向SynchronizedMap和synchronized块添加或删除

我正在使用AWS Android SDK将图像文件上传到S3 bucket。我在一个线程中执行裁剪操作,该线程在裁剪完成后开始传输图像文件。我将所有TransferObserver实例保存在映射中,定义和初始化如下:

private Map<String, TransferObserver> transferObservers;

A() {
    transferObservers = Collections.synchronizedMap(new LinkedHashMap<String, TransferObserver>());
}

public void add(Image image) {
    handler.post(new Runnable() {
        @Override
        public void run() {
            // Cropping
            ...
            TransferObserver uploadObserver = transferUtility.upload(key, new File(localFilePath));
            uploadObserver.setTransferListener(new TransferListener() {
            photoTransferObservers.put(image.getPath(), uploadObserver);
        }
    }
}

可以删除图像,以便其在地图中的条目:

public void deleteTransferRecord(String key) {
    transferObservers.remove(key);
}

还有一个函数返回上传的整个过程:

private void notifyListeners() {
    int completedUploadCount = 0;
    for (TransferObserver transferObserver : transferObservers.values()) {
        if (transferObserver.getState() == TransferState.COMPLETED) {
            completedUploadCount++;
        }
    }
    ...
}

transferObservers . 我应该如何更新代码以防止任何并发问题?