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public final class ReadWriteLock {
private int readingReaders = 0; // (A)...实际正在读取的执行绪数量
private int waitingWriters = 0; // (B)...正在等待写入的执行绪数量
private int writingWriters = 0; // (C)...实际正在写入的执行绪数量
private boolean preferWriter = true; // 写入优先的话,值为true
public synchronized void readLock() throws InterruptedException {
while (writingWriters > 0 || (preferWriter && waitingWriters > 0)) {
wait();
}
readingReaders++; // (A)实际正在读取的线程数量加1
}
public synchronized void readUnlock() {
readingReaders--; // (A)实际正在读取的线程数量减1
preferWriter = true;
notifyAll();
}
public synchronized void writeLock() throws InterruptedException {
waitingWriters++; // (B)正在等待写入的线程数量加1
try {
while (readingReaders > 0 || writingWriters > 0) {
wait();
}
} finally {1
waitingWriters--; // (B)正在等待写入的线程数量减1
}
writingWriters++; // (C)实际正在写入的线程数量加1
}
public synchronized void writeUnlock() {
writingWriters--; // (C)实际正在写入的线程数量减
preferWriter = false;
notifyAll();
}
}
// 数据类
public class Data {
private final char[] buffer;
private final ReadWriteLock lock = new ReadWriteLock();
public Data(int size) {
this.buffer = new char[size];
for (int i = 0; i < buffer.length; i++) {
buffer[i] = '*';
}
}
public char[] read() throws InterruptedException {
lock.readLock();
try {
return doRead();
} finally {
lock.readUnlock();
}
}
public void write(char c) throws InterruptedException {
lock.writeLock();
try {
doWrite(c);
} finally {
lock.writeUnlock();
}
}
private char[] doRead() {
char[] newbuf = new char[buffer.length];
for (int i = 0; i < buffer.length; i++) {
newbuf[i] = buffer[i];
}
slowly();
return newbuf;
}
private void doWrite(char c) {
for (int i = 0; i < buffer.length; i++) {
buffer[i] = c;
slowly();
}
}
private void slowly() {
try {
Thread.sleep(50);
} catch (InterruptedException e) {
}
}
}