feat: Interpolate machine state and task progress (#21)

This pull request implements interpolation of task progress
(represented as the `TaskState` and `MachineState` class) via the
Interpolation helpers implemented in #20. The model assumes that tasks progress
linearly between two measurements (since the time between measurements is
usually small).

2 files changed, 58 insertions, 2 deletions

diff --git a/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Helpers.kt b/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Helpers.kt
new file mode 100644
index 00000000..d6cf2e3a
--- /dev/null
+++ b/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Helpers.kt
@@ -0,0 +1,48 @@
+package com.atlarge.opendc.simulator.instrumentation
+
+import kotlinx.coroutines.experimental.Unconfined
+import kotlinx.coroutines.experimental.channels.ReceiveChannel
+import kotlinx.coroutines.experimental.channels.consumeEach
+import kotlinx.coroutines.experimental.channels.produce
+import kotlinx.coroutines.experimental.channels.toChannel
+import kotlinx.coroutines.experimental.launch
+import kotlin.coroutines.experimental.CoroutineContext
+
+/**
+ * Transform each element in the channel into a [ReceiveChannel] of output elements that is then flattened into the
+ * output stream by emitting elements from the channels as they become available.
+ *
+ * @param context The [CoroutineContext] to run the operation in.
+ * @param transform The function to transform the elements into channels.
+ * @return The flattened [ReceiveChannel] of merged elements.
+ */
+fun <E, R> ReceiveChannel<E>.flatMapMerge(context: CoroutineContext = Unconfined,
+                                          transform: suspend (E) -> ReceiveChannel<R>): ReceiveChannel<R> =
+    produce(context) {
+        val job = launch(Unconfined) {
+            consumeEach {
+                launch(coroutineContext) {
+                    transform(it).toChannel(this@produce)
+                }
+            }
+        }
+        job.join()
+    }
+
+/**
+ * Merge this channel with the other channel into an output stream by emitting elements from the channels as they
+ * become available.
+ *
+ * @param context The [CoroutineContext] to run the operation in.
+ * @param other The other channel to merge with.
+ * @return The [ReceiveChannel] of merged elements.
+ */
+fun <E, E1: E, E2: E> ReceiveChannel<E1>.merge(context: CoroutineContext = Unconfined,
+                                               other: ReceiveChannel<E2>): ReceiveChannel<E> =
+    produce(context) {
+        val job = launch(Unconfined) {
+            launch(coroutineContext) { toChannel(this@produce) }
+            launch(coroutineContext) { other.toChannel(this@produce) }
+        }
+        job.join()
+    }
diff --git a/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Interpolation.kt b/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Interpolation.kt
index 439813e8..5a033ff3 100644
--- a/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Interpolation.kt
+++ b/opendc-stdlib/src/main/kotlin/com/atlarge/opendc/simulator/instrumentation/Interpolation.kt
@@ -41,8 +41,15 @@ import kotlin.coroutines.experimental.CoroutineContext
  * @param interpolator A function to interpolate between the two element occurrences.
  */
 fun <E> ReceiveChannel<E>.interpolate(n: Int, context: CoroutineContext = Unconfined,
-                                      interpolator: (Double, E, E) -> E): ReceiveChannel<E> =
-    produce(context) {
+                                      interpolator: (Double, E, E) -> E): ReceiveChannel<E> {
+    require(n >= 0) { "The amount to interpolate must be non-negative" }
+
+    // If we do not want to interpolate any elements, just return the original channel
+    if (n == 0) {
+        return this
+    }
+
+    return produce(context) {
         consume {
             val iterator = iterator()
 
@@ -62,6 +69,7 @@ fun <E> ReceiveChannel<E>.interpolate(n: Int, context: CoroutineContext = Unconf
             }
         }
     }
+}
 
 /**
  * Perform a linear interpolation on the given double values.