errno 103 (EALREADY): meaning and diagnosis

Status / error code:		Category:

Constant name:
Source:		Operating System:
Description: A UCRT POSIX-supplement status for a second attempt to start an operation that is already in progress.

Could be also:
Constant	Type	OS
ERROR_TOO_MANY_SEM_REQUESTS	Win32 error	Windows
HTTP_EARLY_HINTS	HTTP Code	Any
ECONNABORTED	errno	Linux
ENOPOLICY	errno	Mac
CONFIG_INITIALIZATION_FAILED	BugCheck Code	Windows

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EAFNOSUPPORT	EBADMSG

EALREADY

EALREADY means the caller attempted to start an operation that has not reached a terminal state from an earlier attempt. It is especially relevant to nonblocking connection establishment, but the core diagnostic question is generic: which operation owns the state transition, and what completion or cancellation rule has not yet been observed?

For a native nonblocking Winsock connection, the corresponding status is normally WSAEALREADY, retrieved with WSAGetLastError(). Do not translate it into “the connection succeeded.” A successful connection, a pending connection, and a failed connection need distinct states and distinct evidence.

State-machine evidence

Record the socket identifier, connection attempt sequence number, destination, and the first call that moved the object into a pending state.
Wait for the documented completion indication, then retrieve the final socket error instead of issuing another connect blindly.
Ensure timeout and cancellation code remove or supersede the pending attempt exactly once.
When pooling sockets, prevent two callers from initiating the same connection on the same object concurrently.

References

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