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PipedWriter和PipedReader源码分析
1. PipedWriter 源码(基于jdk1.7.40)
package java.io;
public class PipedWriter extends Writer {
// 与PipedWriter通信的PipedReader对象
private PipedReader sink;
// PipedWriter的关闭标记
private boolean closed = false;
// 构造函数，指定配对的PipedReader
public PipedWriter(PipedReader snk) throws IOException {
connect(snk);
}
// 构造函数
public PipedWriter() {
}
// 将“PipedWriter” 和 “PipedReader”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;
// 设置“PipedReader”和“PipedWriter”为已连接状态
// connected是PipedReader中定义的，用于表示“PipedReader和PipedWriter”是否已经连接
snk.connected = true;
}
// 将一个字符c写入“PipedWriter”中。
// 将c写入“PipedWriter”之后，它会将c传输给“PipedReader”
public void write(int c) throws IOException {
if (sink == null) {
throw new IOException("Pipe not connected");
}
sink.receive(c);
}
// 将字符数组b写入“PipedWriter”中。
// 将数组b写入“PipedWriter”之后，它会将其传输给“PipedReader”
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))) < ) {
throw new IndexOutOfBoundsException();
}
sink.receive(cbuf, off, len);
}
// 清空“PipedWriter”。
// 这里会调用“PipedReader”的notifyAll()；
// 目的是让“PipedReader”放弃对当前资源的占有，让其它的等待线程(等待读取PipedWriter的线程)读取“PipedWriter”的值。
public synchronized void flush() throws IOException {
if (sink != null) {
if (sink.closedByReader || closed) {
throw new IOException("Pipe closed");
}
synchronized (sink) {
sink.notifyAll();
}
}
}
// 关闭“PipedWriter”。
// 关闭之后，会调用receivedLast()通知“PipedReader”它已经关闭。
public void close() throws IOException {
closed = true;
if (sink != null) {
sink.receivedLast();
}
}
}
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2. PipedReader 源码(基于jdk1.7.40)
package java.io;
public class PipedReader extends Reader {
// “PipedWriter”是否关闭的标记
boolean closedByWriter = false;
// “PipedReader”是否关闭的标记
boolean closedByReader = false;
// “PipedReader”与“PipedWriter”是否连接的标记
// 它在PipedWriter的connect()连接函数中被设置为true
boolean connected = false;
Thread readSide; // 读取“管道”数据的线程
Thread writeSide; // 向“管道”写入数据的线程
// “管道”的默认大小
private static final int DEFAULT_PIPE_SIZE = 1024;
// 缓冲区
char buffer[];
//下一个写入字符的位置。in==out代表满，说明“写入的数据”全部被读取了。
int in = -;
//下一个读取字符的位置。in==out代表满，说明“写入的数据”全部被读取了。
int out = ;
// 构造函数：指定与“PipedReader”关联的“PipedWriter”
public PipedReader(PipedWriter src) throws IOException {
this(src, DEFAULT_PIPE_SIZE);
}
// 构造函数：指定与“PipedReader”关联的“PipedWriter”，以及“缓冲区大小”
public PipedReader(PipedWriter src, int pipeSize) throws IOException {
initPipe(pipeSize);
connect(src);
}
// 构造函数：默认缓冲区大小是1024字符
public PipedReader() {
initPipe(DEFAULT_PIPE_SIZE);
}
// 构造函数：指定缓冲区大小是pipeSize
public PipedReader(int pipeSize) {
initPipe(pipeSize);
}
// 初始化“管道”：新建缓冲区大小
private void initPipe(int pipeSize) {
if (pipeSize <= 0) {
throw new IllegalArgumentException("Pipe size <= 0");
}
buffer = new char[pipeSize];
}
// 将“PipedReader”和“PipedWriter”绑定。
// 实际上，这里调用的是PipedWriter的connect()函数
public void connect(PipedWriter src) throws IOException {
src.connect(this);
}
// 接收int类型的数据b。
// 它只会在PipedWriter的write(int b)中会被调用
synchronized void receive(int c) throws IOException {
// 检查管道状态
if (!connected) {
throw new IOException("Pipe not connected");
} else if (closedByWriter || closedByReader) {
throw new IOException("Pipe closed");
} else if (readSide != null && !readSide.isAlive()) {
throw new IOException("Read end dead");
}
// 获取“写入管道”的线程
writeSide = Thread.currentThread();
// 如果“管道中被读取的数据，等于写入管道的数据”时，
// 则每隔1000ms检查“管道状态”，并唤醒管道操作：若有“读取管道数据线程被阻塞”，则唤醒该线程。
while (in == out) {
if ((readSide != null) && !readSide.isAlive()) {
throw new IOException("Pipe broken");
}
/* full: kick any waiting readers */
notifyAll();
try {
wait(1000);
} catch (InterruptedException ex) {
throw new java.io.InterruptedIOException();
}
}
if (in < 0) {
in = 0;
out = 0;
}
buffer[in++] = (char) c;
if (in >= buffer.length) {
in = 0;
}
}
// 接收字符数组b。
synchronized void receive(char c[], int off, int len) throws IOException {
while (--len >= ) {
receive(c[off++]);
}
}
// 当PipedWriter被关闭时，被调用
synchronized void receivedLast() {
closedByWriter = true;
notifyAll();
}
// 从管道(的缓冲)中读取一个字符，并将其转换成int类型
public synchronized int read() throws IOException {
if (!connected) {
throw new IOException("Pipe not connected");
} else if (closedByReader) {
throw new IOException("Pipe closed");
} else if (writeSide != null && !writeSide.isAlive()
&& !closedByWriter && (in < )) {
throw new IOException("Write end dead");
}
readSide = Thread.currentThread();
int trials = 2;
while (in < 0) {
if (closedByWriter) {
/* closed by writer, return EOF */
return -1;
}
if ((writeSide != null) && (!writeSide.isAlive()) && (--trials < )) {
throw new IOException("Pipe broken");
}
/* might be a writer waiting */
notifyAll();
try {
wait(1000);
} catch (InterruptedException ex) {
throw new java.io.InterruptedIOException();
}
}
int ret = buffer[out++];
if (out >= buffer.length) {
out = 0;
}
if (in == out) {
/* now empty */
in = -1;
}
return ret;
}
// 从管道(的缓冲)中读取数据，并将其存入到数组b中
public synchronized int read(char cbuf[], int off, int len) throws IOException {
if (!connected) {
throw new IOException("Pipe not connected");
} else if (closedByReader) {
throw new IOException("Pipe closed");
} else if (writeSide != null && !writeSide.isAlive()
&& !closedByWriter && (in < 0)) {
throw new IOException("Write end dead");
}
if ((off < 0) || (off > cbuf.length) || (len < 0) ||
((off + len) > cbuf.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
}
/* possibly wait on the first character */