高级线程模式

Java 代码优化

Pavlos Kosmetatos

Lead Engineer @Wealthyhood

线程池基础

创建线程代价高！

线程池：

复用现有线程
控制并发线程数
通过 ExecutorService 接口管理

创建线程池

// Fixed thread pool with 4 threads
ExecutorService fixedPool = Executors.newFixedThreadPool(4);


// Cached thread pool that grows as needed
ExecutorService cachedPool = Executors.newCachedThreadPool();


// Single-threaded executor
ExecutorService singleExecutor = Executors.newSingleThreadExecutor();

提交任务

ExecutorService executor = Executors.newFixedThreadPool(4);

// Submit a task with no return value
executor.execute(() -> System.out.println("Simple task"));

// Submit a task with a return value (Callable)
Future<Integer> future = executor.submit(() -> {
    Thread.sleep(1000);
    return 42;
});

// Get result from Future (blocks until complete)
int result = future.get();

关闭执行器

// Signal shutdown, but continue running existing tasks
executor.shutdown();


// Wait for termination (with timeout)
boolean terminated = executor.awaitTermination(5, TimeUnit.SECONDS);


// Force immediate shutdown, canceling running tasks
executor.shutdownNow();

CompletableFuture 简介

CompletableFuture
自 Java 8 起属于并发 API
现代异步编程方式
可手动完成或通过 Function 完成
支持用回调链式操作
可与显式线程池配合或独立使用

创建 CompletableFuture

// Run async with default executor
CompletableFuture<Void> runAsync = 
    CompletableFuture.runAsync(() -> performTask());


// Supply async with custom executor
ExecutorService executor = Executors.newCachedThreadPool();
CompletableFuture<String> supplyAsync = 
    CompletableFuture.supplyAsync(() -> fetchData(), executor);

链式操作

CompletableFuture<String> future = CompletableFuture
    .supplyAsync(() -> fetchUserData(userId))
    .thenApply(data -> extractUsername(data))
    .exceptionally(ex -> "Unknown user");

// Access to result when ready
future.thenAccept(result -> System.out.println(result));

Vamos praticar!

Java 代码优化