WSAEALREADY - 10037 (0x2735)
An operation was attempted on a non-blocking socket that already had an operation in progress.
Updated: Feb 21, 2026
Technical Meaning
The WSAEALREADY error code indicates that an operation was attempted on a non-blocking socket, but the socket already had another operation in progress. This typically occurs when attempting to perform an operation that would block (such as sending or receiving data) while there is still an ongoing asynchronous operation on the same socket.
Error Details
- Error Name: WSAEALREADY
- Numeric Code: 10037
- Hex Code: 0x2735
This error suggests that the application attempted to initiate a new operation on a non-blocking socket before the previous asynchronous operation had completed. Non-blocking sockets are designed to allow applications to continue executing while waiting for I/O operations, but they must handle the possibility of multiple concurrent operations.
Usage Context
Non-blocking sockets are commonly used in network programming where applications need to perform other tasks while waiting for data to be received or transmitted. The WSAEALREADY error can occur when an application attempts to start a new operation without properly checking if there is already an ongoing operation on the socket.
Developer Interpretation
Developers should ensure that they correctly manage asynchronous operations on non-blocking sockets to avoid this error. This includes checking the return values of previous I/O operations and handling them appropriately before attempting new operations. Proper synchronization mechanisms, such as event handlers or completion ports, are essential for managing multiple concurrent operations.
Related Errors
- WSAEWOULDBLOCK: Operation would block (occurs when a blocking operation is attempted on a non-blocking socket).
- WSAEINPROGRESS: An I/O operation is already in progress (similar to WSAEALREADY but more general).
FAQ
Q: What does the WSAEALREADY error mean?
A: It indicates that an attempt was made to start a new operation on a non-blocking socket while another operation was still in progress.
Q: How can I avoid this error?
A: Ensure that you check for ongoing operations before attempting new ones and handle the return values appropriately.
Summary
The WSAEALREADY error is specific to non-blocking sockets and indicates an attempt to initiate a new operation while another operation was already in progress. Developers should manage asynchronous operations carefully to avoid this error, ensuring proper synchronization and handling of I/O events.