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Kotlin Standard Library

There is a newer version: 2.1.0-RC

/*
 * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
 * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
 */

@file:JvmName("LocksKt")
package kotlin.concurrent

import java.util.concurrent.locks.Lock
import java.util.concurrent.locks.ReentrantReadWriteLock
import kotlin.contracts.*

/**
 * Executes the given [action] under this lock.
 * @return the return value of the action.
 */
@kotlin.internal.InlineOnly
public inline fun  Lock.withLock(action: () -> T): T {
    contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
    lock()
    try {
        return action()
    } finally {
        unlock()
    }
}

/**
 * Executes the given [action] under the read lock of this lock.
 * @return the return value of the action.
 */
@kotlin.internal.InlineOnly
public inline fun  ReentrantReadWriteLock.read(action: () -> T): T {
    contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
    val rl = readLock()
    rl.lock()
    try {
        return action()
    } finally {
        rl.unlock()
    }
}

/**
 * Executes the given [action] under the write lock of this lock.
 *
 * The function does upgrade from read to write lock if needed, but this upgrade is not atomic
 * as such upgrade is not supported by [ReentrantReadWriteLock].
 * In order to do such upgrade this function first releases all read locks held by this thread,
 * then acquires write lock, and after releasing it acquires read locks back again.
 *
 * Therefore if the [action] inside write lock has been initiated by checking some condition,
 * the condition must be rechecked inside the [action] to avoid possible races.
 *
 * @return the return value of the action.
 */
@kotlin.internal.InlineOnly
public inline fun  ReentrantReadWriteLock.write(action: () -> T): T {
    contract { callsInPlace(action, InvocationKind.EXACTLY_ONCE) }
    val rl = readLock()

    val readCount = if (writeHoldCount == 0) readHoldCount else 0
    repeat(readCount) { rl.unlock() }

    val wl = writeLock()
    wl.lock()
    try {
        return action()
    } finally {
        repeat(readCount) { rl.lock() }
        wl.unlock()
    }
}