python/cpython · error · ValueError

the socket must be non-blocking

Error message

the socket must be non-blocking

What it means

Error "the socket must be non-blocking" thrown in python/cpython.

Source

Thrown at Lib/asyncio/base_events.py:952

    async def getaddrinfo(self, host, port, *,
                          family=0, type=0, proto=0, flags=0):
        if self._debug:
            getaddr_func = self._getaddrinfo_debug
        else:
            getaddr_func = socket.getaddrinfo

        return await self.run_in_executor(
            None, getaddr_func, host, port, family, type, proto, flags)

    async def getnameinfo(self, sockaddr, flags=0):
        return await self.run_in_executor(
            None, socket.getnameinfo, sockaddr, flags)

    async def sock_sendfile(self, sock, file, offset=0, count=None,
                            *, fallback=True):
        if self._debug and sock.gettimeout() != 0:
            raise ValueError("the socket must be non-blocking")
        _check_ssl_socket(sock)
        self._check_sendfile_params(sock, file, offset, count)
        try:
            return await self._sock_sendfile_native(sock, file,
                                                    offset, count)
        except exceptions.SendfileNotAvailableError:
            if not fallback:
                raise
        return await self._sock_sendfile_fallback(sock, file,
                                                  offset, count)

    async def _sock_sendfile_native(self, sock, file, offset, count):
        # NB: sendfile syscall is not supported for SSL sockets and
        # non-mmap files even if sendfile is supported by OS
        raise exceptions.SendfileNotAvailableError(
            f"syscall sendfile is not available for socket {sock!r} "
            f"and file {file!r} combination")

View on GitHub (pinned to bc6749cc3b)

Solutions

1. Call sock.setblocking(False) before handing the socket to the event loop.
2. Or create the socket via loop.create_connection()/create_datagram_endpoint() which set non-blocking mode automatically.

When it happens

Trigger: Raised when a blocking-mode socket is registered with the event loop for async I/O.

Common situations: See trigger scenarios.

AI-assisted analysis of python/cpython@bc6749cc3b (2026-08-14). Data as JSON: /api/errors/7cfe2378af0a719a. Report an issue: GitHub.