Add a precondition check for not main thread (#6204)

Add a precondition check for not main thread. This is more useful when
we just want to enforce not main thread, not a specific 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 #")