synchronize property getters/setters

user_2223059 0
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So I'm trying to get a handle on how Kotlin handles synchronization of properties. If I have this class:

class Foo {
    var a = 0
    var b = 0
}

and I want to make sure that a & b have all access synchronized. How would I do it? I've tried using the annotation:

class Foo {
    @Synchronized
    var a = 0
    @Synchronized
    var b = 0
}

but Kotlin gives me a compiler error:

This annotation is not applicable to target 'member property with backing field'

I'm just trying to get a better handle on thread safety in Kotlin. It's something that I've always been OCD about in Java, and I'm trying to figure out how to properly handle it in Kotlin.

kotlin java
2 Answers

Followed by the @Kirill Rakhman's answer, use of Delegates could be more performant if there is tons of contention to the same object since it locks on the delegate rather than the whole object.

class Foo {
    var a by Synchronize(0)
    var b by Synchronize(0)
}

class Synchronize<T>(defaultValue: T): ReadWriteProperty<Any, T> {
    private var backingField = defaultValue

    override fun getValue(thisRef: Any, property: KProperty<*>): T {
        return synchronized(this) {
            backingField
        }
    }

    override fun setValue(thisRef: Any, property: KProperty<*>, value: T) {
        synchronized(this) {
            backingField = value
        }
    }
}

References: Kotlin Delegated Properties Reddit Discussion

user_52650790
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