awaitFirst

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## 0.4.18
 
+* `Coroutines`:
+    * New extension `Iterable<Deferred>#awaitFirst` has been added
 * `Serialization`
     * `Base 64`
         * New `Base64ByteArraySerializer` has been added

coroutines/src/commonMain/kotlin/dev/inmo/micro_utils/coroutines/AwaitFirst.kt

@@ -0,0 +1,32 @@
+package dev.inmo.micro_utils.coroutines
+
+import kotlinx.coroutines.*
+import kotlin.coroutines.*
+
+suspend fun <T> Iterable<Deferred<T>>.awaitFirst(
+    scope: CoroutineScope,
+    cancelOnResult: Boolean = true
+): T = suspendCoroutine<T> { continuation ->
+    scope.launch(SupervisorJob()) {
+        val scope = this
+        forEach {
+            scope.launch {
+                continuation.resume(it.await())
+                scope.cancel()
+            }
+        }
+    }
+}.also {
+    if (cancelOnResult) {
+        forEach {
+            try {
+                it.cancel()
+            } catch (e: IllegalStateException) {
+                e.printStackTrace()
+            }
+        }
+    }
+}
+suspend fun <T> Iterable<Deferred<T>>.awaitFirst(
+    cancelOthers: Boolean = true
+): T = awaitFirst(CoroutineScope(coroutineContext), cancelOthers)

coroutines/src/jvmTest/kotlin/dev/inmo/micro_utils/coroutines/AwaitFirstTests.kt

@@ -0,0 +1,34 @@
+package dev.inmo.micro_utils.coroutines
+
+import kotlinx.coroutines.*
+import org.junit.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertTrue
+
+class AwaitFirstTests {
+    private fun CoroutineScope.createTestDeferred(value: Int, wait: Long = 100000) = async(start = CoroutineStart.LAZY) { delay(wait); value }
+    @Test
+    fun testThatAwaitFirstIsWorkingCorrectly() {
+        val baseScope = CoroutineScope(Dispatchers.Default)
+        val resultDeferred = baseScope.createTestDeferred(-1, 0)
+        val deferreds = listOf(
+            baseScope.async { createTestDeferred(0) },
+            baseScope.async { createTestDeferred(1) },
+            baseScope.async { createTestDeferred(2) },
+            resultDeferred
+        )
+        val controlJob = baseScope.launch {
+            delay(1000000)
+        }
+        val result = baseScope.launchSynchronously {
+            val result = deferreds.awaitFirst(baseScope)
+
+            assertTrue(baseScope.isActive)
+            assertTrue(controlJob.isActive)
+
+            result
+        }
+        assertEquals(baseScope.launchSynchronously { resultDeferred.await() }, result)
+        assertTrue(deferreds.all { it == resultDeferred || it.isCancelled })
+    }
+}