我想知道这两种在 Java 7 中使用多线程执行任务的方法之间是否有任何区别:
简要要求 - 我必须同时处理 200 条记录,并且每条记录只能处理一次。
方法一:
public class Counter {
private static int count = -1;
private static final Object lock = new Object();
public static int getCount() {
synchronized (lock) {
return ++count;
}
}
}
public class Task implements Runnable {
@Override
public void run() {
int count = 0;
while((count = Counter.getCount()) < 200) {
System.out.println(Thread.currentThread().getName() + " " + count);
// process record # count
}
}
}
public class Tester {
public static void main(String[] args) throws InterruptedException {
long start = System.currentTimeMillis();
ExecutorService service = Executors.newFixedThreadPool(10);
for (int i = 0; i < 10; i++) {
service.execute(new Task());
}
service.shutdown();
service.awaitTermination(5, TimeUnit.MINUTES);
long end = System.currentTimeMillis();
System.out.println(end - start);
}
}
方法 2:
public class Task2 implements Runnable {
private int i = 0;
public Task2(int i) {
super();
this.i = i;
}
@Override
public void run() {
System.out.println(Thread.currentThread().getName() + " " + i);
// process record # i
}
}
public class Tester2 {
public static void main(String[] args) throws InterruptedException {
long start = System.currentTimeMillis();
ExecutorService service = Executors.newFixedThreadPool(10);
for (int i = 0; i < 200; i++) {
service.execute(new Task2(i));
}
service.shutdown();
service.awaitTermination(5, TimeUnit.MINUTES);
long end = System.currentTimeMillis();
System.out.println(end - start);
}
}
两者都运行良好并产生相同的输出并且花费几乎相同的时间。 然而,示例代码中的 200 个数字在实际场景中将达到数十亿。请建议哪一个在内存和CPU等方面更好。
谢谢。
编辑 - 根据 Jimmy T. 的建议添加方法 3。
方法 3:
public class Tester3 {
public static void main(String[] args) throws InterruptedException {
int processedRecords = 0;
int totalRecords = 200;
int recordsPerThread = 10;
boolean continueProcess = true;
ExecutorService service = Executors.newFixedThreadPool(10);
while(continueProcess) {
int startIndex = processedRecords;
int endIndex = startIndex + recordsPerThread - 1;
if (endIndex >= totalRecords - 1) {
endIndex = totalRecords - 1;
continueProcess = false;
}
processedRecords = processedRecords + recordsPerThread;
service.submit(new Task3(startIndex, endIndex));
}
service.shutdown();
service.awaitTermination(5, TimeUnit.MINUTES);
}
}
public class Task3 implements Runnable {
private int startIndex = 0;
private int endIndex = 0;
public Task3(int startIndex, int endIndex) {
super();
this.startIndex = startIndex;
this.endIndex = endIndex;
}
@Override
public void run() {
System.out.println("processing records from " + startIndex + " to " + endIndex);
}
}
最佳答案
Brief requirement - I have to process 200 records, simultaneously, and each record should be processed once only.
However 200 number taken in example code will be in billions in actual scenario.
一如既往,答案是“视情况而定”。除非您的任务非常快,否则同步或对象创建的开销应该不重要。请注意,ExecutorService
也必须在内部进行一些同步。
您可以使用 AtomicInteger
计数器来避免同步并简化代码。但我很可能会选择一个 Queue 和几个 Runnable 来轮询它,因为它很简单并且为您提供了很大的灵活性:
- 如果您想确定某些记录的优先级,可以使用
PriorityQueue
- 如果将所有记录存储在内存中成本太高,您可以创建自己的队列(您的队列可以从文件或数据库或其他任何地方获取它们)
您可以预先填充队列或使用由生产者填充的BlockingQueue
。队列的内容可以是记录索引或(可能更好)记录本身。
每个任务都会轮询队列并在队列为空时终止。
public class Task3 implements Runnable {
@Override public void run() {
while (true) {
final Integer i = queue.poll();
if (i==null) break;
System.out.println(Thread.currentThread().getName() + " " + i);
// process record # i
}
}
}
您只需创建有限数量的它们即可让您的所有核心保持忙碌。
ExecutorService service = Executors.newFixedThreadPool(10);
for (int i = 0; i < 10; i++) service.execute(new Task3());
关于java - 哪种方法更好 - 多线程示例,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/25534751/