Add a precondition check for not main thread

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/common/IdManager.java

@@ -104,7 +104,6 @@ private static String formatId(@NonNull String id) {
   @Override
   @NonNull
   public synchronized InstallIds getInstallIds() {
-    CrashlyticsWorkers.checkBackgroundThread();
     if (!shouldRefresh()) {
       return installIds;
     }
@@ -183,7 +182,7 @@ private String readCachedCrashlyticsInstallId(SharedPreferences prefs) {
    */
   @NonNull
   public FirebaseInstallationId fetchTrueFid(boolean validate) {
-    CrashlyticsWorkers.checkBackgroundThread(); // This fetch blocks, never do it on main.
+    CrashlyticsWorkers.checkNotMainThread(); // This fetch blocks, never do it on main.
     String fid = null;
     String authToken = null;
 

firebase-crashlytics/src/main/java/com/google/firebase/crashlytics/internal/concurrency/CrashlyticsWorkers.kt

@@ -16,6 +16,8 @@
 
 package com.google.firebase.crashlytics.internal.concurrency
 
+import android.os.Build
+import android.os.Looper
 import com.google.firebase.crashlytics.internal.Logger
 import java.util.concurrent.ExecutorService
 
@@ -59,6 +61,12 @@ class CrashlyticsWorkers(
     /** When enabled, failed preconditions will cause assertion errors for debugging. */
     @JvmStatic var enforcement: Boolean = false
 
+    @JvmStatic
+    fun checkNotMainThread() =
+      checkThread(::isNotMainThread) {
+        "Must not be called on a main thread, was called on $threadName."
+      }
+
     @JvmStatic
     fun checkBlockingThread() =
       checkThread(::isBlockingThread) {
@@ -71,6 +79,13 @@ class CrashlyticsWorkers(
         "Must be called on a background thread, was called on $threadName."
       }
 
+    private fun isNotMainThread() =
+      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
+        !Looper.getMainLooper().isCurrentThread
+      } else {
+        Looper.getMainLooper() != Looper.myLooper()
+      }
+
     private fun isBlockingThread() = threadName.contains("Firebase Blocking Thread #")
 
     private fun isBackgroundThread() = threadName.contains("Firebase Background Thread #")