commonMain.ComputeOnNullMutableProperty.kt Maven / Gradle / Ivy
/*
* Copyright 2019-2021 Mamoe Technologies and contributors.
*
* 此源代码的使用受 GNU AFFERO GENERAL PUBLIC LICENSE version 3 许可证的约束, 可以在以下链接找到该许可证.
* Use of this source code is governed by the GNU AGPLv3 license that can be found through the following link.
*
* https://github.com/mamoe/mirai/blob/master/LICENSE
*/
package net.mamoe.mirai.utils
import kotlinx.atomicfu.atomic
import kotlin.reflect.KProperty
public fun computeOnNullMutableProperty(initializer: () -> T): ComputeOnNullMutableProperty =
ComputeOnNullMutablePropertyImpl(initializer)
public interface ComputeOnNullMutableProperty {
public fun get(): V
public fun set(value: V?)
public operator fun getValue(thisRef: Any?, property: KProperty<*>): V = get()
public operator fun setValue(thisRef: Any?, property: KProperty<*>, value: V?): Unit = set(value)
}
private class ComputeOnNullMutablePropertyImpl(
private val initializer: () -> T
) : ComputeOnNullMutableProperty {
private val value = atomic(null)
override tailrec fun get(): T {
return when (val v = this.value.value) {
null -> synchronized(this) {
if (this.value.value === null) {
val value = this.initializer()
// compiler inserts
this.value.compareAndSet(null, value) // setValue prevails
return get()
} else this.value.value as T
}
else -> v
}
}
override fun set(value: T?) {
this.value.value = value
}
}
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