PipedOutputStream.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 java.io;

/**
 * A piped output stream can be connected to a piped input stream
 * to create a communications pipe. The piped output stream is the
 * sending end of the pipe. Typically, data is written to a
 * <code>PipedOutputStream</code> object by one thread and data is
 * read from the connected <code>PipedInputStream</code> by some
 * other thread. Attempting to use both objects from a single thread
 * is not recommended as it may deadlock the thread.
 * The pipe is said to be <a id=BROKEN> <i>broken</i> </a> if a
 * thread that was reading data bytes from the connected piped input
 * stream is no longer alive.
 *
 * @author James Gosling
 * @see java.io.PipedInputStream
 * @since 1.0
 */
// (字节)写管道，需要与读管道配合使用
public class PipedOutputStream extends OutputStream {
    
    /*
     * 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 PipedInputStream sink;  // 连接的读管道
    
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Creates a piped output stream that is not yet connected to a
     * piped input stream. It must be connected to a piped input stream,
     * either by the receiver or the sender, before being used.
     *
     * @see java.io.PipedInputStream#connect(java.io.PipedOutputStream)
     * @see java.io.PipedOutputStream#connect(java.io.PipedInputStream)
     */
    // 构造写管道，未与读管道建立连接
    public PipedOutputStream() {
    }
    
    /**
     * Creates a piped output stream connected to the specified piped
     * input stream. Data bytes written to this stream will then be
     * available as input from <code>snk</code>.
     *
     * @param snk The piped input stream 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 PipedOutputStream(PipedInputStream snk) throws IOException {
        connect(snk);
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 写 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Writes the specified <code>byte</code> to the piped output stream.
     * <p>
     * Implements the <code>write</code> method of <code>OutputStream</code>.
     *
     * @param b the <code>byte</code> to be written.
     *
     * @throws IOException if the pipe is <a href=#BROKEN> broken</a>,
     *                     {@link #connect(java.io.PipedInputStream) unconnected},
     *                     closed, or if an I/O error occurs.
     */
    // 向读管道存入一个字节
    public void write(int b) throws IOException {
        if(sink == null) {
            throw new IOException("Pipe not connected");
        }
        
        // 将写入的字节保存到读管道的缓冲区
        sink.receive(b);
    }
    
    /**
     * Writes <code>len</code> bytes from the specified byte array
     * starting at offset <code>off</code> to this piped output stream.
     * This method blocks until all the bytes are written to the output
     * stream.
     *
     * @param b   the data.
     * @param off the start offset in the data.
     * @param len the number of bytes to write.
     *
     * @throws IOException if the pipe is <a href=#BROKEN> broken</a>,
     *                     {@link #connect(java.io.PipedInputStream) unconnected},
     *                     closed, or if an I/O error occurs.
     */
    // 向读管道存入字节数组b中off处起的len个字节
    public void write(byte[] b, int off, int len) throws IOException {
        if(sink == null) {
            throw new IOException("Pipe not connected");
        } else if(b == null) {
            throw new NullPointerException();
        } else if((off<0) || (off>b.length) || (len<0) || ((off + len)>b.length) || ((off + len)<0)) {
            throw new IndexOutOfBoundsException();
        } else if(len == 0) {
            return;
        }
        
        // 将写入的字节保存到读管道的缓冲区
        sink.receive(b, 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 bytes.
     *
     * @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 {
        if(sink != null) {
            sink.receivedLast();
        }
    }
    
    /**
     * Flushes this output stream and forces any buffered output bytes
     * to be written out.
     * This will notify any readers that bytes are waiting in the pipe.
     *
     * @throws IOException if 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) {
            synchronized(sink) {
                sink.notifyAll();
            }
        }
    }
    
    /*▲ 杂项 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 交互 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    /**
     * Connects this piped output stream to a receiver. If this object
     * is already connected to some other piped input stream, an
     * <code>IOException</code> is thrown.
     * <p>
     * If <code>snk</code> is an unconnected piped input stream and
     * <code>src</code> is an unconnected piped output stream, 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 input stream 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(PipedInputStream snk) throws IOException {
        if(snk == null) {
            throw new NullPointerException();
        } else if(sink != null || snk.connected) {
            throw new IOException("Already connected");
        }
        
        sink = snk;
        snk.in = -1;
        snk.out = 0;
        snk.connected = true;
    }
    
    /*▲ 交互 ████████████████████████████████████████████████████████████████████████████████┛ */
    
}