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/*
* Copyright 2017-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
*/
package kotlinx.serialization.json
import kotlinx.serialization.json.internal.*
import kotlin.native.ref.*
import kotlin.random.*
/**
* This maps emulate thread-locality of DescriptorSchemaCache for Native.
*
* Custom JSON instances are considered thread-safe (in JVM) and can be frozen and transferred to different workers (in Native).
* Therefore, DescriptorSchemaCache should be either a concurrent freeze-aware map or thread local.
* Each JSON instance have it's own schemaCache, and it's impossible to use @ThreadLocal on non-global vals.
* Thus we make @ThreadLocal this special map: it provides schemaCache for a particular Json instance
* and should be used instead of a member `_schemaCache` on Native.
*
* To avoid memory leaks (when Json instance is no longer in use), WeakReference is used with periodical self-cleaning.
*/
@ThreadLocal
private val jsonToCache: MutableMap<WeakJson, DescriptorSchemaCache> = mutableMapOf()
/**
* Because WeakReference itself does not have proper equals/hashCode
*/
private class WeakJson(json: Json) {
private val ref = WeakReference(json)
private val initialHashCode = json.hashCode()
val isDead: Boolean get() = ref.get() == null
override fun equals(other: Any?): Boolean {
if (other !is WeakJson) return false
val thiz = this.ref.get() ?: return false
val that = other.ref.get() ?: return false
return thiz == that
}
override fun hashCode(): Int = initialHashCode
}
/**
* To maintain O(1) access, we cleanup the table from dead references with 1/size probability
*/
private fun cleanUpWeakMap() {
val size = jsonToCache.size
if (size <= 10) return // 10 is arbitrary small number to ignore polluting
// Roll 1/size probability
if (Random.nextInt(0, size) == 0) {
val iter = jsonToCache.iterator()
while (iter.hasNext()) {
if (iter.next().key.isDead) iter.remove()
}
}
}
/**
* Accessor for DescriptorSchemaCache
*/
internal actual val Json.schemaCache: DescriptorSchemaCache
get() = jsonToCache.getOrPut(WeakJson(this)) { DescriptorSchemaCache() }.also { cleanUpWeakMap() }
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