在executor框架中同步资源
在executor框架中同步资源
提问于 2015-03-24 03:28:24
我正在使用executor框架来执行一个大型任务。出于进程状态的目的，我需要对已完成的数量进行计数。所以我创建了一个带有计数器的单例类来保持计数。
public class ProgramInitializationTracker {
private static Map<String, Integer> programInitializedTracker = new HashMap<>();
private static ProgramInitializationTracker instance;
private ProgramInitializationTracker(){
}
public static ProgramInitializationTracker getInstance(){
if(instance == null){
synchronized (ProgramInitializationTracker.class) {
if(instance == null){
instance = new ProgramInitializationTracker();
}
}
}
return instance;
}
public Integer getProgramInitializedTracker(String key) {
return programInitializedTracker.get(key);
}
public void setProgramInitializedTracker(String key, int value) {
synchronized (ProgramInitializationTracker.class) {
ProgramInitializationTracker.programInitializedTracker.put(key, value);
}
}
}但问题是，仅仅通过同步set方法并不能真正确保我有正确的count值。就我所能得到的多线程而言。让get函数也同步会对我有帮助。如果不是，那么我应该做些什么来纠正它。
回答 2
Stack Overflow用户
发布于 2015-03-24 03:51:19
当Java已经为您提供了对集合的线程安全访问时，您不应该尝试实现您自己的线程安全访问。
您应该使用ConcurrentHashMap。诸如get之类的读取不会阻塞。
但是，您应该使用AtomicInteger，而不是使用Integer类型作为存储在映射中的值，这将确保尝试修改与相同键关联的值的多个线程是线程安全的。
Stack Overflow用户
发布于 2015-03-24 04:47:31
在你发布的约束下，只需在你提交给ExecutorService的任务和你想要有指标的地方之间共享一个AtomicInteger实例即可。variant1用于具有覆盖所有任务的单个计数器，而variant2用于针对每个任务类型具有计数器。这段代码是(应该是)线程安全的。
@ThreadSafe
class Test {
private static class CountingRunnable implements Runnable {
@Nonnull
private final Runnable actualTask;
@Nonnull
private final AtomicInteger submitted;
public CountingRunnable(@Nonnull Runnable actualTask, @Nonnull AtomicInteger submitted) {
this.actualTask = actualTask;
this.submitted = submitted;
}
@Override
public void run() {
actualTask.run();
submitted.incrementAndGet();
}
}
public static void main(String[] args) throws InterruptedException {
variant2();
}
private static void variant1() throws InterruptedException {
ExecutorService service = Executors.newFixedThreadPool(2);
AtomicInteger counter = new AtomicInteger();
final CountDownLatch latch = new CountDownLatch(1);
service.submit(new CountingRunnable(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
latch.countDown();
} catch (InterruptedException e) {}
}
}, counter));
latch.await();
System.out.println(counter.get());
service.shutdown();
}
private enum TaskType {
TYPE_1,
TYPE_2
}
private static void variant2() throws InterruptedException {
ExecutorService service = Executors.newFixedThreadPool(2);
final CountDownLatch latch = new CountDownLatch(2);
final EnumMap<TaskType, AtomicInteger> metrics = new EnumMap<>(TaskType.class);
metrics.put(TaskType.TYPE_1, new AtomicInteger());
metrics.put(TaskType.TYPE_2, new AtomicInteger());
service.submit(new CountingRunnable(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
latch.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, metrics.get(TaskType.TYPE_1)));
service.submit(new CountingRunnable(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
latch.countDown();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, metrics.get(TaskType.TYPE_2)));
latch.await();
System.out.println("type 1: " + metrics.get(TaskType.TYPE_1));
System.out.println("type 2: " + metrics.get(TaskType.TYPE_2));
service.shutdown();
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/29218739
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