Add race() utility function

/*

 * Copyright (C) 2022 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.android.systemui.util.kotlin

import kotlinx.coroutines.CompletableDeferred

import kotlinx.coroutines.coroutineScope

import kotlinx.coroutines.launch

/**

 * Runs the given [blocks] in parallel, returning the result of the first one to complete, and

 * cancelling all others.

 */

suspend fun <R> race(vararg blocks: suspend () -> R): R = coroutineScope {

    val completion = CompletableDeferred<R>()

    val raceJob = launch {

        for (block in blocks) {

            launch { completion.complete(block()) }

        }

    }

    completion.await().also { raceJob.cancel() }

}

/*

 * Copyright (C) 2022 The Android Open Source Project

 *

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.android.systemui.util.kotlin

import android.testing.AndroidTestingRunner

import androidx.test.filters.SmallTest

import com.android.systemui.SysuiTestCase

import com.google.common.truth.Truth.assertThat

import kotlinx.coroutines.CompletableDeferred

import kotlinx.coroutines.async

import kotlinx.coroutines.awaitCancellation

import kotlinx.coroutines.runBlocking

import org.junit.Test

import org.junit.runner.RunWith

@SmallTest

@RunWith(AndroidTestingRunner::class)

class RaceSuspendTest : SysuiTestCase() {

    @Test

    fun raceSimple() = runBlocking {

        val winner = CompletableDeferred<Int>()

        val result = async {

            race(

                { winner.await() },

                { awaitCancellation() },

            )

        }

        winner.complete(1)

        assertThat(result.await()).isEqualTo(1)

    }

    @Test

    fun raceImmediate() = runBlocking {

        assertThat(

            race<Int>(

                { 1 },

                { 2 },

            )

        ).isEqualTo(1)

    }

}