Windows error 10038 (WSAENOTSOCK): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: The value supplied where Winsock required a socket is not an active socket descriptor.

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WSAEALREADY	WSAEDESTADDRREQ

WSAENOTSOCK

WSAENOTSOCK means that the argument passed as a socket does not currently identify a Winsock socket. It is usually an application lifecycle or type-handling defect, not a remote networking problem.

Common ways this happens

A socket may have been closed and then reused, a non-socket handle may have been passed through a generic handle abstraction, or concurrent teardown may race with an I/O or readiness call. The failure can also follow incorrect cross-process hand-off: Windows supports socket duplication through WSADuplicateSocket, but simply copying a numeric handle value to another process is not the same thing.

How to investigate

Record creation, duplication, ownership transfer, and close events with the numeric SOCKET value.
Ensure one component owns the transition to closed and that pending I/O observes that state before reusing objects.
Check that socket APIs are not being called on ordinary file, event, or CRT-descriptor values.

Microsoft: accept errors · Microsoft: WSADuplicateSocket · The Open Group: socket descriptors

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