Add concatArrayEager operator

README.md

@@ -28,6 +28,7 @@ Table of contents
 - Sources
   - `range`
   - `timer`
+  - [`concatArrayEager`](#concatarrayeager)
 - Intermediate Flow operators (`FlowExtensions`)
   - `Flow.concatWith`
   - `Flow.groupBy`
@@ -259,4 +260,24 @@ uws.take(5).collect { println(it) }
 
 // prints lines 11..15
 uws.take(5).collect { println(it) }
+```
+
+## concatArrayEager
+
+Launches all at once and emits all items from a source before items of the next are emitted.
+
+For example, given two sources, if the first is slow, the items of the second won't be emitted until the first has
+finished emitting its items. This operators allows all sources to generate items in parallel but then still emit those
+items in the order their respective `Flow`s are listed.
+
+Note that each source is consumed in an unbounded manner and thus, depending on the speed of
+the current source and the collector, the operator may retain items longer and may use more memory
+during its execution.
+
+```kotlin
+concatArrayEager(
+        range(1, 5).onStart { delay(200) },
+        range(6, 5)
+)
+.assertResult(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
 ```

gradle.properties

@@ -1,5 +1,5 @@
 GROUP=com.github.akarnokd
-VERSION_NAME=0.0.8
+VERSION_NAME=0.0.9
 
 POM_ARTIFACT_ID=kotlin-flow-extensions
 POM_NAME=Kotlin Flow Extensions

src/main/kotlin/hu/akarnokd/kotlin/flow/FlowExtensions.kt

@@ -196,7 +196,7 @@ fun <T> Flow<T>.toList() : Flow<List<T>> {
  * Drops items from the upstream when the downstream is not ready to receive them.
  */
 @FlowPreview
-fun <T> Flow<T>.onBackpressurureDrop() : Flow<T> = FlowOnBackpressureDrop(this)
+fun <T> Flow<T>.onBackpressureDrop() : Flow<T> = FlowOnBackpressureDrop(this)
 
 /**
  * Maps items from the upstream to [Flow] and relays its items while dropping upstream items
@@ -211,12 +211,21 @@ fun <T, R> Flow<T>.flatMapDrop(mapper: suspend (T) -> Flow<R>) : Flow<R> = FlowF
 @FlowPreview
 fun <T> mergeArray(vararg sources: Flow<T>) : Flow<T> = FlowMergeArray(sources)
 
+/**
+ * Launches all [sources] at once and emits all items from a source before items of the next are emitted.
+ * Note that each source is consumed in an unbounded manner and thus, depending on the speed of
+ * the current source and the collector, the operator may retain items longer and may use more memory
+ * during its execution.
+ */
+@FlowPreview
+fun <T> concatArrayEager(vararg sources: Flow<T>) : Flow<T> = FlowConcatArrayEager(sources)
+
 // -----------------------------------------------------------------------------------------
 // Parallel Extensions
 // -----------------------------------------------------------------------------------------
 
 /**
- * Consumes the upstream and dispatches individual items to a parrallel rail
+ * Consumes the upstream and dispatches individual items to a parallel rail
  * of the parallel flow for further consumption.
  */
 fun <T> Flow<T>.parallel(parallelism: Int, runOn: (Int) -> CoroutineDispatcher) : ParallelFlow<T> =

src/main/kotlin/hu/akarnokd/kotlin/flow/impl/FlowConcatArrayEager.kt

@@ -0,0 +1,78 @@
+/*
+ * Copyright 2019-2020 David Karnok
+ *
+ * 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 hu.akarnokd.kotlin.flow.impl
+
+import hu.akarnokd.kotlin.flow.Resumable
+import kotlinx.coroutines.*
+import kotlinx.coroutines.flow.AbstractFlow
+import kotlinx.coroutines.flow.Flow
+import kotlinx.coroutines.flow.FlowCollector
+import java.util.concurrent.ConcurrentLinkedQueue
+import java.util.concurrent.atomic.AtomicInteger
+import kotlinx.coroutines.flow.collect
+import java.util.concurrent.atomic.AtomicIntegerArray
+
+@FlowPreview
