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/*
 * Copyright 2016-2021 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license.
 */

package kotlinx.coroutines.internal

import kotlinx.coroutines.*
import java.lang.reflect.*
import java.util.*
import java.util.concurrent.locks.*
import kotlin.concurrent.*

private val throwableFields = Throwable::class.java.fieldsCountOrDefault(-1)
private typealias Ctor = (Throwable) -> Throwable?

private val ctorCache = try {
    if (ANDROID_DETECTED) WeakMapCtorCache
    else ClassValueCtorCache
} catch (e: Throwable) {
    // Fallback on Java 6 or exotic setups
    WeakMapCtorCache
}

@Suppress("UNCHECKED_CAST")
internal fun  tryCopyException(exception: E): E? {
    // Fast path for CopyableThrowable
    if (exception is CopyableThrowable<*>) {
        return runCatching { exception.createCopy() as E? }.getOrNull()
    }
    return ctorCache.get(exception.javaClass).invoke(exception) as E?
}

private fun  createConstructor(clz: Class): Ctor {
    val nullResult: Ctor = { null } // Pre-cache class
    // Skip reflective copy if an exception has additional fields (that are usually populated in user-defined constructors)
    if (throwableFields != clz.fieldsCountOrDefault(0)) return nullResult
    /*
    * Try to reflectively find constructor(), constructor(message, cause), constructor(cause) or constructor(message).
    * Exceptions are shared among coroutines, so we should copy exception before recovering current stacktrace.
    */
    val constructors = clz.constructors.sortedByDescending { it.parameterTypes.size }
    for (constructor in constructors) {
        val result = createSafeConstructor(constructor)
        if (result != null) return result
    }
    return nullResult
}

private fun createSafeConstructor(constructor: Constructor<*>): Ctor? {
    val p = constructor.parameterTypes
    return when (p.size) {
        2 -> when {
            p[0] == String::class.java && p[1] == Throwable::class.java ->
                safeCtor { e -> constructor.newInstance(e.message, e) as Throwable }
            else -> null
        }
        1 -> when (p[0]) {
            Throwable::class.java ->
                safeCtor { e -> constructor.newInstance(e) as Throwable }
            String::class.java ->
                safeCtor { e -> (constructor.newInstance(e.message) as Throwable).also { it.initCause(e) } }
            else -> null
        }
        0 -> safeCtor { e -> (constructor.newInstance() as Throwable).also { it.initCause(e) } }
        else -> null
    }
}

private inline fun safeCtor(crossinline block: (Throwable) -> Throwable): Ctor =
    { e -> runCatching { block(e) }.getOrNull() }

private fun Class<*>.fieldsCountOrDefault(defaultValue: Int) =
    kotlin.runCatching { fieldsCount() }.getOrDefault(defaultValue)

private tailrec fun Class<*>.fieldsCount(accumulator: Int = 0): Int {
    val fieldsCount = declaredFields.count { !Modifier.isStatic(it.modifiers) }
    val totalFields = accumulator + fieldsCount
    val superClass = superclass ?: return totalFields
    return superClass.fieldsCount(totalFields)
}

internal abstract class CtorCache {
    abstract fun get(key: Class): Ctor
}

private object WeakMapCtorCache : CtorCache() {
    private val cacheLock = ReentrantReadWriteLock()
    private val exceptionCtors: WeakHashMap, Ctor> = WeakHashMap()

    override fun get(key: Class): Ctor {
        cacheLock.read { exceptionCtors[key]?.let { return it } }
        cacheLock.write {
            exceptionCtors[key]?.let { return it }
            return createConstructor(key).also { exceptionCtors[key] = it }
        }
    }
}

@IgnoreJreRequirement
private object ClassValueCtorCache : CtorCache() {
    private val cache = object : ClassValue() {
        override fun computeValue(type: Class<*>?): Ctor {
            @Suppress("UNCHECKED_CAST")
            return createConstructor(type as Class)
        }
    }

    override fun get(key: Class): Ctor = cache.get(key)
}




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