78 lines
1.7 KiB
Go
78 lines
1.7 KiB
Go
package lazy
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import (
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"sync"
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"time"
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)
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// Lazy is an object that a lazily-initialized value of type T.
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//
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// A Lazy must not be copied after first use.
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type Lazy[T any] struct {
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once sync.Once
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value T
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m sync.RWMutex // m protects resetting this lazy
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lastReset time.Time // last time this mutex was reset
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}
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// Get returns the value associated with this Lazy.
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//
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// If no other call to Get has started or completed an initialization, initializes the value using the init function.
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// Otherwise, it returns the initialized value.
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//
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// If init panics, the initization is considered to be completed.
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// Future calls to Get() do not invoke init, and the zero value of T is returned.
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//
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// Get may safely be called concurrently.
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func (lazy *Lazy[T]) Get(init func() T) T {
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lazy.m.RLock()
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defer lazy.m.RUnlock()
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lazy.once.Do(func() {
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lazy.value = init()
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})
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return lazy.value
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}
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// Reset resets this Lazy, deleting any previously associated value.
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//
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// May be called concurrently with [Get].
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// Future calls to [Get] will invoke init.
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func (lazy *Lazy[T]) Reset() {
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lazy.m.Lock()
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defer lazy.m.Unlock()
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lazy.reset()
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}
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// ResetAfter resets this lazy if more than d time has passed since the last reset.
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// If ResetAfter cannot lock, then it does not reset.
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//
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// May be called concurrently with other functions on this lazy.
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func (lazy *Lazy[T]) ResetAfter(d time.Duration) {
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if !lazy.m.TryLock() {
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return
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}
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defer lazy.m.Unlock()
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if time.Since(lazy.lastReset) < d {
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return
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}
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lazy.reset()
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}
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// reset implements resetting this lazy.
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// m myst be held for writing.
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func (lazy *Lazy[T]) reset() {
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// reset the once
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lazy.once = sync.Once{}
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// reset the value
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var t T
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lazy.value = t
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// time of the last reset
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lazy.lastReset = time.Now()
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}
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