Zustand 🐻 implementation for Kotlin :) https://github.com/pmndrs/zustand

ComposeStore.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */
 
private val LocalStore: ProvidableCompositionLocal<Store<*>> = compositionLocalOf { error("Store not provided") }

@Composable
fun <STATE : State> StoreProvider(store: Store<STATE>, content: @Composable Store<STATE>.() -> Unit) {
  CompositionLocalProvider(LocalStore provides store) {
    store.content()
  }
}

@Composable
@Suppress("UNCHECKED_CAST")
fun <STATE : State> store(): Store<STATE> = LocalStore.current as Store<STATE>

@Composable
inline fun <reified STATE : State> dispatcher(): (Effect<Store<STATE>, STATE>) -> Unit = store<STATE>().dispatcher()

@Composable
fun <STATE : State> Store<STATE>.dispatcher(): (Effect<Store<STATE>, STATE>) -> Unit = ::dispatch

@Composable
inline fun <reified STATE : State> multiDispatcher(): (Array<out Effect<Store<STATE>, STATE>>) -> Unit = store<STATE>().multiDispatcher()

@Composable
fun <STATE : State> Store<STATE>.multiDispatcher(): (Array<out Effect<Store<STATE>, STATE>>) -> Unit = ::dispatch

@Composable
inline fun <reified STATE : State, VALUE> subscribeTo(
  crossinline selector: @DisallowComposableCalls STATE.() -> VALUE
): MutableState<VALUE> = store<STATE>().subscribeTo(selector)

@Composable
inline fun <STATE : State, VALUE> Store<STATE>.subscribeTo(
  crossinline selector: @DisallowComposableCalls (STATE.() -> VALUE)
): MutableState<VALUE> {
  val result: MutableState<VALUE> = remember { mutableStateOf(state.selector()) }
  DisposableEffect(result) {
    val unsubscribe: Unsubscribe = subscribe { state -> result.value = state.selector() }
    onDispose(unsubscribe)
  }
  return result
}

@Composable
inline fun <reified STATE : State> subscribe(): MutableState<STATE> = store<STATE>().subscribe()

@Composable
fun <STATE : State> Store<STATE>.subscribe(): MutableState<STATE> {
  val result: MutableState<STATE> = remember { mutableStateOf(state) }
  DisposableEffect(result) {
    val unsubscribe: Unsubscribe = subscribe { state -> result.value = state }
    onDispose(unsubscribe)
  }
  return result
}

ComposeStoreTest.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */

@OptIn(ExperimentalCoroutinesApi::class)
@RunWith(AndroidJUnit4::class)
class ComposeStoreTest {
  @get:Rule
  val compose = createComposeRule()

  @Test
  fun test_initial_subscribeTo() = runTest {
    val store = createTestStore(initialState = TestState(counter = 100, other = 200))
    compose.setContent {
      StoreProvider(store) {
        val counter by subscribeTo { counter }
        val other by subscribeTo { other }
        assertThat(counter).isEqualTo(store.state.counter)
        assertThat(other).isEqualTo(store.state.other)
      }
    }
    compose.awaitIdle()
  }

  @Test
  fun test_dispatch_and_subscribeTo() = runTest {
    val store = createTestStore(initialState = TestState(counter = 100, other = 200))
    compose.setContent {
      StoreProvider(store) {
        val counter by subscribeTo { counter }
        val dispatch = dispatcher()
        Button(
          onClick = { dispatch(::incrementCounterByOneEffect) },
          modifier = Modifier.testTag("button"),
        ) {
          Text("$counter")
        }
      }
    }
    compose.awaitIdle()
    assert(store)
  }

  @Test
  fun test_dispatch_and_subscribe_to_all() = runTest {
    val store = createTestStore(initialState = TestState(counter = 100, other = 200))
    compose.setContent {
      StoreProvider(store) {
        val state by subscribe()
        val dispatch = dispatcher()
        Button(
          onClick = { dispatch(::incrementCounterByOneEffect) },
          modifier = Modifier.testTag("button"),
        ) {
          Text("${state.counter}")
        }
      }
    }
    compose.awaitIdle()
    assert(store)
  }

  private suspend fun assert(store: Store<TestState>) {
    compose.onNodeWithTag("button").run {
      val counter = store.state.counter
      assertTextEquals("$counter")
      performClick()
      compose.awaitIdle()
      assertTextEquals("${counter?.plus(1)}")
    }
  }
}

