mod_fastcgi.c

static int fcgi_demux_response(server *srv, handler_ctx *hctx) {
/* ... */
    int toread;
/* ... */
    /*
     * check how much we have to read
     */
    if (ioctl(hctx->fd, FIONREAD, &toread)) {
        /* we never get here */
        /* NOTE: hctx->fd is the fd to the fastcgi process */
        /* NOTE: FIONREAD "Get the number of bytes that are immediately available for reading." */
        /* NOTE: toread is where the number of bytes is placed */
    }
/* ... */
    /* init read-buffer */

    if (toread > 0) {
        /* we never get here */
    } else {
        /* this is where the error occurs. toread is not greater than zero */
        log_error_write(srv, __FILE__, __LINE__, "ssdsb",
                "unexpected end-of-file (perhaps the fastcgi process died):",
                "pid:", proc->pid,
                "socket:", proc->connection_name);

        return -1;
    }
    /* rest of the function is irrelevant since it returned already */
}