+class FlowConcatArrayEager<T>(private val sources: Array<out Flow<T>>) : AbstractFlow<T>() {
+
+    @InternalCoroutinesApi
+    override suspend fun collectSafely(collector: FlowCollector<T>) {
+        val n = sources.size
+        val queues = Array(n) { ConcurrentLinkedQueue<T>() }
+        val done = AtomicIntegerArray(n)
+        var index = 0;
+        val reader = Resumable()
+
+        coroutineScope {
+            for (i in 0 until n) {
+                val f = sources[i]
+                val q = queues[i]
+                val j = i
+                launch {
+                    try {
+                        f.collect {
+                            q.offer(it)
+                            reader.resume()
+                        }
+                    } finally {
+                        done.set(j, 1)
+                        reader.resume()
+                    }
+                }
+            }
+
+
+            while (isActive && index < n) {
+                val q = queues[index]
+                val d = done.get(index) != 0
+
+                if (d && q.isEmpty()) {
+                    index++
+                    continue
+                }
+
+                val v = q.poll()
+                if (v != null) {
+                    collector.emit(v)
+                    continue;
+                }
+
+                reader.await()
+            }
+        }
+    }
+}

src/test/kotlin/hu/akarnokd/kotlin/flow/impl/FlowConcatArrayEagerTest.kt

@@ -0,0 +1,54 @@
+package hu.akarnokd.kotlin.flow.impl
+
+import hu.akarnokd.kotlin.flow.assertResult
+import hu.akarnokd.kotlin.flow.concatArrayEager
+import hu.akarnokd.kotlin.flow.range
+import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.delay
+import kotlinx.coroutines.flow.onEach
+import kotlinx.coroutines.flow.onStart
+import kotlinx.coroutines.flow.take
+import kotlinx.coroutines.runBlocking
+import org.junit.Test
+import java.util.concurrent.atomic.AtomicInteger
+import kotlin.test.assertEquals
+
+@FlowPreview
+class FlowConcatArrayEagerTest {
+    @Test
+    fun basic() = runBlocking {
+        val state1 = AtomicInteger()
+        val state2 = AtomicInteger()
+        concatArrayEager(
+                range(1, 5).onStart {
+                    delay(200)
+                    state1.set(1)
+                }.onEach { println(it) },
+                range(6, 5).onStart {
+                    state2.set(state1.get())
+                }.onEach { println(it) },
+        )
+        .assertResult(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+
+        assertEquals(0, state2.get())
+    }
+
+    @Test
+    fun basic1() = runBlocking {
+        concatArrayEager(
+                range(1, 5)
+        )
+        .assertResult(1, 2, 3, 4, 5)
+
+    }
+
+    @Test
+    fun take() = runBlocking {
+        concatArrayEager(
+                range(1, 5).onStart { delay(100) },
+                range(6, 5)
+        )
+                .take(6)
+                .assertResult(1, 2, 3, 4, 5, 6)
+    }
+}

src/test/kotlin/hu/akarnokd/kotlin/flow/impl/FlowOnBackpressureDropTest.kt

@@ -17,8 +17,7 @@
 package hu.akarnokd.kotlin.flow.impl
 
 import hu.akarnokd.kotlin.flow.assertResult
-import hu.akarnokd.kotlin.flow.onBackpressurureDrop
-import hu.akarnokd.kotlin.flow.startCollectOn
+import hu.akarnokd.kotlin.flow.onBackpressureDrop
 import kotlinx.coroutines.*
 import kotlinx.coroutines.flow.*
 import org.junit.Test
@@ -35,7 +34,7 @@ class FlowOnBackpressureDropTest {
                 delay(100)
             }
         }
-        .onBackpressurureDrop()
+        .onBackpressureDrop()
         .map {
             delay(130)
             it