CODEWITHSUNDEEP
socketsudpwinsock2
Slack Groverglow
Slack Groverglow

Reputation: 856

UDP socket gives error WSAETIMEDOUT

I have a call to sendto() for a UDP socket. Sometimes(not always) it blocks my application for ~2.5 seconds. When I check the return value of the sendto() call I get SOCKET_ERROR(-1) and WSAGetLastError() returns WSAETIMEDOUT(10060)

Why would a UDP socket timeout? Under what circumstances would sendto() be a blocking call?

Upvotes: 1

Views: 1539

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 595319

Why would a UDP socket timeout?

It can happen if the socket is running in blocking mode (the default mode), and has a send timeout assigned to it.

Under what circumstances would sendto() be a blocking call?

Sockets are created in blocking mode by default. You have to explicitly request non-blocking behavior if you need it.

In blocking mode, a UDP socket can block if the kernel buffer fills up or if WinSock has to wait for a network event before completing the send. This is documented behavior:

sendto() function

When issuing a blocking Winsock call such as sendto, Winsock may need to wait for a network event before the call can complete. Winsock performs an alertable wait in this situation, which can be interrupted by an asynchronous procedure call (APC) scheduled on the same thread. Issuing another blocking Winsock call inside an APC that interrupted an ongoing blocking Winsock call on the same thread will lead to undefined behavior, and must never be attempted by Winsock clients.

...

If no buffer space is available within the transport system to hold the data to be transmitted, sendto will block unless the socket has been placed in a nonblocking mode. On nonblocking, stream oriented sockets, the number of bytes written can be between 1 and the requested length, depending on buffer availability on both the client and server systems. The select, WSAAsyncSelect or WSAEventSelect function can be used to determine when it is possible to send more data.

Upvotes: 3

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