The principles and implementation behind Java concurrent collections

ConcurrencyCollectionsOverview

The "Principles and Implementation Behind Java Concurrent Collections" launched by php editor Yuzai deeply explores the principles, implementation methods and usage of Java concurrent collection classes. Through this topic, readers will have a comprehensive understanding of the mechanisms behind various concurrent collections in Java, providing an important reference for solving security and efficiency issues when multi-threads access data concurrently.

CopyOnWriteArrayList

CopyOnWriteArrayList is a thread-safe ArrayList implementation that uses the copy-on-write strategy to ensure thread safety. In the copy-on-write strategy, when a thread attempts to modify CopyOnWriteArrayList, a new ArrayList instance is created and the elements in the original collection are copied to the new instance. Then, modifications are made to the new instance, leaving the original collection unchanged. This strategy ensures that modifications to CopyOnWriteArrayList are atomic in a multi-threaded environment and will not cause data inconsistency.

Demo code:

import java.util.concurrent.CopyOnWriteArrayList;

public class CopyOnWriteArrayListExample {

public static void main(String[] args) {
CopyOnWriteArrayList<String> list = new CopyOnWriteArrayList<>();
list.add("Item 1");
list.add("Item 2");
list.add("Item 3");

// 创建一个新的线程并尝试修改 list
Thread thread = new Thread(() -> {
list.add("Item 4");
});
thread.start();

// 主线程继续对 list 进行修改
list.add("Item 5");

// 打印最终的 list
System.out.println(list);
}
}

Output result:

import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashMapExample {

public static void main(String[] args) {
ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
map.put("Item 1", 1);
map.put("Item 2", 2);
map.put("Item 3", 3);

// 创建一个新的线程并尝试修改 map
Thread thread = new Thread(() -> {
map.put("Item 4", 4);
});
thread.start();

// 主线程继续对 map 进行修改
map.put("Item 5", 5);

// 打印最终的 map
System.out.println(map);
}
}

Output result:

import java.util.concurrent.ConcurrentLinkedQueue;

public class ConcurrentLinkedQueueExample {

public static void main(String[] args) {
ConcurrentLinkedQueue<String> queue = new ConcurrentLinkedQueue<>();
queue.add("Item 1");
queue.add("Item 2");
queue.add("Item 3");

// 创建一个新的线程并尝试修改 queue
Thread thread = new Thread(() -> {
queue.add("Item 4");
});
thread.start();

// 主线程继续对 queue 进行修改
queue.add("Item 5");

// 打印最终的 queue
System.out.println(queue);
}
}

Output result:

[Item 1, Item 2, Item 3, Item 5, Item 4]

In this example, the main thread and the new thread modify the queue at the same time, but because ConcurrentLinkedQueue uses the CAS operation strategy, the modifications of the two threads are atomic and will not cause data inconsistency.

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