In the world of software development, effectively managing resource consumption and ensuring fair usage of services are important considerations in building scalable and robust applications. Throttling is the practice of controlling the rate at which certain operations are performed and is a key mechanism to achieve these goals. In this article, we will take a deep dive into the various ways to implement throttling in Java and introduce various strategies with practical examples.

Explore limitations in Java

Exploring Limitations in Java: Simple Implementation Example - Part 1

Manage Resource Consumption Efficiently and ensuring fair usage of services are important considerations in building scalable and robust applications.

In the world of software development, effectively managing resource consumption and ensuring fair usage of services are important considerations in building scalable and robust applications. Throttling is the practice of controlling the rate at which certain operations are performed and is a key mechanism to achieve these goals. In this article, we’ll take a deep dive into the various ways to implement throttling in Java and introduce various strategies with practical examples.

Disclaimer: In this article, I will focus on simple single-threaded illustrations solving basic solutions.

Understanding Limits

Limits involve regulating how often certain operations are allowed to occur. This is particularly important in situations where the system needs to be protected against abuse, requires resource management, or requires fair access to shared services. Common use cases for throttling include limiting the rate of API requests, managing data updates, and controlling access to critical resources.

Simple blocking rate limiter - not for production use! thread.sleep()

A simple way to implement throttling is to use this method to introduce a delay between successive operations. Although this method is simple, it may not be suitable for high-performance scenarios due to its blocking nature. Thread.sleep()

public class SimpleRateLimiter {

    private long lastExecutionTime = 0;
    private long intervalInMillis;

    public SimpleRateLimiter(long requestsPerSecond) {
        this.intervalInMillis = 1000 / requestsPerSecond;
    }

    public void throttle() throws InterruptedException {
        long currentTime = System.currentTimeMillis();
        long elapsedTime = currentTime - lastExecutionTime;

        if (elapsedTime < intervalInMillis) {
            Thread.sleep(intervalInMillis - elapsedTime);
        }

        lastExecutionTime = System.currentTimeMillis();
        // Perform the throttled operation
        System.out.println("Throttled operation executed at: " + lastExecutionTime);
    }
}

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In this example, this class allows a specified number of operations to be performed per second. If the time elapsed between operations is less than the configured interval, a sleep duration is introduced to achieve the desired rate. SimpleRateLimiter

Basic Limitation of Wait

Let's start with a simple example that we use to limit the execution of a method. The goal is to allow the method to be called only after a specific cooldown time has elapsed. wait

public class BasicThrottling {

    private final Object lock = new Object();
    private long lastExecutionTime = 0;
    private final long cooldownMillis = 5000; // 5 seconds cooldown

    public void throttledOperation() throws InterruptedException {
        synchronized (lock) {
            long currentTime = System.currentTimeMillis();
            long elapsedTime = currentTime - lastExecutionTime;

            if (elapsedTime < cooldownMillis) {
                lock.wait(cooldownMillis - elapsedTime);
            }

            lastExecutionTime = System.currentTimeMillis();
            // Perform the throttled operation
            System.out.println("Throttled operation executed at: " + lastExecutionTime);
        }
    }
}

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In this example, the method uses this method to make the thread wait for the cooldown period to elapse. throttledOperationwait

Dynamic Limiting with Waits and Notifications

Let's enhance the previous example to introduce dynamic throttling, where the cooldown can be adjusted dynamically. Production must have the opportunity to make changes on the fly.

public class DynamicThrottling {

    private final Object lock = new Object();
    private long lastExecutionTime = 0;
    private long cooldownMillis = 5000; // Initial cooldown: 5 seconds

    public void throttledOperation() throws InterruptedException {
        synchronized (lock) {
            long currentTime = System.currentTimeMillis();
            long elapsedTime = currentTime - lastExecutionTime;

            if (elapsedTime < cooldownMillis) {
                lock.wait(cooldownMillis - elapsedTime);
            }

            lastExecutionTime = System.currentTimeMillis();
            // Perform the throttled operation
            System.out.println("Throttled operation executed at: " + lastExecutionTime);
        }
    }

    public void setCooldown(long cooldownMillis) {
        synchronized (lock) {
            this.cooldownMillis = cooldownMillis;
            lock.notify(); // Notify waiting threads that cooldown has changed
        }
    }

    public static void main(String[] args) {
        DynamicThrottling throttling = new DynamicThrottling();

        for (int i = 0; i < 10; i++) {
            try {
                throttling.throttledOperation();
                // Adjust cooldown dynamically
                throttling.setCooldown((i + 1) * 1000); // Cooldown increases each iteration
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

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In this example, we introduce the method of dynamically adjusting the cooldown time. This method is used to wake up any waiting threads, allowing them to check for the new cooldown time. setCooldownnotify

