public class Glide implements ComponentCallbacks2 {
  // ……代码省略……

  @GuardedBy("Glide.class")
  private static volatile Glide glide;

  /**
   * Get the singleton.
   *
   * @return the singleton
   */
  @NonNull
  // Double checked locking is safe here.
  @SuppressWarnings("GuardedBy")
  public static Glide get(@NonNull Context context) {
    if (glide == null) {
      GeneratedAppGlideModule annotationGeneratedModule =
          getAnnotationGeneratedGlideModules(context.getApplicationContext());
      synchronized (Glide.class) {
        if (glide == null) {
          checkAndInitializeGlide(context, annotationGeneratedModule);
        }
      }
    }

    return glide;
  }

  @GuardedBy("Glide.class")
  @VisibleForTesting
  static void checkAndInitializeGlide(
      @NonNull Context context, @Nullable GeneratedAppGlideModule generatedAppGlideModule) {
    // In the thread running initGlide(), one or more classes may call Glide.get(context).
    // Without this check, those calls could trigger infinite recursion.
    if (isInitializing) {
      throw new IllegalStateException(
          "Glide has been called recursively, this is probably an internal library error!");
    }
    isInitializing = true;
    try {
      initializeGlide(context, generatedAppGlideModule);
    } finally {
      isInitializing = false;
    }
  }
  
  @VisibleForTesting
  @Deprecated
  public static synchronized void init(Glide glide) {
    if (Glide.glide != null) {
      tearDown();
    }
    Glide.glide = glide;
  }

  @VisibleForTesting
  public static void init(@NonNull Context context, @NonNull GlideBuilder builder) {
    GeneratedAppGlideModule annotationGeneratedModule = getAnnotationGeneratedGlideModules(context);
    synchronized (Glide.class) {
      if (Glide.glide != null) {
        tearDown();
      }
      initializeGlide(context, builder, annotationGeneratedModule);
    }
  }

  @VisibleForTesting
  public static synchronized boolean isInitialized() {
    return glide != null;
  }

  @GuardedBy("Glide.class")
  private static void initializeGlide(
      @NonNull Context context, @Nullable GeneratedAppGlideModule generatedAppGlideModule) {
    initializeGlide(context, new GlideBuilder(), generatedAppGlideModule);
  }

  @GuardedBy("Glide.class")
  @SuppressWarnings("deprecation")
  private static void initializeGlide(
      @NonNull Context context,
      @NonNull GlideBuilder builder,
      @Nullable GeneratedAppGlideModule annotationGeneratedModule) {
    // ……代码省略……
    Glide glide = builder.build(applicationContext, manifestModules, annotationGeneratedModule);
    applicationContext.registerComponentCallbacks(glide);
    Glide.glide = glide;
  }

  @SuppressWarnings("PMD.UnusedFormalParameter")
  Glide(
      @NonNull Context context,
      @NonNull Engine engine,
      @NonNull MemoryCache memoryCache,
      @NonNull BitmapPool bitmapPool,
      @NonNull ArrayPool arrayPool,
      @NonNull RequestManagerRetriever requestManagerRetriever,
      @NonNull ConnectivityMonitorFactory connectivityMonitorFactory,
      int logLevel,
      @NonNull RequestOptionsFactory defaultRequestOptionsFactory,
      @NonNull Map<Class<?>, TransitionOptions<?, ?>> defaultTransitionOptions,
      @NonNull List<RequestListener<Object>> defaultRequestListeners,
      @NonNull List<GlideModule> manifestModules,
      @Nullable AppGlideModule annotationGeneratedModule,
      @NonNull GlideExperiments experiments) {
    // ……代码省略……
  }
  
  // ……代码省略……
}