php-deluxe.net - description Overlapped I O

Overlapped I/O

In Microsoft Windows, Overlapped I/O is a feature of the application programming interfaces for file operations, introduced by Windows NT. For asynchronous I/O reads and writes, one may pass a special OVERLAPPED structure to the ReadFile() and WriteFile() functions, and the operation will be completed later. Optionally, you may specify a Win32 event handle to be raised when the operation completes.

A possible Unix analogue to the overlapped I/O concept would be non-blocking file descriptors. However, these would require significant restructuring of code to get the same result, as the Unix code would have to repeatedly retry the operation. Another possibility would be the POSIX asynchronous I/O API, however it is not universally supported.

Overlapped I/O is particularly useful for sockets and pipes. It is not well supported by Windows 95.

= External links =

[http://msdn.microsoft.com/library/default.aspurl=/library/en-us/fileio/fs/readfile.asp MSDN Reference: ReadFile()]

[http://msdn.microsoft.com/library/default.aspurl=/library/en-us/fileio/fs/writefile.asp MSDN Reference: WriteFile()]

[http://msdn.microsoft.com/library/default.aspurl=/library/en-us/dllproc/base/overlapped_str.asp MSDN Reference: OVERLAPPED Data structure]