SameThreadEnforcedStoreTest.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */
 
 @OptIn(ExperimentalCoroutinesApi::class)
class SameThreadEnforcedStoreTest {
  @Test(expected = IllegalStateException::class)
  fun `dispatch an Effect from a thread other than thread from which the SameThreadEnforcedStore was created will throw an IllegalStateException`() {
    val sameThreadEnforcedStore = createSameThreadEnforcedStore(createTestStore())
    val storeThread = currentThreadName()
    runTest {
      withContext(Dispatchers.Default) {
        assertThat(storeThread).isNotEqualTo(currentThreadName())
        sameThreadEnforcedStore.dispatch(::incrementCounterByOneEffect)
      }
    }
  }

  @Test
  fun `dispatch an Effect from a thread other than thread from which the Store was created will not throw an exception`() {
    val store = createTestStore()
    val storeThread = currentThreadName()
    runTest {
      withContext(Dispatchers.Default) {
        assertThat(storeThread).isNotEqualTo(currentThreadName())
        store.dispatch(::incrementCounterByOneEffect)
      }
    }
  }
}

private fun currentThreadName(): String = Thread.currentThread().name

Store.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */

interface State
typealias STORE<STATE> = Store<STATE>

typealias Effect<STORE, STATE> = (store: STORE, mutate: Mutator<STATE>) -> Unit
typealias EffectWith<STORE, STATE, PARAMS> = (params: PARAMS, store: STORE, mutate: Mutator<STATE>) -> Unit

typealias Mutator<STATE> = (STATE) -> Unit

typealias Subscription<STATE> = (state: STATE) -> Unit
typealias Unsubscribe = () -> Unit

private class SubscriptionWithBinder<STATE>(val binder: Binder<STATE>, val subscription: Subscription<STATE>?) {
  operator fun component1() = binder
  operator fun component2() = subscription
}

typealias Binder<STATE> = STATE.() -> Any?

@Suppress("UnusedPrivateMember")
private fun <STATE> defaultBinder(bind: STATE): Int = bind.hashCode()

typealias SideEffect<STATE> = Effect<STORE<STATE>, STATE>

interface Store<STATE : State> {
  val state: STATE
  fun subscribe(subscription: Subscription<STATE>): Unsubscribe
  fun subscribe(binder: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe
  fun subscribe(vararg binders: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe
  fun dispatch(effect: Effect<Store<STATE>, STATE>)
  fun dispatch(vararg effects: Effect<Store<STATE>, STATE>)
  fun <PARAMS> dispatch(effect: EffectWith<Store<STATE>, STATE, PARAMS>, params: PARAMS)
  fun <PARAMS> dispatch(effects: Map<EffectWith<Store<STATE>, STATE, PARAMS>, PARAMS>)
  fun rehydrate(newState: STATE)
}

fun <STATE : State> createStore(
  initialState: STATE,
  vararg sideEffects: SideEffect<STATE>
): Store<STATE> = object : Store<STATE> {
  private val _state: AtomicReference<STATE> = AtomicReference(initialState)
  override val state: STATE get() = _state.get()
  private val subscriptions = CopyOnWriteArrayList<SubscriptionWithBinder<STATE>>()

  override fun subscribe(subscription: Subscription<STATE>): Unsubscribe = subscribe(::defaultBinder, subscription)
  override fun subscribe(binder: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe {
    val subscriptionWithBinder = SubscriptionWithBinder(binder, subscription)
    subscriptions.add(subscriptionWithBinder)
    subscription(state)
    return { subscriptions.remove(subscriptionWithBinder) }
  }

  override fun subscribe(vararg binders: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe {
    fun consumer(subscriptions: List<Unsubscribe>): Unsubscribe = { subscriptions.forEach { it() } }
    return consumer(binders.map { subscribe(it, subscription) })
  }

