Register executors as components.

The intent for those is to be used by all Firebase SDKs and forbid
creating their own at will.

Author: vkryachko

firebase-annotations/firebase-annotations.gradle

@@ -29,3 +29,7 @@ java {
 tasks.withType(JavaCompile) {
     options.compilerArgs << "-Werror"
 }
+
+dependencies {
+    implementation 'javax.inject:javax.inject:1'
+}

firebase-annotations/src/main/java/com/google/firebase/annotations/concurrent/Background.java

@@ -0,0 +1,14 @@
+package com.google.firebase.annotations.concurrent;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+/**
+ * An executor/coroutine dispatcher for long running tasks including disk IO, heavy CPU
+ * computations.
+ */
+@Qualifier
+@Target({ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD})
+public @interface Background {}

firebase-annotations/src/main/java/com/google/firebase/annotations/concurrent/Blocking.java

@@ -0,0 +1,14 @@
+package com.google.firebase.annotations.concurrent;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+/**
+ * An executor/coroutine dispatcher for tasks that can block for long periods of time, e.g network
+ * IO.
+ */
+@Qualifier
+@Target({ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD})
+public @interface Blocking {}

firebase-annotations/src/main/java/com/google/firebase/annotations/concurrent/Lightweight.java

@@ -0,0 +1,13 @@
+package com.google.firebase.annotations.concurrent;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+/**
+ * An executor/coroutine dispatcher for lightweight tasks that never block(on IO or other tasks).
+ */
+@Qualifier
+@Target({ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD})
+public @interface Lightweight {}

firebase-annotations/src/main/java/com/google/firebase/annotations/concurrent/UiThread.java

@@ -0,0 +1,11 @@
+package com.google.firebase.annotations.concurrent;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Target;
+
+import javax.inject.Qualifier;
+
+/** An executor/coroutine dispatcher for work that must run on the UI thread. */
+@Qualifier
+@Target({ElementType.PARAMETER, ElementType.METHOD, ElementType.FIELD})
+public @interface UiThread {}

firebase-common/firebase-common.gradle

@@ -66,6 +66,7 @@ dependencies {
     implementation project(':firebase-components')
     implementation 'com.google.android.gms:play-services-basement:18.1.0'
     implementation "com.google.android.gms:play-services-tasks:18.0.1"
+    implementation 'androidx.concurrent:concurrent-futures:1.1.0'
 
     // FirebaseApp references storage, so storage needs to be on classpath when dokka runs.
     javadocClasspath project(path: ':firebase-storage')

firebase-common/ktx/ktx.gradle

@@ -38,6 +38,7 @@ android {
 dependencies {
     implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlinVersion"
 
+    implementation project(':firebase-annotations')
     implementation project(':firebase-common')
     implementation project(':firebase-components')
     implementation 'androidx.annotation:annotation:1.1.0'

firebase-common/ktx/src/main/kotlin/com/google/firebase/ktx/Firebase.kt

@@ -17,9 +17,18 @@ import android.content.Context
 import androidx.annotation.Keep
 import com.google.firebase.FirebaseApp
 import com.google.firebase.FirebaseOptions
+import com.google.firebase.annotations.concurrent.Background
+import com.google.firebase.annotations.concurrent.Blocking
+import com.google.firebase.annotations.concurrent.Lightweight
+import com.google.firebase.annotations.concurrent.UiThread
 import com.google.firebase.components.Component
 import com.google.firebase.components.ComponentRegistrar
+import com.google.firebase.components.Dependency
+import com.google.firebase.components.Qualified
 import com.google.firebase.platforminfo.LibraryVersionComponent
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.asCoroutineDispatcher
+import java.util.concurrent.Executor
 
 /**
  * Single access point to all firebase SDKs from Kotlin.
@@ -40,11 +49,11 @@ fun Firebase.initialize(context: Context): FirebaseApp? = FirebaseApp.initialize
 
 /** Initializes and returns a FirebaseApp. */
 fun Firebase.initialize(context: Context, options: FirebaseOptions): FirebaseApp =
-        FirebaseApp.initializeApp(context, options)
+    FirebaseApp.initializeApp(context, options)
 
 /** Initializes and returns a FirebaseApp. */
 fun Firebase.initialize(context: Context, options: FirebaseOptions, name: String): FirebaseApp =
-        FirebaseApp.initializeApp(context, options, name)
+    FirebaseApp.initializeApp(context, options, name)
 
