Avancerade trådmönster

Optimera kod i Java

Pavlos Kosmetatos

Lead Engineer @Wealthyhood

Grunderna i trådpooler

Att skapa trådar är dyrt!

Trådpooler:

Återanvänder befintliga trådar
Begränsar antalet parallella trådar
Hanteras via gränssnittet ExecutorService

Skapa trådpooler

// 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();

Skicka in uppgifter

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();

Stänga ner executors

// 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

CompletableFuture
Del av Javas concurrency-API sedan Java 8
Modernt sätt att hantera asynkron programmering
Kan slutföras manuellt eller via en Function
Möjliggör kedjeoperationer med callbacks
Fungerar med eller utan explicita trådpooler

Skapa completable futures

// 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);

Kedja operationer

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));

Nu kör vi en övning!

Optimera kod i Java