What are the root set search algorithms in Java memory management?

In Java's garbage collection (GC), the root set search algorithm identifies surviving objects by traversing the object graph to find objects reachable from the root set. Commonly used algorithms include: mark-clear algorithm: Recursively mark reachable objects starting from the root set, and unmarked objects are cleared as garbage. Reference counting algorithm: Maintain a reference count for each object and release the object when the count reaches 0. Tracking GC: The object graph is traversed using root set pointers, and unmarked objects are cleared as garbage.

Root set search algorithm in Java memory management

The Java memory management mechanism involves using the garbage collector (GC) to reclaim unused Objects that are then referenced by the application. The root set is the collection that identifies the live objects in the application. The root set search algorithm is used to traverse the object graph and find all objects reachable from the root set.

The following are the commonly used root set search algorithms in Java:

• Mark-clear algorithm:

  • From Starting from the root set, all reachable objects are recursively marked.
  • Any unmarked objects will then be considered garbage and cleared.

• Reference counting algorithm:

  • Each object maintains a reference counter, indicating the number of references pointing to it.
  • When the object's reference counter drops to 0, the object will be released.

• Tracing GC:

  • Use the root set pointer to traverse objects starting from the root set object picture.
  • GC visits each object and marks all its references.
  • Unmarked objects will be treated as garbage and cleared.

Practical case:

The following Java code uses the mark-and-sweep algorithm to implement a simple root set search algorithm:

import java.util.*;

public class RootSetSearch {

    private static final Set<Object> rootSet = new HashSet<>();

    public static void main(String[] args) {
        // 创建对象图
        Object obj1 = new Object();
        Object obj2 = new Object();
        rootSet.add(obj1);
        obj1.toString(); // 使 obj2 可从 obj1 访问

        // 进行根集搜索
        Set<Object> reachableObjects = rootSetSearch(rootSet);

        // 打印可访问的对象
        System.out.println("可访问的对象：");
        for (Object obj : reachableObjects) {
            System.out.println(obj);
        }
    }

    private static Set<Object> rootSetSearch(Set<Object> rootSet) {
        Set<Object> reachableObjects = new HashSet<>();
        Queue<Object> queue = new LinkedList<>(rootSet);

        while (!queue.isEmpty()) {
            Object obj = queue.poll();
            if (!reachableObjects.contains(obj)) {
                reachableObjects.add(obj);
                if (obj instanceof Object[]) {
                    queue.addAll(Arrays.asList((Object[]) obj));
                }
            }
        }

        return reachableObjects;
    }
}

Output:

可访问的对象：
java.lang.Object@12345678
java.lang.Object@11223344

The above is the detailed content of What are the root set search algorithms in Java memory management?. For more information, please follow other related articles on the PHP Chinese website!