Package dev.relism.flash.ext.limiter.strategy

Class FixedWindowStrategy

java.lang.Object

dev.relism.flash.ext.limiter.strategy.FixedWindowStrategy

All Implemented Interfaces:

RateLimitStrategy

public final class FixedWindowStrategy
extends Object
implements RateLimitStrategy

Fixed-window rate limit: allows up to LimitConfig.limit() requests per window of LimitConfig.windowMs() milliseconds. The window is aligned to clock time (e.g. 10:00:00 – 10:00:59 for a 60-second window), not sliding.

Implementation

The entire state fits in a single AtomicLong (Bucket.slot0), packed as:

   high 32 bits = reduced epoch  (currentTimeMs / windowMs) invalid input: '&' 0xFFFFFFFFL
   low  32 bits = request count in the current window
 

Each request performs a single CAS loop — no locks, no allocations. At a window boundary the CAS atomically resets the counter to 1.

The reduced epoch wraps every 2^32 × windowMs milliseconds (~13,000 years for a 100 ms window) — collision-free in practice.

Constructor Summary

Constructors

Constructor	Description
FixedWindowStrategy()

Method Summary

Modifier and Type	Method	Description
boolean	check(Bucket bucket, LimitConfig cfg, long[] out)	Checks whether this request is within the limit and updates the bucket atomically.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

FixedWindowStrategy

public FixedWindowStrategy()

Method Details

check

public boolean check(Bucket bucket,
 LimitConfig cfg,
 long[] out)

Description copied from interface: RateLimitStrategy

Checks whether this request is within the limit and updates the bucket atomically.

On return, out contains:

• out[0] — remaining allowed requests in the current window (≥ 0).
• out[1] — Unix epoch seconds at which the quota resets (for X-RateLimit-Reset and Retry-After headers).

Specified by:

check in interface RateLimitStrategy

Parameters:

bucket - per-key state carrier (pre-allocated, never null)

cfg - immutable rule configuration

out - caller-supplied two-element array; values are overwritten on every call

Returns:

true if the request is within the limit and should proceed