查是否可以正常I/O（不存在异常、中断、不支持的情形）
    public static boolean check(long n) {
        return (n >= UNAVAILABLE);
    }
    
    // Return true if n is not one of the IOStatus values
    public static boolean checkAll(long n) {
        return ((n>EOF) || (n<UNSUPPORTED_CASE));
    }
    
}