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ferret/pkg/drivers/common/lazy.go

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package common
import (
"context"
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"sync"
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"github.com/MontFerret/ferret/pkg/runtime/core"
"github.com/MontFerret/ferret/pkg/runtime/values"
)
type (
LazyValueFactory func(ctx context.Context) (core.Value, error)
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LazyValue struct {
sync.Mutex
factory LazyValueFactory
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ready bool
value core.Value
err error
}
)
func NewLazyValue(factory LazyValueFactory) *LazyValue {
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lz := new(LazyValue)
lz.ready = false
lz.factory = factory
lz.value = values.None
return lz
}
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// Ready indicates whether the value is ready.
// @returns (Boolean) - Boolean value indicating whether the value is ready.
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func (lv *LazyValue) Ready() bool {
lv.Lock()
defer lv.Unlock()
return lv.ready
}
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// Read returns an underlying value.
// Not thread safe. Should not mutated.
// @returns (Value) - Underlying value if successfully loaded, otherwise error
func (lv *LazyValue) Read(ctx context.Context) (core.Value, error) {
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lv.Lock()
defer lv.Unlock()
if !lv.ready {
lv.load(ctx)
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}
return lv.value, lv.err
}
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// Write safely mutates an underlying value.
// Loads a value if it's not ready.
// Thread safe.
func (lv *LazyValue) Write(ctx context.Context, writer func(v core.Value, err error)) {
lv.Lock()
defer lv.Unlock()
if !lv.ready {
lv.load(ctx)
}
writer(lv.value, lv.err)
}
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// Reset resets the storage.
// Next call of Read will trigger the factory function again.
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func (lv *LazyValue) Reset() {
lv.Lock()
defer lv.Unlock()
lv.ready = false
lv.value = values.None
lv.err = nil
}
func (lv *LazyValue) load(ctx context.Context) {
val, err := lv.factory(ctx)
if err == nil {
lv.value = val
lv.err = nil
} else {
lv.value = values.None
lv.err = err
}
lv.ready = true
}