Android设备如何保证数据同步写入磁盘的实现

时间:2021-05-20

在一些特定的工作场景中,我们把数据及时写出磁盘,而不是暂时保存在系统的文件缓存区,防止掉电导致数据丢失

/** * Force all system buffers to synchronize with the underlying * device. This method returns after all modified data and * attributes of this FileDescriptor have been written to the * relevant device(s). In particular, if this FileDescriptor * refers to a physical storage medium, such as a file in a file * system, sync will not return until all in-memory modified copies * of buffers associated with this FileDescriptor have been * written to the physical medium. * * sync is meant to be used by code that requires physical * storage (such as a file) to be in a known state For * example, a class that provided a simple transaction facility * might use sync to ensure that all changes to a file caused * by a given transaction were recorded on a storage medium. * * sync only affects buffers downstream of this FileDescriptor. If * any in-memory buffering is being done by the application (for * example, by a BufferedOutputStream object), those buffers must * be flushed into the FileDescriptor (for example, by invoking * OutputStream.flush) before that data will be affected by sync. * * @exception SyncFailedException * Thrown when the buffers cannot be flushed, * or because the system cannot guarantee that all the * buffers have been synchronized with physical media. * @since JDK1.1 */public native void sync() throws SyncFailedException;

可能一看到这个场景,很多人会想到数据库的事务,查看Android数据库sqlite的源码可以看到,数据库事务只能保证n个操作,要么都执行,要么都不执行。数据库事务在所有操作完成后,会提醒文件系统与磁盘同步,但是不会等到所有系统缓冲区与磁盘同步完成才返回!

FileDescriptor.getFd().sync();会强制所有系统缓冲区与磁盘同步File file = new File("/sdcard/a.txt"); try { FileOutputStream outputStream = new FileOutputStream(file); outputStream.write("kuangxf".getBytes()); outputStream.flush(); //强制文件系统刷新 outputStream.getFD().sync(); } catch (Exception e) { e.printStackTrace(); }

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持。

声明:本页内容来源网络,仅供用户参考;我单位不保证亦不表示资料全面及准确无误,也不保证亦不表示这些资料为最新信息,如因任何原因,本网内容或者用户因倚赖本网内容造成任何损失或损害,我单位将不会负任何法律责任。如涉及版权问题,请提交至online#300.cn邮箱联系删除。

相关文章