ARES_PROCESS(3) Library Functions Manual ARES_PROCESS(3)

ares_process - Process events for name resolution

#include <ares.h>
void ares_process(ares_channel channel,

fd_set *read_fds,
fd_set *write_fds) void ares_process_fd(ares_channel channel,
ares_socket_t read_fd,
ares_socket_t write_fd)

The ares_process(3) function handles input/output events and timeouts associated with queries pending on the name service channel identified by channel. The file descriptor sets pointed to by read_fds and write_fds should have file descriptors set in them according to whether the file descriptors specified by ares_fds(3) are ready for reading and writing. (The easiest way to determine this information is to invoke select(3) with a timeout no greater than the timeout given by ares_timeout(3)).

The ares_process(3) function will invoke callbacks for pending queries if they complete successfully or fail.

ares_process_fd(3) works the same way but acts and operates only on the specific file descriptors (sockets) you pass in to the function. Use ARES_SOCKET_BAD for "no action". This function is provided to allow users of c-ares to void select(3) in their applications and within c-ares.

To only process possible timeout conditions without a socket event occurring, one may pass NULL as the values for both read_fds and write_fds for ares_process(3), or ARES_SOCKET_BAD for both read_fd and write_fd for ares_process_fd(3).

The following code fragment waits for all pending queries on a channel to complete:

int nfds, count;
fd_set readers, writers;
struct timeval tv, *tvp;
while (1) {

FD_ZERO(&readers);
FD_ZERO(&writers);
nfds = ares_fds(channel, &readers, &writers);
if (nfds == 0)
break;
tvp = ares_timeout(channel, NULL, &tv);
count = select(nfds, &readers, &writers, NULL, tvp);
ares_process(channel, &readers, &writers); }

ares_fds(3), ares_timeout(3)

Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.

25 July 1998