Using Java's semaphores

Java classes can be used as powerful tools for throttling. The semaphore maintains a set of licenses, where each acquire operation consumes one license and each release operation increments one license. Semaphore

public class SemaphoreRateLimiter {

    private final Semaphore semaphore;

    public SemaphoreRateLimiter(int permits) {
        this.semaphore = new Semaphore(permits);
    }

    public boolean throttle() {
        if (semaphore.tryAcquire()) {
            // Perform the throttled operation
            System.out.println("Throttled operation executed. Permits left: " + semaphore.availablePermits());
            return true;
        } else {
            System.out.println("Request throttled. Try again later.");
            return false;
        }
    }

    public static void main(String[] args) {
        SemaphoreRateLimiter rateLimiter = new SemaphoreRateLimiter(5); // Allow 5 operations concurrently

        for (int i = 0; i < 10; i++) {
            rateLimiter.throttle();
        }
    }
}

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In this example, the class uses a with the specified number of licenses. This method attempts to obtain a license and allows the operation if successful. SemaphoreRateLimiterSemaphorethrottle

Multiple examples in the box

Frameworks such as Spring or Redis provide multiple simple solutions.

Spring AOP for method restrictions

Using Spring's aspect-oriented programming (AOP) capabilities, we can create a method-level restriction mechanism. This approach allows us to intercept method calls and apply throttling logic.

@Aspect
@Component
public class ThrottleAspect {

    private Map<String, Long> lastInvocationMap = new HashMap<>();

    @Pointcut("@annotation(throttle)")
    public void throttledOperation(Throttle throttle) {}

    @Around("throttledOperation(throttle)")
    public Object throttleOperation(ProceedingJoinPoint joinPoint, Throttle throttle) throws Throwable {
        String key = joinPoint.getSignature().toLongString();

        if (!lastInvocationMap.containsKey(key) || System.currentTimeMillis() - lastInvocationMap.get(key) > throttle.value()) {
            lastInvocationMap.put(key, System.currentTimeMillis());
            return joinPoint.proceed();
        } else {
            throw new ThrottleException("Request throttled. Try again later.");
        }
    }
}

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In this example, we have defined a custom annotation and an AOP aspect() to intercept the method using . to check the elapsed time since the last call and allow or block the method accordingly. @ThrottleThrottleAspect@ThrottleThrottleAspect

Using Guava RateLimiter

Google's Guava library provides a class that simplifies the implementation of limits. It allows defining the rate at which operations are allowed. RateLimiter

Let's see how it can be used for method limits: RateLimiter

import com.google.common.util.concurrent.RateLimiter;

@Component
public class ThrottledService {

    private final RateLimiter rateLimiter = RateLimiter.create(5.0); // Allow 5 operations per second

    @Throttle
    public void throttledOperation() {
        if (rateLimiter.tryAcquire()) {
            // Perform the throttled operation
            System.out.println("Throttled operation executed.");
        } else {
            throw new ThrottleException("Request throttled. Try again later.");
        }
    }
}

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In this example, we use Guava to control the execution rate of a method. This method is used to check whether the operation is allowed based on a defined rate. RateLimiterthrottledOperationtryAcquire

Redis as a limiting mechanism

Using an external data store like Redis, we can implement a distributed throttling mechanism. This approach is particularly useful in microservice environments where multiple instances need to coordinate constraints.

@Component
public class RedisThrottleService {

    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    @Value("${throttle.key.prefix}")
    private String keyPrefix;

    @Value("${throttle.max.operations}")
    private int maxOperations;

    @Value("${throttle.duration.seconds}")
    private int durationSeconds;

    public void performThrottledOperation(String userId) {
        String key = keyPrefix + userId;
        Long currentCount = redisTemplate.opsForValue().increment(key);

        if (currentCount != null && currentCount > maxOperations) {
            throw new ThrottleException("Request throttled. Try again later.");
        }

        if (currentCount == 1) {
            // Set expiration for the key
            redisTemplate.expire(key, durationSeconds, TimeUnit.SECONDS);
        }

        // Perform the throttled operation
        System.out.println("Throttled operation executed for user: " + userId);
    }
}

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In this example, we use Redis to store and manage operation counts per user. This method increments the count and checks if the allowed limit has been reached. performThrottledOperation

Conclusion

Throttling plays a key role in maintaining the stability and scalability of an application. In this article, we explore various ways to implement throttling in Java, including simple techniques for using and applying out-of-the-box solutions. Thread.sleep()Semaphore

The choice of restriction strategy depends on factors such as the nature of the application, performance requirements and the level of control required. When implementing restrictions, you must strike a balance between preventing abuse and ensuring a responsive and fair user experience.

When integrating throttling mechanisms into your application, consider monitoring and tuning parameters based on actual usage patterns. When deciding on constraint implementation, some queries may arise, such as how to handle situations where a task exceeds its assigned deadline. In my next article, I plan to explore robust Java implementations that comprehensively address various scenarios.

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