ares_process - Process events for name resolution


#include <ares.h>
void ares_process(ares_channel_t *channel,
                  fd_set *read_fds,
                  fd_set *write_fds)
void ares_process_fd(ares_channel_t *channel,
                     ares_socket_t read_fd,
                     ares_socket_t write_fd)


The ares_process 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 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).

The ares_process 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 avoid 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, 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) {
  nfds = ares_fds(channel, &readers, &writers);
  if (nfds == 0)
  tvp = ares_timeout(channel, NULL, &tv);
  count = select(nfds, &readers, &writers, NULL, tvp);
  ares_process(channel, &readers, &writers);

See also

ares_fds(3), ares_timeout(3)

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