第二种模式更有效，它使用较少的内存，并省去了创建和删除临时文件的烦恼。
The second model is more efficient, it USES less memory, and saves you from the headache of creating and deleting temporary files.
该表单知道查找那个临时文件，读取它，如果必要的话填充它，然后删除它。
The form knows to look for that temporary file, reads it, populates it as necessary, and deletes the file.
此代码小心地断开与临时文件的链接(让它仍是打开的，但已经被删除)来进行自动清空。
This code carefully unlinks the temporary file, leaving it open but already removed, to clean up automatically.
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