 /** Returns options of default FirebaseApp */
 val Firebase.options: FirebaseOptions
@@ -57,6 +66,27 @@ internal const val LIBRARY_NAME: String = "fire-core-ktx"
 class FirebaseCommonKtxRegistrar : ComponentRegistrar {
     override fun getComponents(): List<Component<*>> {
         return listOf(
-                LibraryVersionComponent.create(LIBRARY_NAME, BuildConfig.VERSION_NAME))
+            LibraryVersionComponent.create(LIBRARY_NAME, BuildConfig.VERSION_NAME),
+            coroutineDispatcher<Background>(),
+            coroutineDispatcher<Lightweight>(),
+            coroutineDispatcher<Blocking>(),
+            coroutineDispatcher<UiThread>()
+        )
     }
 }
+
+private inline fun <reified T : Annotation> coroutineDispatcher(): Component<CoroutineDispatcher> =
+    Component.builder(
+        Qualified.qualified(T::class.java, CoroutineDispatcher::class.java)
+    ).add(
+        Dependency.required(
+            Qualified.qualified(
+                T::class.java,
+                Executor::class.java
+            )
+        )
+    ).factory { c ->
+        c.get(
+            Qualified.qualified(T::class.java, Executor::class.java)
+        ).asCoroutineDispatcher()
+    }.build()

firebase-common/src/main/java/com/google/firebase/FirebaseApp.java

@@ -23,8 +23,6 @@
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.os.Build;
-import android.os.Handler;
-import android.os.Looper;
 import android.text.TextUtils;
 import android.util.Log;
 import androidx.annotation.GuardedBy;
@@ -47,6 +45,7 @@
 import com.google.firebase.components.ComponentRegistrar;
 import com.google.firebase.components.ComponentRuntime;
 import com.google.firebase.components.Lazy;
+import com.google.firebase.concurrent.ExecutorsRegistrar;
 import com.google.firebase.events.Publisher;
 import com.google.firebase.heartbeatinfo.DefaultHeartBeatController;
 import com.google.firebase.inject.Provider;
@@ -59,7 +58,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.CopyOnWriteArrayList;
-import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
 
@@ -97,16 +95,10 @@ public class FirebaseApp {
 
   private static final Object LOCK = new Object();
 
-  private static final Executor UI_EXECUTOR = new UiExecutor();
-
   /** A map of (name, FirebaseApp) instances. */
   @GuardedBy("LOCK")
   static final Map<String, FirebaseApp> INSTANCES = new ArrayMap<>();
 
-  private static final String FIREBASE_ANDROID = "fire-android";
-  private static final String FIREBASE_COMMON = "fire-core";
-  private static final String KOTLIN = "kotlin";
-
   private final Context applicationContext;
   private final String name;
   private final FirebaseOptions options;
@@ -427,9 +419,10 @@ protected FirebaseApp(Context applicationContext, String name, FirebaseOptions o
 
     FirebaseTrace.pushTrace("Runtime");
     componentRuntime =
-        ComponentRuntime.builder(UI_EXECUTOR)
+        ComponentRuntime.builder(com.google.firebase.concurrent.UiExecutor.INSTANCE)
             .addLazyComponentRegistrars(registrars)
             .addComponentRegistrar(new FirebaseCommonRegistrar())
+            .addComponentRegistrar(new ExecutorsRegistrar())
             .addComponent(Component.of(applicationContext, Context.class))
             .addComponent(Component.of(this, FirebaseApp.class))
             .addComponent(Component.of(options, FirebaseOptions.class))
@@ -712,14 +705,4 @@ public void onBackgroundStateChanged(boolean background) {
       }
     }
   }
-
-  private static class UiExecutor implements Executor {
-
-    private static final Handler HANDLER = new Handler(Looper.getMainLooper());
-
-    @Override
-    public void execute(@NonNull Runnable command) {
-      HANDLER.post(command);
-    }
-  }
 }

firebase-common/src/main/java/com/google/firebase/concurrent/CustomThreadFactory.java

@@ -0,0 +1,27 @@
+package com.google.firebase.concurrent;
+
+import java.util.Locale;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.atomic.AtomicLong;
+
+class CustomThreadFactory implements ThreadFactory {
+  private static final ThreadFactory DEFAULT = Executors.defaultThreadFactory();
+  private final AtomicLong threadCount = new AtomicLong();
+  private final String namePrefix;
+  private final int priority;
+
+  CustomThreadFactory(String namePrefix, int priority) {
+    this.namePrefix = namePrefix;
+    this.priority = priority;
+  }
+
+  @Override
+  public Thread newThread(Runnable r) {
+    Thread thread = DEFAULT.newThread(r);
+    thread.setPriority(priority);
+    thread.setName(
+        String.format(Locale.ROOT, "%s Thread #%d", namePrefix, threadCount.getAndIncrement()));
+    return thread;
+  }
+}