fix: Amplitude.build() is not main thread safe on Android (#55)

* put disk reads in coroutines

* move storage to build() to avoid disk read on main thread when init

* add isBuilt to core and check before set userid using idContainer

android/src/main/java/com/amplitude/android/Amplitude.kt

@@ -12,6 +12,7 @@ import com.amplitude.id.FileIdentityStorageProvider
 import com.amplitude.id.IdentityConfiguration
 import com.amplitude.id.IdentityContainer
 import com.amplitude.id.IdentityUpdateType
+import kotlinx.coroutines.async
 import kotlinx.coroutines.launch
 
 open class Amplitude(
@@ -27,36 +28,33 @@ open class Amplitude(
     private lateinit var androidContextPlugin: AndroidContextPlugin
 
     override fun build() {
-        val storageDirectory = (configuration as Configuration).context.getDir("${FileStorage.STORAGE_PREFIX}-${configuration.instanceName}", Context.MODE_PRIVATE)
-        idContainer = IdentityContainer.getInstance(
-            IdentityConfiguration(
-                instanceName = configuration.instanceName,
-                apiKey = configuration.apiKey,
-                identityStorageProvider = FileIdentityStorageProvider(),
-                storageDirectory = storageDirectory
+        val client = this
+        isBuilt = amplitudeScope.async(amplitudeDispatcher) {
+            storage = configuration.storageProvider.getStorage(client)
+            val storageDirectory = (configuration as Configuration).context.getDir("${FileStorage.STORAGE_PREFIX}-${configuration.instanceName}", Context.MODE_PRIVATE)
+            idContainer = IdentityContainer.getInstance(
+                IdentityConfiguration(
+                    instanceName = configuration.instanceName,
+                    apiKey = configuration.apiKey,
+                    identityStorageProvider = FileIdentityStorageProvider(),
+                    storageDirectory = storageDirectory
+                )
             )
-        )
-        val listener = AnalyticsIdentityListener(store)
-        idContainer.identityManager.addIdentityListener(listener)
-        if (idContainer.identityManager.isInitialized()) {
-            listener.onIdentityChanged(idContainer.identityManager.getIdentity(), IdentityUpdateType.Initialized)
-        }
-        amplitudeScope.launch(amplitudeDispatcher) {
-            previousSessionId = storage.read(Storage.Constants.PREVIOUS_SESSION_ID) ?.let {
-                it.toLong()
-            } ?: -1
+            val listener = AnalyticsIdentityListener(store)
+            idContainer.identityManager.addIdentityListener(listener)
+            if (idContainer.identityManager.isInitialized()) {
+                listener.onIdentityChanged(idContainer.identityManager.getIdentity(), IdentityUpdateType.Initialized)
+            }
+            previousSessionId = storage.read(Storage.Constants.PREVIOUS_SESSION_ID)?.toLong() ?: -1
             if (previousSessionId >= 0) {
                 sessionId = previousSessionId
             }
-            lastEventId = storage.read(Storage.Constants.LAST_EVENT_ID) ?. let {
-                it.toLong()
-            } ?: 0
-            lastEventTime = storage.read(Storage.Constants.LAST_EVENT_TIME) ?. let {
-                it.toLong()
-            } ?: -1
+            lastEventId = storage.read(Storage.Constants.LAST_EVENT_ID)?.toLong() ?: 0
+            lastEventTime = storage.read(Storage.Constants.LAST_EVENT_TIME)?.toLong() ?: -1
             androidContextPlugin = AndroidContextPlugin()
             add(androidContextPlugin)
             add(AndroidLifecyclePlugin())
+            true
         }
         add(AmplitudeDestination())
     }

android/src/test/java/com/amplitude/android/AmplitudeTest.kt

@@ -47,15 +47,17 @@ class AmplitudeTest {
         amplitudeDispatcherField.isAccessible = true
         amplitudeDispatcherField.set(amplitude, dispatcher)
 
-        amplitude?.setUserId("test user")
-        amplitude?.setDeviceId("test device")
-        advanceUntilIdle()
-        Assertions.assertEquals("test user", amplitude?.store?.userId)
-        Assertions.assertEquals("test device", amplitude?.store?.deviceId)
+        if (amplitude?.isBuilt!!.await()) {
+            amplitude?.setUserId("test user")
+            amplitude?.setDeviceId("test device")
+            advanceUntilIdle()
+            Assertions.assertEquals("test user", amplitude?.store?.userId)
+            Assertions.assertEquals("test device", amplitude?.store?.deviceId)
 
-        amplitude?.reset()
-        advanceUntilIdle()
-        Assertions.assertNull(amplitude?.store?.userId)
-        Assertions.assertNotEquals("test device", amplitude?.store?.deviceId)
+            amplitude?.reset()
+            advanceUntilIdle()
+            Assertions.assertNull(amplitude?.store?.userId)
+            Assertions.assertNotEquals("test device", amplitude?.store?.deviceId)
+        }
     }
 }

core/src/main/java/com/amplitude/core/Amplitude.kt

@@ -24,8 +24,10 @@ import com.amplitude.id.IdentityContainer
 import com.amplitude.id.IdentityUpdateType
 import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.CoroutineScope
+import kotlinx.coroutines.Deferred
 import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.asCoroutineDispatcher
+import kotlinx.coroutines.async
 import kotlinx.coroutines.launch
 import java.util.UUID
 import java.util.concurrent.Executors
@@ -45,14 +47,14 @@ open class Amplitude internal constructor(
     val retryDispatcher: CoroutineDispatcher = Executors.newSingleThreadExecutor().asCoroutineDispatcher()
 ) {
     internal val timeline: Timeline
-    val storage: Storage
+    lateinit var storage: Storage
     val logger: Logger
     protected lateinit var idContainer: IdentityContainer
+    lateinit var isBuilt: Deferred<Boolean>
 
     init {
         require(configuration.isValid()) { "invalid configuration" }
         timeline = Timeline().also { it.amplitude = this }
-        storage = configuration.storageProvider.getStorage(this)
         logger = configuration.loggerProvider.getLogger(this)
         build()
     }
@@ -63,6 +65,7 @@ open class Amplitude internal constructor(
     constructor(configuration: Configuration) : this(configuration, State())
 
     open fun build() {
+        storage = configuration.storageProvider.getStorage(this)
         idContainer = IdentityContainer.getInstance(IdentityConfiguration(instanceName = configuration.instanceName, apiKey = configuration.apiKey, identityStorageProvider = IMIdentityStorageProvider()))
         val listener = AnalyticsIdentityListener(store)
         idContainer.identityManager.addIdentityListener(listener)
@@ -73,7 +76,8 @@ open class Amplitude internal constructor(
         add(ContextPlugin())
         add(AmplitudeDestination())
 
-        amplitudeScope.launch(amplitudeDispatcher) {
+        isBuilt = amplitudeScope.async(amplitudeDispatcher) {
+            true
         }
     }
 
@@ -166,7 +170,9 @@ open class Amplitude internal constructor(
      */
     fun setUserId(userId: String?): Amplitude {
         amplitudeScope.launch(amplitudeDispatcher) {
-            idContainer.identityManager.editIdentity().setUserId(userId).commit()
+            if (isBuilt.await()) {
+                idContainer.identityManager.editIdentity().setUserId(userId).commit()
+            }
         }
         return this
     }