public void restartRequests() {
        for (Request request : Util.getSnapshot(requests)) {
            if (!request.isComplete() && !request.isCancelled()) {
                // Ensure the request will be restarted in onResume.
                request.pause();
                if (!isPaused) {
                    request.begin();
                } else {
                    pendingRequests.add(request);
                }
            }
        }
    }
Restarts failed requests and cancels and restarts in progress requests.
core/src/main/java/com/bumptech/glide/manager/RequestTracker.java