读者写者问题中在读者优先其算法的时间复杂性
时间: 2023-06-07 08:11:27 浏览: 38
通常为O(1),而在写者优先情况下,时间复杂性为O(n),其中n是读者的数量。这是因为在读者优先情况下,写者必须等待所有读者完成它们的读取操作后才能再次获得对共享资源的访问权。相反,当写者优先时,所有等待的读者必须等待当前运行的写者完成其操作,才能获得对共享资源的访问权。这可能导致读者被阻塞并且需要等待的时间更长。
相关问题
Java实现读者-写者问题的写者优先算法
Java实现读者-写者问题的写者优先算法可以通过使用ReentrantReadWriteLock类来实现。该类提供了读写锁定的机制,其中读锁定可以被多个线程同时持有,而写锁定只能被单个线程持有。
下面是一个示例代码,实现了读者-写者问题的写者优先算法:
```
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class WriterPriorityReadWriteLock {
private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
private final ReentrantReadWriteLock.WriteLock writeLock = lock.writeLock();
private final ReentrantReadWriteLock.ReadLock readLock = lock.readLock();
private int readers = 0;
private int writers = 0;
private int writeRequests = 0;
public void startRead() throws InterruptedException {
readLock.lock();
try {
while (writers > 0 || writeRequests > 0) {
wait();
}
readers++;
} finally {
readLock.unlock();
}
}
public void endRead() {
readLock.lock();
try {
readers--;
notifyAll();
} finally {
readLock.unlock();
}
}
public void startWrite() throws InterruptedException {
writeLock.lock();
try {
writeRequests++;
while (readers > 0 || writers > 0) {
wait();
}
writeRequests--;
writers++;
} finally {
writeLock.unlock();
}
}
public void endWrite() {
writeLock.lock();
try {
writers--;
notifyAll();
} finally {
writeLock.unlock();
}
}
}
```
在这个实现中,读者和写者线程都可以通过调用startRead()和startWrite()方法来获取锁定,然后通过调用endRead()和endWrite()方法来释放锁定。在写者优先算法中,如果存在等待的写者,则新的读者线程必须等待所有等待的写者完成。
需要注意的是,如果有多个写者在等待锁定,则它们将按照先来先服务的顺序获得锁定。因此,这种实现可能会导致饥饿现象,即某些线程可能会无限期地等待。为了避免这种情况,可以采用其他的算法,例如读者优先算法或者公平算法。
读者-写者问题的写者优先算法全部代码
下面是完整的Java实现读者-写者问题的写者优先算法:
```
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class WriterPriorityReadWriteLock {
private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
private final ReentrantReadWriteLock.WriteLock writeLock = lock.writeLock();
private final ReentrantReadWriteLock.ReadLock readLock = lock.readLock();
private int readers = 0;
private int writers = 0;
private int writeRequests = 0;
public void startRead() throws InterruptedException {
readLock.lock();
try {
while (writers > 0 || writeRequests > 0) {
wait();
}
readers++;
} finally {
readLock.unlock();
}
}
public void endRead() {
readLock.lock();
try {
readers--;
notifyAll();
} finally {
readLock.unlock();
}
}
public void startWrite() throws InterruptedException {
writeLock.lock();
try {
writeRequests++;
while (readers > 0 || writers > 0) {
wait();
}
writeRequests--;
writers++;
} finally {
writeLock.unlock();
}
}
public void endWrite() {
writeLock.lock();
try {
writers--;
notifyAll();
} finally {
writeLock.unlock();
}
}
}
```
在这个实现中,读者和写者线程都可以通过调用startRead()和startWrite()方法来获取锁定,然后通过调用endRead()和endWrite()方法来释放锁定。在写者优先算法中,如果存在等待的写者,则新的读者线程必须等待所有等待的写者完成。
需要注意的是,如果有多个写者在等待锁定,则它们将按照先来先服务的顺序获得锁定。因此,这种实现可能会导致饥饿现象,即某些线程可能会无限期地等待。为了避免这种情况,可以采用其他的算法,例如读者优先算法或者公平算法。