  override fun dispatch(effect: Effect<Store<STATE>, STATE>) = effect(this, ::mutate)
  override fun dispatch(vararg effects: Effect<Store<STATE>, STATE>) = listOf(*effects).forEach { effect -> effect(this, ::mutate) }
  override fun <PARAMS> dispatch(effect: EffectWith<Store<STATE>, STATE, PARAMS>, params: PARAMS) = effect(params, this, ::mutate)
  override fun <PARAMS> dispatch(effects: Map<EffectWith<Store<STATE>, STATE, PARAMS>, PARAMS>) = effects.forEach { (effect, params) ->
    effect(params, this, ::mutate)
  }

  private fun mutate(newState: STATE) {
    fun emit(newState: STATE) = subscriptions
      .reversed()
      .filter { (binder, _) -> state.binder() !== newState.binder() }
      .forEach { (_, subscription) -> subscription?.invoke(newState) }
      .also { _state.set(newState) }
    emit(newState)
    sideEffects.forEach { sideEffect -> sideEffect(this, ::emit) }
  }

  override fun rehydrate(newState: STATE) = mutate(newState)
}

StoreTest.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */
 
class StoreTest {
  private val store: Store<TestState> = createTestStore()
  private var notified = false

  @Test
  fun `Effect dispatching`() {
    fun effect(store: Store<TestState>, mutate: Mutator<TestState>) {
      mutate(store.state.copy(counter = 100))
      assertThat(store.state.counter).isEqualTo(100)
      mutate(store.state.copy(counter = 200))
      assertThat(store.state.counter).isEqualTo(200)
    }
    store.dispatch(::effect)
  }

  @Test
  fun `Effect dispatching with params`() {
    class Params(val value: Int)

    fun effect(params: Params, store: Store<TestState>, mutate: Mutator<TestState>) {
      mutate(store.state.copy(counter = 100 + params.value))
      assertThat(store.state.counter).isEqualTo(100 + params.value)
      mutate(store.state.copy(counter = 200 + params.value))
      assertThat(store.state.counter).isEqualTo(200 + params.value)
    }
    store.dispatch(::effect, Params(1))
  }

  @Test
  @Suppress("UnusedPrivateMember")
  fun `Effect dispatching with SideEffects`() {
    fun sideEffect(store: Store<TestState>, mutate: Mutator<TestState>) {
      assertThat(store.state.counter).isEqualTo(100)
    }

    fun effect(store: Store<TestState>, mutate: Mutator<TestState>) {
      mutate(store.state.copy(counter = 100))
    }
    createTestStore(TestState(), ::sideEffect).dispatch(::effect)
  }

  @Test
  fun `get initial status upon subscription`() {
    store.subscribe { state ->
      notified = true
      assertThat(state.counter).isNull()
    }
    assertThat(notified).isTrue
  }

  @Test
  fun `Subscribe with no binding`() {
    store.run {
      subscribe { state ->
        notified = true
        // discard initial status
        state.counter?.let { assertThat(state.counter).isEqualTo(1) }
      }
      dispatch(::incrementCounterByOneEffect)
    }
    assertThat(notified).isTrue
  }

  @Test
  fun `Subscribe with binding`() {
    store.run {
      subscribe({ other }) { state ->
        notified = true
        // discard initial status
        state.other?.let { assertThat(state.other).isEqualTo(1) }
        assertThat(state.counter).isNull()
      }
      dispatch(::incrementOtherByOneEffect)
    }
    assertThat(notified).isTrue
  }

  @Test
  fun `Subscribe with a list of bindings`() {
    store.run {
      subscribe({ other }, { counter }) { state ->
        notified = true
        state.other?.let { assertThat(state.other).isEqualTo(1) }
        assertThat(state.counter).isNull()
      }
      dispatch(::incrementOtherByOneEffect)
    }
    assertThat(notified).isTrue
  }

