Make RibEvents buffer size configurable

android/libraries/rib-base/src/main/kotlin/com/uber/rib/core/RibEvents.kt

@@ -20,20 +20,52 @@ import io.reactivex.Observable
 import kotlinx.coroutines.channels.BufferOverflow
 import kotlinx.coroutines.channels.Channel
 import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.SharedFlow
+import kotlinx.coroutines.flow.asSharedFlow
 import kotlinx.coroutines.rx2.asObservable
 
 public object RibEvents {
+  private var extraBufferCapacity: Int = Channel.UNLIMITED
 
-  private val mutableRouterEvents =
-    MutableSharedFlow<RibRouterEvent>(0, Channel.UNLIMITED, BufferOverflow.DROP_OLDEST)
-  private val mutableRibDurationEvents =
-    MutableSharedFlow<RibActionInfo>(0, Channel.UNLIMITED, BufferOverflow.DROP_OLDEST)
+  /**
+   * Sets the extra buffer capacity for [routerEventsFlow] and [ribActionEventsFlow].
+   *
+   * This function must be called on the main thread, and before any usage of:
+   * 1. [routerEventsFlow]
+   * 2. [routerEvents]
+   * 3. [ribActionEventsFlow]
+   * 4. [ribActionEvents]
+   */
+  @JvmStatic
+  public fun setExtraBufferCapacity(capacity: Int) {
+    extraBufferCapacity = capacity
+  }
+
+  private val mutableRouterEvents by lazy {
+    MutableSharedFlow<RibRouterEvent>(0, extraBufferCapacity, BufferOverflow.DROP_OLDEST)
+  }
+
+  private val mutableRibDurationEvents by lazy {
+    MutableSharedFlow<RibActionInfo>(0, extraBufferCapacity, BufferOverflow.DROP_OLDEST)
+  }
+
+  @JvmStatic
+  public val routerEventsFlow: SharedFlow<RibRouterEvent> by lazy {
+    mutableRouterEvents.asSharedFlow()
+  }
 
   @JvmStatic
-  public val routerEvents: Observable<RibRouterEvent> = mutableRouterEvents.asObservable()
+  public val routerEvents: Observable<RibRouterEvent> by lazy { mutableRouterEvents.asObservable() }
 
   @JvmStatic
-  public val ribActionEvents: Observable<RibActionInfo> = mutableRibDurationEvents.asObservable()
+  public val ribActionEventsFlow: SharedFlow<RibActionInfo> by lazy {
+    mutableRibDurationEvents.asSharedFlow()
+  }
+
+  @JvmStatic
+  public val ribActionEvents: Observable<RibActionInfo> by lazy {
+    mutableRibDurationEvents.asObservable()
+  }
 
   /** Indicates if [ribActionEvents] will be emitting. */
   public var areRibActionEmissionsAllowed: Boolean = false

android/libraries/rib-base/src/test/kotlin/com/uber/rib/core/RibEventsTest.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2024. Uber Technologies
+ *
+ * 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 com.uber.rib.core
+
+import com.google.common.truth.Truth.assertThat
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.channels.Channel
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.runCurrent
+import kotlinx.coroutines.test.runTest
+import org.junit.After
+import org.junit.Before
+import org.junit.Ignore
+import org.junit.Test
+import org.mockito.kotlin.mock
+
+@OptIn(ExperimentalCoroutinesApi::class)
+@Ignore(
+  """
+    Test only passes when running in isolation: RibEvents flows might've been accessed
+    when running full suite.
+  """,
+)
+class RibEventsTest {
+  private val extraBufferCapacity = 16
+
+  @Before
+  fun setUp() {
+    RibEvents.setExtraBufferCapacity(extraBufferCapacity)
+  }
+
+  @After
+  fun tearDown() {
+    RibEvents.setExtraBufferCapacity(Channel.UNLIMITED)
+  }
+
+  @Test
+  fun setExtraBufferCapacityTest() = runTest {
+    val results = mutableListOf<RibRouterEvent>()
+    backgroundScope.launch { RibEvents.routerEventsFlow.collect(results::add) }
+    runCurrent()
+    repeat(32) { RibEvents.emitRouterEvent(RibEventType.ATTACHED, mock(), mock()) }
+    runCurrent()
+    assertThat(results.size).isEqualTo(16)
+  }
+}