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How do you make a socket non-blocking?
I am aware of the fcntl() function, but I've heard it's not always reliable.
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By default, TCP sockets are in "blocking" mode. For example, when you call recv() to read from a stream, control isn't returned to your program until at least one byte of data is read from the remote site. This process of waiting for data to appear is referred to as "blocking".
The default mode of socket calls is blocking. A blocking call does not return to your program until the event you requested has been completed.
In blocking socket mode, a system call event halts the execution until an appropriate reply has been received. In non-blocking sockets, it continues to execute even if the system call has been invoked and deals with its reply appropriately later.
From MSDN, the return value of connect(): On a blocking socket, the return value indicates success or failure of the connection attempt. With a nonblocking socket, the connection attempt cannot be completed immediately. In this case, connect will return SOCKET_ERROR , and WSAGetLastError() will return WSAEWOULDBLOCK.
fcntl() has always worked reliably for me. In any case, here is the function I use to enable/disable blocking on a socket:
#include <fcntl.h> /** Returns true on success, or false if there was an error */ bool SetSocketBlockingEnabled(int fd, bool blocking) { if (fd < 0) return false; #ifdef _WIN32 unsigned long mode = blocking ? 0 : 1; return (ioctlsocket(fd, FIONBIO, &mode) == 0) ? true : false; #else int flags = fcntl(fd, F_GETFL, 0); if (flags == -1) return false; flags = blocking ? (flags & ~O_NONBLOCK) : (flags | O_NONBLOCK); return (fcntl(fd, F_SETFL, flags) == 0) ? true : false; #endif } If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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