  @Test
  fun `rehydrate state`() {
    store.run {
      subscribe { state ->
        notified = true
        state.counter?.let { assertThat(state.counter).isEqualTo(100) }
      }
      rehydrate(TestState(counter = 100))
      assertThat(state.counter).isEqualTo(100)
    }
    assertThat(notified).isTrue
  }
}

TestEffectStore.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */
 
 data class TestState(
  val counter: Int? = null,
  val other: Int? = null
) : State

fun createTestStore(initialState: TestState = TestState(), vararg sideEffects: SideEffect<TestState>) = createStore(
  initialState = initialState,
  sideEffects = sideEffects
)

fun incrementCounterByOneEffect(store: Store<TestState>, mutate: Mutator<TestState>) {
  mutate(store.state.copy(counter = (store.state.counter ?: 0) + 1))
}

TestState.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */
 
 data class TestState(
  val counter: Int? = null,
  val other: Int? = null
) : State

fun createTestStore(initialState: TestState = TestState(), vararg sideEffects: SideEffect<TestState>) = createStore(
  initialState = initialState,
  sideEffects = sideEffects
)

fun incrementCounterByOneEffect(store: Store<TestState>, mutate: Mutator<TestState>) {
  mutate(store.state.copy(counter = (store.state.counter ?: 0) + 1))
}

fun incrementOtherByOneEffect(store: Store<TestState>, mutate: Mutator<TestState>) {
  mutate(store.state.copy(other = (store.state.other ?: 0) + 1))
}

ThreadSafeStore.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */

/**
 * Threadsafe decorator that synchronizes access to each function
 * This may have performance impact on JVM/Native.
 */
fun <STATE : State> createThreadSafeStore(store: Store<STATE>): ThreadSafeStore<STATE> = ThreadSafeStore(store)
fun <STATE : State> createThreadSafeStore(
  initialState: STATE,
  vararg sideEffects: SideEffect<STATE>
): ThreadSafeStore<STATE> = ThreadSafeStore(createStore(initialState, *sideEffects))

class ThreadSafeStore<STATE : State>(private val store: Store<STATE>) : Store<STATE> by store {
  @get:Synchronized
  override val state get() = synchronized(this) { store.state }

  @Synchronized
  override fun subscribe(subscription: Subscription<STATE>): Unsubscribe = synchronized(this) { store.subscribe(subscription) }

  @Synchronized
  override fun subscribe(binder: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe =
    synchronized(this) { store.subscribe(binder, subscription) }

  @Synchronized
  override fun subscribe(vararg binders: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe =
    synchronized(this) { store.subscribe(binders = binders, subscription) }

  @Synchronized
  override fun dispatch(effect: Effect<Store<STATE>, STATE>) = synchronized(this) { store.dispatch(effect) }

  @Synchronized
  override fun dispatch(vararg effects: Effect<Store<STATE>, STATE>) = synchronized(this) { store.dispatch(effects = effects) }

  @Synchronized
  override fun <PARAMS> dispatch(effect: EffectWith<Store<STATE>, STATE, PARAMS>, params: PARAMS) = synchronized(this) { store.dispatch(effect, params) }

  @Synchronized
  override fun <PARAMS> dispatch(effects: Map<EffectWith<Store<STATE>, STATE, PARAMS>, PARAMS>) = synchronized(this) { store.dispatch(effects) }

  @Synchronized
  override fun rehydrate(newState: STATE) = synchronized(this) { store.rehydrate(newState) }
}

/**
 * Decorator for store whose functions can only be accessed from the same thread in which the Store was created
 * Functions called from a thread other than thread from which the Store was created will throw an IllegalStateException
 */
fun <STATE : State> createSameThreadEnforcedStore(store: Store<STATE>): SameThreadEnforcedStore<STATE> = SameThreadEnforcedStore(store)
fun <STATE : State> createSameThreadEnforcedStore(
  initialState: STATE,
  vararg sideEffects: SideEffect<STATE>
): SameThreadEnforcedStore<STATE> = SameThreadEnforcedStore(createStore(initialState, *sideEffects))

class SameThreadEnforcedStore<STATE : State>(private val store: Store<STATE>) : Store<STATE> by store {
  private val storeThreadName = currentThreadName()

