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ntfy/util/limit.go

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2021-11-01 21:39:40 +01:00
package util
import (
"errors"
"sync"
)
// ErrLimitReached is the error returned by the Limiter and LimitWriter when the predefined limit has been reached
var ErrLimitReached = errors.New("limit reached")
// Limiter is a helper that allows adding values up to a well-defined limit. Once the limit is reached
// ErrLimitReached will be returned. Limiter may be used by multiple goroutines.
type Limiter struct {
value int64
limit int64
mu sync.Mutex
}
// NewLimiter creates a new Limiter
func NewLimiter(limit int64) *Limiter {
return &Limiter{
limit: limit,
}
}
// Add adds n to the limiters internal value, but only if the limit has not been reached. If the limit would be
// exceeded after adding n, ErrLimitReached is returned.
func (l *Limiter) Add(n int64) error {
l.mu.Lock()
defer l.mu.Unlock()
if l.limit == 0 {
l.value += n
return nil
} else if l.value+n <= l.limit {
l.value += n
return nil
} else {
return ErrLimitReached
}
}
// Sub subtracts a value from the limiters internal value
func (l *Limiter) Sub(n int64) {
l.Add(-n)
}
// Set sets the value of the limiter to n. This function ignores the limit. It is meant to set the value
// based on reality.
func (l *Limiter) Set(n int64) {
l.mu.Lock()
l.value = n
l.mu.Unlock()
}
// Value returns the internal value of the limiter
func (l *Limiter) Value() int64 {
l.mu.Lock()
defer l.mu.Unlock()
return l.value
}
// Limit returns the defined limit
func (l *Limiter) Limit() int64 {
return l.limit
}