advanced-usage.md

Advanced usage examples

Example of multiple bandwidth

Imagine that you are developing load testing tool, in order to be ensure that testable system is able to dispatch 1000 requests per 1 minute. But you do not want to randomly kill the testable system by generation all 1000 events in one second instead of 1 minute. To solve problem you can construct following bucket:

static final long MAX_WAIT_NANOS = TimeUnit.HOURS.toNanos(1);
// ...

Bucket bucket = Bucket4j.builder()
       // allows 1000 tokens per 1 minute
       .addLimit(Bandwidth.simple(1000, Duration.ofMinutes(1)))
       // but not often then 50 tokens per 1 second
       .addLimit(Bandwidth.simple(50, Duration.ofSeconds(1)))
       .build();

// ...
while (true) {
  // Consume a token from the token bucket.  If a token is not available this method will block until the refill adds one to the bucket.
  if (bucket.tryConsume(1, MAX_WAIT_NANOS, BlockingStrategy.PARKING)) {
       workloadExecutor.execute(new LoadTask());
  };
}

Specifying initial amount of tokens

By default initial size of bucket equals to capacity. But sometimes, you may want to have lesser initial size, for example for case of cold start in order to prevent denial of service:

int initialTokens = 42;
Bandwidth limit = Bandwidth
    .simple(1000, Duration.ofHours(1))
    .withInitialTokens(initialTokens);
Bucket bucket = Bucket4j.builder()
    .addLimit(limit)
    .build();

Turning-off the refill greediness

When bandwidth created via Bandwidth#simple method it does refill in greedy manner, because bandwidth tries to add the tokens to bucket as soon as possible. For example bandwidth with refill "10 tokens per 1 second" will add 1 token per each 100 millisecond, in other words refill will not wait 1 second to regenerate whole bunch of 10 tokens.

If greediness is undesired then you should explicitly choose non-greedy refill. For example the bandwidth bellow will refill 10 tokens per 1 second instead of 1 token per 100 milliseconds:

// When refill created via "intervally" factory method then greediness is turned-off.
Refill refill = Refill.intervally(10, Duration.ofSeconds(1));
Bandwidth bandwidth = Bandwidth.classic(600, refill);

Also it is possible to specify the time when first refill should happen. This option can be used to configure clear interval boundary i.e. start of second, minute, hour, day.

   // imagine that wall clock is 16:20, and we need to schedule the first refill to 17:00
   Instant firstRefillTime = ZonedDateTime.now()
             .truncatedTo(ChronoUnit.HOURS)
             .plus(1, ChronoUnit.HOURS)
             .toInstant();
   
   // see detailed explanation for useAdaptiveInitialTokens in the javadocs for 'intervallyAligned' method 
   boolean useAdaptiveInitialTokens = false;
   
   Bandwidth.classic(400, Refill.intervallyAligned(400, Duration.ofHours(1), firstRefillTime, useAdaptiveInitialTokens));

Returning tokens back to bucket.

The compensating transaction is one of obvious use case when you want to return tokens back to bucket:

Bucket wallet;
...
if (wallet.tryConsume(50)) { // get 50 cents from wallet
    try {
        buyCocaCola();
    } catch(NoCocaColaException e) {
        // return money to wallet
        wallet.addTokens(50);
    } 
}

Customizing time measurement

Choosing nanotime time resolution

By default Bucket4j uses millisecond time resolution, it is preferred time measurement strategy. But rarely(for example benchmarking) you wish the nanosecond precision:

Bucket4j.builder().withNanosecondPrecision()

Be very careful to choose this time measurement strategy, because System.nanoTime() produces inaccurate results, use this strategy only if period of bandwidth is too small that millisecond resolution will be undesired.

Specify custom time measurement strategy

You can specify your custom time meter, if existing miliseconds or nanotime time meters is not enough for your purposes. Imagine that you have a clock, which synchronizes its time with other machines in current cluster, if you want to use time provided by this clock instead of time provided by JVM then you can write something like this:

public class ClusteredTimeMeter implements TimeMeter {

    @Override
    public long currentTimeNanos() {
        return ClusteredClock.currentTimeMillis() * 1_000_000;
    }

}

Bandwidth limit = Bandwidth.simple(100, Duration.ofMinutes(1));
Bucket bucket = Bucket4j.builder()
                .withCustomTimePrecision(new ClusteredTimeMeter())
                .addLimit(limit)
                .build();

Change configuration of bucket on the fly

Sometimes you want to change configuration for already created bucket. For example because client upgrade its service plan and you want to provide additional tokens for him. If you do not want to lose information about already consumed tokens, then you can reconfigure bucket on the fly instead of creation new instance of bucket:

Bucket bucket = ...


Bandwidth newLimit = Bandwidth.simple(newCapacity, Duration.ofMinutes(1));
BucketConfiguration newConfiguration = Bucket4j.configurationBuilder()
                .addLimit(newLimit)
                .build();
bucket.replaceConfiguration(newConfiguration)