Add a default CoroutineContext to rxFlowable

Author: PhilGlass

reactive/kotlinx-coroutines-rx2/src/main/kotlin/kotlinx/coroutines/experimental/rx2/RxFlowable.kt

@@ -17,13 +17,18 @@
 package kotlinx.coroutines.experimental.rx2
 
 import io.reactivex.Flowable
+import kotlinx.coroutines.experimental.CoroutineDispatcher
+import kotlinx.coroutines.experimental.CoroutineScope
+import kotlinx.coroutines.experimental.DefaultDispatcher
+import kotlinx.coroutines.experimental.Job
 import kotlinx.coroutines.experimental.channels.ProducerScope
 import kotlinx.coroutines.experimental.reactive.publish
+import kotlin.coroutines.experimental.ContinuationInterceptor
 import kotlin.coroutines.experimental.CoroutineContext
 
 /**
  * Creates cold [flowable][Flowable] that will run a given [block] in a coroutine.
- * Every time the returned flowable is subscribed, it starts a new coroutine in the specified [context].
+ * Every time the returned flowable is subscribed, it starts a new coroutine.
  * Coroutine emits items with `send`. Unsubscribing cancels running coroutine.
  *
  * Invocations of `send` are suspended appropriately when subscribers apply back-pressure and to ensure that
@@ -34,8 +39,18 @@ import kotlin.coroutines.experimental.CoroutineContext
  * | `send`                                       | `onNext`
  * | Normal completion or `close` without cause   | `onComplete`
  * | Failure with exception or `close` with cause | `onError`
+ *
+ * The [context] for the new coroutine can be explicitly specified.
+ * See [CoroutineDispatcher] for the standard context implementations that are provided by `kotlinx.coroutines`.
+ * The [context][CoroutineScope.context] of the parent coroutine from its [scope][CoroutineScope] may be used,
+ * in which case the [Job] of the resulting coroutine is a child of the job of the parent coroutine.
+ * If the context does not have any dispatcher nor any other [ContinuationInterceptor], then [DefaultDispatcher] is used.
+ *
+ * @param context context of the coroutine. The default value is [DefaultDispatcher].
+ * @param block the coroutine code.
  */
+@JvmOverloads // for binary compatibility with older code compiled before context had a default
 public fun <T> rxFlowable(
-    context: CoroutineContext,
+    context: CoroutineContext = DefaultDispatcher,
     block: suspend ProducerScope<T>.() -> Unit
 ): Flowable<T> = Flowable.fromPublisher(publish(context, block))