Package com.google.common.util.concurrent

Class RateLimiter

  • @Beta
@GwtIncompatible
public abstract class RateLimiter
extends Object
    A rate limiter. Conceptually, a rate limiter distributes permits at a configurable rate. Each acquire() blocks if necessary until a permit is available, and then takes it. Once acquired, permits need not be released.

    RateLimiter is safe for concurrent use: It will restrict the total rate of calls from all threads. Note, however, that it does not guarantee fairness.

    Rate limiters are often used to restrict the rate at which some physical or logical resource is accessed. This is in contrast to Semaphore which restricts the number of concurrent accesses instead of the rate (note though that concurrency and rate are closely related, e.g. see Little's Law).

    A RateLimiter is defined primarily by the rate at which permits are issued. Absent additional configuration, permits will be distributed at a fixed rate, defined in terms of permits per second. Permits will be distributed smoothly, with the delay between individual permits being adjusted to ensure that the configured rate is maintained.

    It is possible to configure a RateLimiter to have a warmup period during which time the permits issued each second steadily increases until it hits the stable rate.

    As an example, imagine that we have a list of tasks to execute, but we don't want to submit more than 2 per second: 

    
 final RateLimiter rateLimiter = RateLimiter.create(2.0); // rate is "2 permits per second"
 void submitTasks(List<Runnable> tasks, Executor executor) {
   for (Runnable task : tasks) {
     rateLimiter.acquire(); // may wait
     executor.execute(task);
   }
 }

    As another example, imagine that we produce a stream of data, and we want to cap it at 5kb per second. This could be accomplished by requiring a permit per byte, and specifying a rate of 5000 permits per second: 

    
 final RateLimiter rateLimiter = RateLimiter.create(5000.0); // rate = 5000 permits per second
 void submitPacket(byte[] packet) {
   rateLimiter.acquire(packet.length);
   networkService.send(packet);
 }

    It is important to note that the number of permits requested never affects the throttling of the request itself (an invocation to acquire(1) and an invocation to acquire(1000) will result in exactly the same throttling, if any), but it affects the throttling of the next request. I.e., if an expensive task arrives at an idle RateLimiter, it will be granted immediately, but it is the next request that will experience extra throttling, thus paying for the cost of the expensive task.

    Since:
    13.0
    Author:
    Dimitris Andreou

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      double acquire()
      Acquires a single permit from this RateLimiter, blocking until the request can be granted.
      double acquire​(int permits)
      Acquires the given number of permits from this RateLimiter, blocking until the request can be granted.
      static RateLimiter create​(double permitsPerSecond)
      Creates a RateLimiter with the specified stable throughput, given as "permits per second" (commonly referred to as QPS, queries per second).
      static RateLimiter create​(double permitsPerSecond, long warmupPeriod, TimeUnit unit)
      Creates a RateLimiter with the specified stable throughput, given as "permits per second" (commonly referred to as QPS, queries per second), and a warmup period, during which the RateLimiter smoothly ramps up its rate, until it reaches its maximum rate at the end of the period (as long as there are enough requests to saturate it).
      double getRate()
      Returns the stable rate (as permits per seconds) with which this RateLimiter is configured with.
      void setRate​(double permitsPerSecond)
      Updates the stable rate of this RateLimiter, that is, the permitsPerSecond argument provided in the factory method that constructed the RateLimiter.
      String toString()
      Returns a string representation of the object.
      boolean tryAcquire()
      Acquires a permit from this RateLimiter if it can be acquired immediately without delay.
      boolean tryAcquire​(int permits)
      Acquires permits from this RateLimiter if it can be acquired immediately without delay.
      boolean tryAcquire​(int permits, long timeout, TimeUnit unit)
      Acquires the given number of permits from this RateLimiter if it can be obtained without exceeding the specified timeout, or returns false immediately (without waiting) if the permits would not have been granted before the timeout expired.
      boolean tryAcquire​(long timeout, TimeUnit unit)
      Acquires a permit from this RateLimiter if it can be obtained without exceeding the specified timeout, or returns false immediately (without waiting) if the permit would not have been granted before the timeout expired.

    • Method Detail

      • create

        public static RateLimiter create​(double permitsPerSecond)
        Creates a RateLimiter with the specified stable throughput, given as "permits per second" (commonly referred to as QPS, queries per second).

        The returned RateLimiter ensures that on average no more than permitsPerSecond are issued during any given second, with sustained requests being smoothly spread over each second. When the incoming request rate exceeds permitsPerSecond the rate limiter will release one permit every (1.0 / permitsPerSecond) seconds. When the rate limiter is unused, bursts of up to permitsPerSecond permits will be allowed, with subsequent requests being smoothly limited at the stable rate of permitsPerSecond.

        Parameters:
        permitsPerSecond - the rate of the returned RateLimiter, measured in how many permits become available per second
        Throws:
        IllegalArgumentException - if permitsPerSecond is negative or zero

      • create

        public static RateLimiter create​(double permitsPerSecond,
                                 long warmupPeriod,
                                 TimeUnit unit)
        Creates a RateLimiter with the specified stable throughput, given as "permits per second" (commonly referred to as QPS, queries per second), and a warmup period, during which the RateLimiter smoothly ramps up its rate, until it reaches its maximum rate at the end of the period (as long as there are enough requests to saturate it). Similarly, if the RateLimiter is left unused for a duration of warmupPeriod, it will gradually return to its "cold" state, i.e. it will go through the same warming up process as when it was first created.

