Add channel benchmarks

benchmarks/src/jmh/kotlin/benchmarks/ChannelBenchmark.kt

@@ -0,0 +1,143 @@
+package benchmarks
+
+import kotlinx.coroutines.*
+import kotlinx.coroutines.channels.*
+import org.openjdk.jmh.annotations.*
+import java.util.concurrent.*
+
+@Warmup(iterations = 7, time = 1)
+@Measurement(iterations = 10, time = 1)
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+@Fork(1)
+open class ChannelBenchmark {
+    // max coroutines launched per benchmark
+    // to allow for true parallelism
+    val cores = Runtime.getRuntime().availableProcessors()
+
+    //                4 KB,   40 KB,   400 KB,      4 MB,      40 MB,      400 MB
+    @Param(value = ["1000", "10000", "100000", "1000000", "10000000", "100000000"])
+    var count: Int = 0
+
+    // 1. Preallocate.
+    // 2. Different values to avoid helping the cache.
+    val list = List(100000000) { it }
+
+    @State(Scope.Benchmark)
+    open class UnlimitedChannelWrapper {
+        //                0,      4 MB,      40 MB,      400 MB
+        @Param(value = ["0", "1000000", "10000000", "100000000"])
+        private var prefill = 0
+
+        lateinit var channel: Channel<Int>
+
+        val list = List(100000000) { it }
+
+        @Setup(Level.Invocation)
+        fun createPrefilledChannel() {
+            channel = Channel(Channel.UNLIMITED)
+            repeat(prefill) {
+                channel.trySend(list[it])
+            }
+        }
+    }
+
+
+    @Benchmark
+    fun sendUnlimited() = runBlocking {
+        runSend(count, Channel.UNLIMITED)
+    }
+
+    @Benchmark
+    fun sendConflated() = runBlocking {
+        runSend(count, Channel.CONFLATED)
+    }
+
+    @Benchmark
+    fun sendReceiveUnlimited(wrapper: UnlimitedChannelWrapper) = runBlocking {
+        runSendReceive(wrapper.channel, count)
+    }
+
+    @Benchmark
+    fun sendReceiveConflated() = runBlocking(Dispatchers.Default) {
+        runSendReceive(Channel(Channel.CONFLATED), count)
+    }
+
+    @Benchmark
+    fun sendReceiveRendezvous() = runBlocking(Dispatchers.Default) {
+        // NB: Rendezvous is partly benchmarking the scheduler, not the channel alone.
+        // So don't trust the Rendezvous results too much.
+        runSendReceive(Channel(Channel.RENDEZVOUS), count)
+    }
+
+    @Benchmark
+    fun oneSenderManyReceivers(wrapper: UnlimitedChannelWrapper) = runBlocking {
+        runSendReceive(wrapper.channel, count, 1, cores - 1)
+    }
+
+    @Benchmark
+    fun manySendersOneReceiver(wrapper: UnlimitedChannelWrapper) = runBlocking {
+        runSendReceive(wrapper.channel, count, cores - 1, 1)
+    }
+
+    @Benchmark
+    fun manySendersManyReceivers(wrapper: UnlimitedChannelWrapper) = runBlocking {
+        runSendReceive(wrapper.channel, count, cores / 2, cores / 2)
+    }
+
+    private suspend fun runSend(count: Int, capacity: Int) {
+        val channel = Channel<Int>(capacity)
+        repeat(count) {
+            channel.send(list[it])
+        }
+    }
+
+    suspend fun <E> Channel<E>.forEach(action: (E) -> Unit) {
+        for (element in this) {
+            action(element)
+        }
+    }
+
+    // NB: not all parameter combinations make sense in general.
+    // E.g., for the rendezvous channel, senders should be equal to receivers.
+    // If they are non-equal, it's a special case of performance under contention.
+    private suspend inline fun runSendReceive(channel: Channel<Int>, count: Int, senders: Int = 1, receivers: Int = 1) {
+        //require (senders > 0 && receivers > 0)
+        //require (senders + receivers <= cores) // Can be used with more than num cores, but what would it measure?
+        // if the channel is prefilled, only receive the items that were sent by this function
+        val receiveAll = channel.isEmpty
+        // send almost `count` items, up to `senders - 1` items will not be sent (negligible)
+        val countPerSender = count / senders
+        // for prefilled channel only: up to `receivers - 1` items of the sent items will not be received
+        // (on top of the prefilled items which we do not aim to receive at all) (negligible)
+        val countPerReceiverAtLeast = countPerSender * senders / receivers
+        withContext(Dispatchers.Default) {
+            repeat(receivers) {
+                launch {
+                    if (receiveAll) {
+                        channel.forEach {
+                            // possibly receive into the blackhole
+                        }
+                    } else {
+                       repeat(countPerReceiverAtLeast) {
+                           // possibly receive into the blackhole
+                           channel.receive()
+                       }
+                    }
+                }
+            }
+
+            coroutineScope {
+                repeat(senders) {
+                    launch {
+                        repeat(countPerSender) {
+                            channel.send(list[it])
+                        }
+                    }
+                }
+            }
+            channel.close()
+        }
+    }
+}