Increasing limit of FD_SETSIZE and select

c, file-descriptor, linux

Solution

Per the standards, there is no way to increase `FD_SETSIZE`. Some programs and libraries (libevent comes to mind) try to work around this by allocating additional space for the `fd_set` object and passing values larger than `FD_SETSIZE` to the `FD_*` macros, but this is a very bad idea since robust implementations may perform bounds-checking on the argument and abort if it's out of range.

I have an alternate solution that should always work (even though it's not required to by the standards). Instead of a single `fd_set` object, allocate an array of them large enough to hold the max fd you'll need, then use `FD_SET(fd%FD_SETSIZE, &fds_array[fd/FD_SETSIZE])` etc. to access the set.

Problem

Original source