  override fun subscribe(subscription: Subscription<STATE>): Unsubscribe {
    checkIsSameThread()
    return store.subscribe(subscription)
  }

  override fun subscribe(binder: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe {
    checkIsSameThread()
    return store.subscribe(binder, subscription)
  }

  override fun subscribe(vararg binders: Binder<STATE>, subscription: Subscription<STATE>): Unsubscribe {
    checkIsSameThread()
    return store.subscribe(binders = binders, subscription)
  }

  override fun dispatch(effect: Effect<Store<STATE>, STATE>) {
    checkIsSameThread()
    return store.dispatch(effect)
  }

  override fun dispatch(vararg effects: Effect<Store<STATE>, STATE>) {
    checkIsSameThread()
    return store.dispatch(effects = effects)
  }

  override fun <PARAMS> dispatch(effect: EffectWith<Store<STATE>, STATE, PARAMS>, params: PARAMS) {
    checkIsSameThread()
    return store.dispatch(effect, params)
  }

  override fun <PARAMS> dispatch(effects: Map<EffectWith<Store<STATE>, STATE, PARAMS>, PARAMS>) {
    checkIsSameThread()
    return store.dispatch(effects)
  }

  override fun rehydrate(newState: STATE) {
    checkIsSameThread()
    return store.rehydrate(newState)
  }

  private fun currentThreadName(): String = Thread.currentThread().name.stripCoroutineName()
  private fun isSameThread() = storeThreadName.equals(currentThreadName(), ignoreCase = true)
  private fun checkIsSameThread() = check(isSameThread()) {
    """You may not call the store from a thread other than the thread on which it was created.
       This store was created on: '$storeThreadName' and current thread is '${currentThreadName()}'
    """.trimMargin()
  }

  /**
   * Thread name may have '@coroutine#n' appended to it
   * https://kotlinlang.org/docs/coroutine-context-and-dispatchers.html#debugging-using-logging
   */
  private fun String.stripCoroutineName(): String {
    val lastIndex = this.lastIndexOf('@')
    return (if (lastIndex < 0) this else this.substring(0, lastIndex)).trim()
  }
}

ThreadSafeStoreTest.kt

/*
 * Copyright (c) 2022. Héctor de Isidro - hector6872
 *
 * 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.
 */
 
 /**
 * test results (performance impact example):
 *   thread safe: completed 100000 actions in 48 ms
 *   non-thread safe: completed 100000 actions in 24 ms
 */
@OptIn(ExperimentalCoroutinesApi::class)
class ThreadSafeStoreTest {
  @Test
  fun `massive Effect dispatching using a non-thread safe Store should return an unexpected state`() {
    val store = createTestStore()
    runTest {
      withContext(Dispatchers.Default) {
        massiveRunner(
          "non-thread safe",
          SYNC_NUM_COROUTINES,
          SYNC_NUM_REPEATS
        ) { store.dispatch(::incrementCounterByOneEffect) }
        assertThat(store.state.counter).isNotEqualTo(SYNC_NUM_COROUTINES * SYNC_NUM_REPEATS)
      }
    }
  }

  @Test
  fun `massive Effect dispatching using a thread safe Store should return an expected state`() {
    val threadSafeStore = createThreadSafeStore(createTestStore())
    runTest {
      withContext(Dispatchers.Default) {
        massiveRunner(
          "thread safe",
          SYNC_NUM_COROUTINES,
          SYNC_NUM_REPEATS
        ) { threadSafeStore.dispatch(::incrementCounterByOneEffect) }
        assertThat(threadSafeStore.state.counter).isEqualTo(SYNC_NUM_COROUTINES * SYNC_NUM_REPEATS)
      }
    }
  }
}

private suspend fun massiveRunner(tag: String, numCoroutines: Int, numRepeats: Int, block: suspend () -> Unit) {
  val time = measureTimeMillis {
    coroutineScope {
      repeat(numCoroutines) {
        launch {
          repeat(numRepeats) { block() }
        }
      }
    }
  }
  println("$tag: completed ${numCoroutines * numRepeats} actions in $time ms")
}