多线程 Java 程序中如何使用锁？
锁可能是比标准同步块更灵活和复杂的线程同步机制。锁可以是用于控制多个线程对共享资源的访问的工具。通常，锁提供对共享资源的独占访问:一次只有一个线程可以获取锁，每个访问共享资源的人都需要先获取锁。然而，有些锁可能允许对共享资源的并发访问，比如读写锁的读锁。
// Example of lock interface
Lock lock = new ReentrantLock();
lock.lock();
// critical section
lock.unlock();
锁定界面中的方法
锁接口中有某些方法。我们将查看那些以及它们的修饰符:
–它试图立即累积锁，如果锁定成功则返回 true | **[modifier]** | **Description** | | --- | --- | | 空的 | Lock ()–If the lock is available, it will acquire the lock; If the lock is not available, the thread will be blocked until the lock is released. | | Lock Intermittent ()–It is similar to lock (), but it will acquire the lock unless the thread is interrupted. | | Unlock ()–as the name implies, it is just an instance of releasing the lock. | | condition | New condition ()–It just returns a new condition instance. | | boolean type | | TryLock (time unit unit)–it is usually almost the same as try Lock (), except that it waits for a given timeout before giving up trying to accumulate locks. |锁的实施
让我们看看如何在 Java 中实现一些锁:
ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
readWriteLock.readLock().lock();
// ....
......//
readWriteLock.readLock().unlock();
readWriteLock.writeLock().lock();
// only one writer can enter this section,
// and only if no threads are currently reading.
readWriteLock.writeLock().unlock();
下面是 readWriteLock()方法的实现:
T3】JavaT5
// Implementation of ReadWriteLock in Java
import java.io.*;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
class GFG<O> {
private final ReadWriteLock readWriteLock
= new ReentrantReadWriteLock();
private final Lock writeLock
= readWriteLock.writeLock();
private final Lock readLock = readWriteLock.readLock();
private final List<O> list = new ArrayList<>();
// setElement function sets
// i.e., write the element to the thread
public void setElement(O o)
{
// acquire the thread for writing
writeLock.lock();
try {
list.add(o);
System.out.println(
"Element by thread "
+ Thread.currentThread().getName()
+ " is added");
}
finally {
// To unlock the acquired write thread
writeLock.unlock();
}
}
// getElement function prints
// i.e., read the element from the thread
public O getElement(int i)
{
// acquire the thread for reading
readLock.lock();
try {
System.out.println(
"Elements by thread "
+ Thread.currentThread().getName()
+ " is printed");
return list.get(i);
}
finally {
// To unlock the acquired read thread
readLock.unlock();
}
}
public static void main(String[] args)
{
GFG<String> gfg = new GFG<>();
gfg.setElement("Hi");
gfg.setElement("Hey");
gfg.setElement("Hello");
System.out.println("Printing the last element : "
+ gfg.getElement(2));
}
}
T6T8输出T1
public class lockImplement {
//...
ReentrantLock lock = new ReentrantLock();
int counter = 0;
public void testing() {
lock.lock();
try {
// Critical section here
count++;
} finally {
lock.unlock();
}
}
//...
}
下面是重入锁()方法的实现:
Java
T0T6】
输出:
task name - Job2 waiting for lock
task name - Job1 outer lock acquired at 09:49:42 Doing outer work
task name - Job2 waiting for lock
task name - Job1 inner lock acquired at 09:49:44 Doing inner work
Lock Hold Count - 2
task name - Job2 waiting for lock
task name - Job2 waiting for lock
task name - Job1 releasing inner lock
Lock Hold Count - 1
task name - Job1 work done
task name - Job1 releasing outer lock
Lock Hold Count - 0
task name - Job3 outer lock acquired at 09:49:45 Doing outer work
task name - Job2 waiting for lock
task name - Job3 inner lock acquired at 09:49:47 Doing inner work
Lock Hold Count - 2
task name - Job2 waiting for lock
task name - Job2 waiting for lock
task name - Job3 releasing inner lock
Lock Hold Count - 1
task name - Job3 work done
task name - Job3 releasing outer lock
Lock Hold Count - 0
task name - Job4 outer lock acquired at 09:49:48 Doing outer work
task name - Job2 waiting for lock
task name - Job4 inner lock acquired at 09:49:50 Doing inner work
Lock Hold Count - 2
task name - Job2 waiting for lock
task name - Job2 waiting for lock
task name - Job4 releasing inner lock
Lock Hold Count - 1
task name - Job4 work done
task name - Job4 releasing outer lock
Lock Hold Count - 0
task name - Job2 outer lock acquired at 09:49:52 Doing outer work
task name - Job2 inner lock acquired at 09:49:53 Doing inner work
Lock Hold Count - 2
task name - Job2 releasing inner lock
Lock Hold Count - 1
task name - Job2 work done
task name - Job2 releasing outer lock
Lock Hold Count - 0
注意:由于睡眠调用，程序可能无法在在线 IDE 上工作。
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