github.com/weaviate/weaviate@v1.24.6/usecases/ratelimiter/limiter.go (about)

     1  //                           _       _
     2  // __      _____  __ ___   ___  __ _| |_ ___
     3  // \ \ /\ / / _ \/ _` \ \ / / |/ _` | __/ _ \
     4  //  \ V  V /  __/ (_| |\ V /| | (_| | ||  __/
     5  //   \_/\_/ \___|\__,_| \_/ |_|\__,_|\__\___|
     6  //
     7  //  Copyright © 2016 - 2024 Weaviate B.V. All rights reserved.
     8  //
     9  //  CONTACT: hello@weaviate.io
    10  //
    11  
    12  package ratelimiter
    13  
    14  import "sync/atomic"
    15  
    16  // Limiter is a thread-safe counter that can be used for rate-limiting requests
    17  type Limiter struct {
    18  	max     int64
    19  	current int64
    20  }
    21  
    22  // New creates a [Limiter] with the specified maximum concurrent requests
    23  func New(maxRequests int) *Limiter {
    24  	return &Limiter{
    25  		max: int64(maxRequests),
    26  	}
    27  }
    28  
    29  // If there is still room, TryInc, increases the counter and returns true. If
    30  // there are too many concurrent requests it does not increase the counter and
    31  // returns false
    32  func (l *Limiter) TryInc() bool {
    33  	if l.max <= 0 {
    34  		return true
    35  	}
    36  
    37  	new := atomic.AddInt64(&l.current, 1)
    38  
    39  	if new <= l.max {
    40  		return true
    41  	}
    42  
    43  	// undo unsuccessful increment
    44  	atomic.AddInt64(&l.current, -1)
    45  	return false
    46  }
    47  
    48  func (l *Limiter) Dec() {
    49  	if l.max <= 0 {
    50  		return
    51  	}
    52  
    53  	new := atomic.AddInt64(&l.current, -1)
    54  	if new < 0 {
    55  		// Should not happen unless some client called Dec multiple times.
    56  		// Try to reset current to 0. It's ok if swap doesn't happen, since
    57  		// someone else must've succeeded at fixing current value.
    58  		atomic.CompareAndSwapInt64(&l.current, new, 0)
    59  	}
    60  }