RateLimiter

A deterministic testable rate limiter that uses two variables:

• Permits per second. This is the application's configured rate. We express as a per-second rate but use it as a time-between-permits. For example, 250 permits per second is a permit every 4 milliseconds. This may be zero, in which case all acquire attempts will return false.

• Window size. If the application specified 250 permits per second, that doesn't specify how many permits can be returned at once. An implementation could strictly return 1 permit every 4 milliseconds, or batches of 1000 permits every 4 seconds. This class hard codes the window size to 1 second. Small windows shrink batch sizes which is inefficient; large windows grow batch sizes which is bursty. This class uses 1 second to balance latency and throughput.

The implementation tracks a future timestamp that permits are consumed until.

This class is similar to Guava's rate limiter. Unlike Guava's rate limiter this class is testable by application code using the rate limiter. It also has very predictable behavior because its internal mechanisms are simpler than Guava's.