        The returned RateLimiter is intended for cases where the resource that actually fulfills the requests (e.g., a remote server) needs "warmup" time, rather than being immediately accessed at the stable (maximum) rate.

        The returned RateLimiter starts in a "cold" state (i.e. the warmup period will follow), and if it is left unused for long enough, it will return to that state.

        Parameters:
        permitsPerSecond - the rate of the returned RateLimiter, measured in how many permits become available per second
        warmupPeriod - the duration of the period where the RateLimiter ramps up its rate, before reaching its stable (maximum) rate
        unit - the time unit of the warmupPeriod argument
        Throws:
        IllegalArgumentException - if permitsPerSecond is negative or zero or warmupPeriod is negative

      • setRate

        public final void setRate​(double permitsPerSecond)
        Updates the stable rate of this RateLimiter, that is, the permitsPerSecond argument provided in the factory method that constructed the RateLimiter. Currently throttled threads will not be awakened as a result of this invocation, thus they do not observe the new rate; only subsequent requests will.

        Note though that, since each request repays (by waiting, if necessary) the cost of the previous request, this means that the very next request after an invocation to setRate will not be affected by the new rate; it will pay the cost of the previous request, which is in terms of the previous rate.

        The behavior of the RateLimiter is not modified in any other way, e.g. if the RateLimiter was configured with a warmup period of 20 seconds, it still has a warmup period of 20 seconds after this method invocation.

        Parameters:
        permitsPerSecond - the new stable rate of this RateLimiter
        Throws:
        IllegalArgumentException - if permitsPerSecond is negative or zero

      • getRate

        public final double getRate()
        Returns the stable rate (as permits per seconds) with which this RateLimiter is configured with. The initial value of this is the same as the permitsPerSecond argument passed in the factory method that produced this RateLimiter, and it is only updated after invocations to setRate(double).

      • acquire

        @CanIgnoreReturnValue
public double acquire()
        Acquires a single permit from this RateLimiter, blocking until the request can be granted. Tells the amount of time slept, if any.

        This method is equivalent to acquire(1).

        Returns:
        time spent sleeping to enforce rate, in seconds; 0.0 if not rate-limited
        Since:
        16.0 (present in 13.0 with void return type})

      • acquire

        @CanIgnoreReturnValue
public double acquire​(int permits)
        Acquires the given number of permits from this RateLimiter, blocking until the request can be granted. Tells the amount of time slept, if any.
        Parameters:
        permits - the number of permits to acquire
        Returns:
        time spent sleeping to enforce rate, in seconds; 0.0 if not rate-limited
        Throws:
        IllegalArgumentException - if the requested number of permits is negative or zero
        Since:
        16.0 (present in 13.0 with void return type})

      • tryAcquire

        public boolean tryAcquire​(long timeout,
                          TimeUnit unit)
        Acquires a permit from this RateLimiter if it can be obtained without exceeding the specified timeout, or returns false immediately (without waiting) if the permit would not have been granted before the timeout expired.

        This method is equivalent to tryAcquire(1, timeout, unit).

        Parameters:
        timeout - the maximum time to wait for the permit. Negative values are treated as zero.
        unit - the time unit of the timeout argument
        Returns:
        true if the permit was acquired, false otherwise
        Throws:
        IllegalArgumentException - if the requested number of permits is negative or zero

      • tryAcquire

        public boolean tryAcquire​(int permits)
        Acquires permits from this RateLimiter if it can be acquired immediately without delay.

        This method is equivalent to tryAcquire(permits, 0, anyUnit).

        Parameters:
        permits - the number of permits to acquire
        Returns:
        true if the permits were acquired, false otherwise
        Throws:
        IllegalArgumentException - if the requested number of permits is negative or zero
        Since:
        14.0

      • tryAcquire

        public boolean tryAcquire()
        Acquires a permit from this RateLimiter if it can be acquired immediately without delay.

        This method is equivalent to tryAcquire(1).

        Returns:
        true if the permit was acquired, false otherwise
        Since:
        14.0

      • tryAcquire

        public boolean tryAcquire​(int permits,
                          long timeout,
                          TimeUnit unit)
        Acquires the given number of permits from this RateLimiter if it can be obtained without exceeding the specified timeout, or returns false immediately (without waiting) if the permits would not have been granted before the timeout expired.
        Parameters:
        permits - the number of permits to acquire
        timeout - the maximum time to wait for the permits. Negative values are treated as zero.
        unit - the time unit of the timeout argument
        Returns:
        true if the permits were acquired, false otherwise
        Throws:
        IllegalArgumentException - if the requested number of permits is negative or zero

      • toString

        public String toString()
        Description copied from class: java.lang.Object
        Returns a string representation of the object. In general, the toString method returns a string that "textually represents" this object. The result should be a concise but informative representation that is easy for a person to read. It is recommended that all subclasses override this method.

        The toString method for class Object returns a string consisting of the name of the class of which the object is an instance, the at-sign character `@', and the unsigned hexadecimal representation of the hash code of the object. In other words, this method returns a string equal to the value of: 

         getClass().getName() + '@' + Integer.toHexString(hashCode())
        Overrides:
        toString in class Object
        Returns:
        a string representation of the object.