Java 多线程六：容器

发布时间：2023-04-17 11:40:36 所属栏目：教程来源：

导读：这两个都加了锁，一般不推荐使用。

ConcurrentHashMap
ConcurrentHashMap 写效率未必比 HashMap，HashTable 高，但是读效率比这两者要高。

示例代码：

package git.snippets.juc;
import java.util.*;
i

这两个都加了锁，一般不推荐使用。

ConcurrentHashMap
ConcurrentHashMap 写效率未必比 HashMap，HashTable 高，但是读效率比这两者要高。

示例代码：

package git.snippets.juc;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
/**
* ConcurrentHashMap写效率未必比HashMap，HashTable高，但是读效率比这两者要高
*/
public class HashTableVSCHM {
public static final int COUNT = 1000000;
public static final int THREAD_COUNT = 100;
static UUID[] keys = new UUID[COUNT];
static UUID[] values = new UUID[COUNT];
static {
for (int i = 0; i < COUNT; i++) {
keys[i] = UUID.randomUUID();
values[i] = UUID.randomUUID();
}
}
enum TYPE {
HASHTABLE, CHM, HASHMAP
}
public static Map<UUID, UUID> choose(TYPE type) {
switch (type) {
case HASHMAP:
Collections.synchronizedMap(new HashMap<>());
case HASHTABLE:
return new Hashtable<>();
default:
return new ConcurrentHashMap<>();
}
}
public static void main(String[] args) {
System.out.println("...use hashtable....");
benchmark(choose(TYPE.HASHTABLE));
System.out.println("...use HashMap....");
benchmark(choose(TYPE.HASHMAP));
System.out.println("...use ConcurrentHashMap....");
benchmark(choose(TYPE.CHM));
}
public static void benchmark(Map<UUID, UUID> hashtable) {
long start = System.currentTimeMillis();
Thread[] threads = new Thread[THREAD_COUNT];
for (int i = 0; i < threads.length; i++) {
threads[i] = new MyThread(i * COUNT / THREAD_COUNT, hashtable);
}
Arrays.stream(threads).forEach(thread -> thread.start());
Arrays.stream(threads).forEach(thread -> {
try {
thread.join();
} catch (InterruptedException e) {
e.printstacktrace();
}
});
long end = System.currentTimeMillis();
System.out.println("size : " + hashtable.size());
System.out.println("write cost " + (end - start) + "ms");
start = System.currentTimeMillis();
for (int i = 0; i < threads.length; i++) {
threads[i] = new Thread(() -> {
for (int j = 0; j < 10000000; j++) {
hashtable.get(keys[10]);
}
});
}
Arrays.stream(threads).forEach(thread -> thread.start());
Arrays.stream(threads).forEach(thread -> {
try {
thread.join();
} catch (InterruptedException e) {
e.printstacktrace();
}
});
end = System.currentTimeMillis();
System.out.println("read cost " + (end - start) + "ms");
}
static class MyThread extends Thread {
int start;
int gap = COUNT / THREAD_COUNT;
Map<UUID, UUID> map;
MyThread(int start, Map<UUID, UUID> map) {
this.start = start;
this.map = map;
}
@Override
public void run() {
for (int i = start; i < start + gap; i++) {
map.put(keys[i], values[i]);
}
}
}
}

（编辑：汽车网）

【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容!