From 91c87a931328ab5f2457e5bb8f09774694b1364d Mon Sep 17 00:00:00 2001
From: Steve Elliott <steell@google.com>
Date: Sat, 3 Sep 2022 22:08:28 -0400
Subject: [PATCH] Add race() utility function

Bug: 241121499
Test: atest RaceSuspendTest
Change-Id: I4f76a335f7c87f4273d631ab095bfe4f9fe5a1dd
---
 .../android/systemui/util/kotlin/Suspend.kt   | 35 ++++++++++++
 .../systemui/util/kotlin/SuspendUtilTests.kt  | 55 +++++++++++++++++++
 2 files changed, 90 insertions(+)
 create mode 100644 packages/SystemUI/src/com/android/systemui/util/kotlin/Suspend.kt
 create mode 100644 packages/SystemUI/tests/src/com/android/systemui/util/kotlin/SuspendUtilTests.kt

diff --git a/packages/SystemUI/src/com/android/systemui/util/kotlin/Suspend.kt b/packages/SystemUI/src/com/android/systemui/util/kotlin/Suspend.kt
new file mode 100644
index 0000000000000..2e551f1e1beec
--- /dev/null
+++ b/packages/SystemUI/src/com/android/systemui/util/kotlin/Suspend.kt
@@ -0,0 +1,35 @@
+/*
+ * 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() }
+}
diff --git a/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/SuspendUtilTests.kt b/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/SuspendUtilTests.kt
new file mode 100644
index 0000000000000..6848b836a3489
--- /dev/null
+++ b/packages/SystemUI/tests/src/com/android/systemui/util/kotlin/SuspendUtilTests.kt
@@ -0,0 +1,55 @@
+/*
+ * 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)
+    }
+}