PipedWriter.java

/*
 * Copyright (c) 1996, 2016, Oracle and/or its affiliates. All rights reserved.
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.io;

/**
 * Piped character-output streams.
 *
 * @author Mark Reinhold
 * @since 1.1
 */
// (字符)写管道，需要与读管道配合使用
public class PipedWriter extends Writer {
    
    /*
     * REMIND: identification of the read and write sides needs to be more sophisticated.
     * Either using thread groups (but what about pipes within a thread?)
     * or using finalization (but it may be a long time until the next GC).
     */
    private PipedReader sink;   // 连接的读管道
    
    /*
     * This flag records the open status of this particular writer.
     * It is independent of the status flags defined in PipedReader.
     * It is used to do a sanity check on connect.
     */
    private boolean closed = false;
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Creates a piped writer that is not yet connected to a
     * piped reader. It must be connected to a piped reader,
     * either by the receiver or the sender, before being used.
     *
     * @see java.io.PipedReader#connect(java.io.PipedWriter)
     * @see java.io.PipedWriter#connect(java.io.PipedReader)
     */
    // 构造写管道，未与读管道建立连接
    public PipedWriter() {
    }
    
    /**
     * Creates a piped writer connected to the specified piped
     * reader. Data characters written to this stream will then be
     * available as input from <code>snk</code>.
     *
     * @param snk The piped reader to connect to.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 构造写管道，且与读管道建立连接
    public PipedWriter(PipedReader snk) throws IOException {
        connect(snk);
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 写 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Writes the specified <code>char</code> to the piped output stream.
     * If a thread was reading data characters from the connected piped input
     * stream, but the thread is no longer alive, then an
     * <code>IOException</code> is thrown.
     * <p>
     * Implements the <code>write</code> method of <code>Writer</code>.
     *
     * @param c the <code>char</code> to be written.
     *
     * @throws IOException if the pipe is
     *                     <a href=PipedOutputStream.html#BROKEN> <code>broken</code></a>,
     *                     {@link #connect(java.io.PipedReader) unconnected}, closed
     *                     or an I/O error occurs.
     */
    // 向读管道存入一个字符
    public void write(int c) throws IOException {
        if(sink == null) {
            throw new IOException("Pipe not connected");
        }
        
        // 将写入的字符保存到读管道的缓冲区
        sink.receive(c);
    }
    
    /**
     * Writes {@code len} characters from the specified character array
     * starting at offset {@code off} to this piped output stream.
     * This method blocks until all the characters are written to the output
     * stream.
     * If a thread was reading data characters from the connected piped input
     * stream, but the thread is no longer alive, then an
     * {@code IOException} is thrown.
     *
     * @param cbuf the data.
     * @param off  the start offset in the data.
     * @param len  the number of characters to write.
     *
     * @throws IndexOutOfBoundsException If {@code off} is negative, or {@code len} is negative,
     *                                   or {@code off + len} is negative or greater than the length
     *                                   of the given array
     * @throws IOException               if the pipe is
     *                                   <a href=PipedOutputStream.html#BROKEN><code>broken</code></a>,
     *                                   {@link #connect(java.io.PipedReader) unconnected}, closed
     *                                   or an I/O error occurs.
     */
    // 向读管道存入字符数组cbuf中off处起的len个字符
    public void write(char[] cbuf, int off, int len) throws IOException {
        if(sink == null) {
            throw new IOException("Pipe not connected");
        } else if((off | len | (off + len) | (cbuf.length - (off + len)))<0) {
            throw new IndexOutOfBoundsException();
        }
        
        // 将写入的字符保存到读管道的缓冲区
        sink.receive(cbuf, off, len);
    }
    
    /*▲ 写 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 杂项 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Closes this piped output stream and releases any system resources
     * associated with this stream. This stream may no longer be used for
     * writing characters.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 关闭写管道，并唤醒所有阻塞的线程
    public void close() throws IOException {
        closed = true;
        if(sink != null) {
            sink.receivedLast();
        }
    }
    
    /**
     * Flushes this output stream and forces any buffered output characters
     * to be written out.
     * This will notify any readers that characters are waiting in the pipe.
     *
     * @throws IOException if the pipe is closed, or an I/O error occurs.
     */
    // 刷新缓冲区，即唤醒读线程
    public synchronized void flush() throws IOException {
        if(sink != null) {
            if(sink.closedByReader || closed) {
                throw new IOException("Pipe closed");
            }
            
            synchronized(sink) {
                sink.notifyAll();
            }
        }
    }
    
    /*▲ 杂项 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 交互 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Connects this piped writer to a receiver. If this object
     * is already connected to some other piped reader, an
     * <code>IOException</code> is thrown.
     * <p>
     * If <code>snk</code> is an unconnected piped reader and
     * <code>src</code> is an unconnected piped writer, they may
     * be connected by either the call:
     * <blockquote><pre>
     * src.connect(snk)</pre></blockquote>
     * or the call:
     * <blockquote><pre>
     * snk.connect(src)</pre></blockquote>
     * The two calls have the same effect.
     *
     * @param snk the piped reader to connect to.
     *
     * @throws IOException if an I/O error occurs.
     */
    // 与指定的读管道建立连接
    public synchronized void connect(PipedReader snk) throws IOException {
        if(snk == null) {
            throw new NullPointerException();
        } else if(sink != null || snk.connected) {
            throw new IOException("Already connected");
        } else if(snk.closedByReader || closed) {
            throw new IOException("Pipe closed");
        }
        
        sink = snk;
        snk.in = -1;
        snk.out = 0;
        snk.connected = true;
    }
    
    /*▲ 交互 ████████████████████████████████████████████████████████████████████████████████┛ */
    
}