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Man Pages
ARES_PROCESS(3) FreeBSD 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

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