Windows error 10035 (WSAEWOULDBLOCK): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A non-blocking socket operation could not be completed immediately.

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WSAEMFILE	WSAEINPROGRESS

WSAEWOULDBLOCK

WSAEWOULDBLOCK means that a Winsock operation on a nonblocking socket cannot make progress immediately. It is normally a state notification, not proof that the connection or socket is broken.

Typical situations

It is commonly returned by connect while a nonblocking connection is still being established, by recv when no input is queued, and by accept when no client is waiting. The operation must not be retried in a tight loop.

What to do

For a pending connect, wait for the completion notification registered for the socket, such as select, WSAEventSelect, or WSAAsyncSelect.
For receive or accept, wait until the readiness mechanism reports data or a queued connection.
Keep the operation state in the application; a nonblocking call may need to be continued later.

Microsoft: connect · Microsoft: recv

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