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Another more important problem is that each thread can only make one send call at a time, which is extremely inefficient. For example, the other party may have insufficient resources, causing AFD.SYS to fail to copy the data to the application. The problem is that even if the remote TCP informs that the data has been received, it does not actually mean that the data has been successfully sent to the client application. It seems that this is a simple way to determine whether your data has been received by the other party, but in fact it is not the case, which is very bad. In this case, the system kernel will lock the application buffer until the receiver confirms that the send() call returns. However, doing so will bring some consequences:įor example, an application program sets SO_SNDBUF to 0, closes the buffer (referring to the buffer in AFD.SYS), and then issues a synchronous block send() call. Developers can use the setsockopt API function to change the values of SO_SNDBUF and SO_RCVBUF to 0 to turn off the internal buffer of AFD.SYS. Especially when the application uses the general send and receive routines that do not involve the use of Overlapped. When the application program calls recv or WSARecv function, the data is copied from the buffer of AFD.SYS to the buffer provided by the application program. Similarly, when receiving data from a remote client, if the application does not submit a receive request, and the online data does not exceed the buffer size set by SO_RCVBUF, then AFD.SYS copies the data on the network to its internal buffer for storage.
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Of course, if the application wants to send data larger than the buffer set by SO_SNDBUF, the WSASend function will be blocked until all data has been sent. After the data is sent to the network by AFD.SYS, it has nothing to do with the application. In other words, when a program calls the send or WSASend function to send data, the data is copied to the internal buffer of AFD.SYS (the size is set according to SO_SNDBUF), and then send and WSASend return immediately.
#Windows afd socket buffer size missing driver
AFD.SYS communicates data through TDI and the transmission protocol driver layer.ġ: Who is responsible for managing the buffer zone?Īs mentioned above, AFD.SYS is responsible for buffer management for applications that use the socket interface to communicate with the transport protocol layer. This driver is responsible for connection and buffer management, and provides a socket-style programming interface to the application. Then, the socket method (implemented in AFD.SYS) is provided through the Winsock kernel mode driver. These APIs separate WinNT subsystems from various network programming interfaces. Instead, more general APIs are implemented, called Transport Driver Interface (TDI).
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#Windows afd socket buffer size missing windows
For the development of large-scale responsive Winsock applications, a basic understanding of the socket architecture of Windows NT and Windows 2000 is very helpful.ĭifferent from other operating systems, the transport protocol layer of WinNT and Win2000 does not directly provide socket-style interfaces to applications and does not accept direct access from applications.