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.\"
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.\" Copyright 1998 by the Massachusetts Institute of Technology.
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.\" SPDX-License-Identifier: MIT
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.\"
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.TH ARES_PROCESS 3 "25 July 1998"
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.SH NAME
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ares_process \- Process events for name resolution
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.SH SYNOPSIS
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.nf
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#include <ares.h>
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`ares_channel` -> `ares_channel_t *`: don't bury the pointer (#595)
`ares_channel` is defined as `typedef struct ares_channeldata *ares_channel;`. The problem with this, is it embeds the pointer into the typedef, which means an `ares_channel` can never be declared as `const` as if you write `const ares_channel channel`, that expands to `struct ares_channeldata * const ares_channel` and not `const struct ares_channeldata *channel`.
We will now typedef `ares_channel_t` as `typedef struct ares_channeldata ares_channel_t;`, so if you write `const ares_channel_t *channel`, it properly expands to `const struct ares_channeldata *channel`.
We are maintaining the old typedef for API compatibility with existing integrations, and due to typedef expansion this should not even cause any compiler warnings for existing code. There are no ABI implications with this change. I could be convinced to keep existing public functions as `ares_channel` if a sufficient argument exists, but internally we really need make this change for modern best practices.
This change will allow us to internally use `const ares_channel_t *` where appropriate. Whether or not we decide to change any public interfaces to use `const` may require further discussion on if there might be ABI implications (I don't think so, but I'm also not 100% sure what a compiler internally does with `const` when emitting machine code ... I think more likely ABI implications would occur going the opposite direction).
FYI, This PR was done via a combination of sed and clang-format, the only manual code change was the addition of the new typedef, and a couple doc fixes :)
Fix By: Brad House (@bradh352)
1 year ago
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void ares_process(ares_channel_t *\fIchannel\fP,
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fd_set *\fIread_fds\fP,
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fd_set *\fIwrite_fds\fP)
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`ares_channel` -> `ares_channel_t *`: don't bury the pointer (#595)
`ares_channel` is defined as `typedef struct ares_channeldata *ares_channel;`. The problem with this, is it embeds the pointer into the typedef, which means an `ares_channel` can never be declared as `const` as if you write `const ares_channel channel`, that expands to `struct ares_channeldata * const ares_channel` and not `const struct ares_channeldata *channel`.
We will now typedef `ares_channel_t` as `typedef struct ares_channeldata ares_channel_t;`, so if you write `const ares_channel_t *channel`, it properly expands to `const struct ares_channeldata *channel`.
We are maintaining the old typedef for API compatibility with existing integrations, and due to typedef expansion this should not even cause any compiler warnings for existing code. There are no ABI implications with this change. I could be convinced to keep existing public functions as `ares_channel` if a sufficient argument exists, but internally we really need make this change for modern best practices.
This change will allow us to internally use `const ares_channel_t *` where appropriate. Whether or not we decide to change any public interfaces to use `const` may require further discussion on if there might be ABI implications (I don't think so, but I'm also not 100% sure what a compiler internally does with `const` when emitting machine code ... I think more likely ABI implications would occur going the opposite direction).
FYI, This PR was done via a combination of sed and clang-format, the only manual code change was the addition of the new typedef, and a couple doc fixes :)
Fix By: Brad House (@bradh352)
1 year ago
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void ares_process_fd(ares_channel_t *\fIchannel\fP,
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ares_socket_t \fIread_fd\fP,
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ares_socket_t \fIwrite_fd\fP)
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.fi
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.SH DESCRIPTION
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The \fBares_process(3)\fP function handles input/output events and timeouts
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associated with queries pending on the name service channel identified by
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.IR channel .
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The file descriptor sets pointed to by \fIread_fds\fP and \fIwrite_fds\fP
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should have file descriptors set in them according to whether the file
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descriptors specified by \fIares_fds(3)\fP are ready for reading and writing.
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(The easiest way to determine this information is to invoke \fBselect(3)\fP
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with a timeout no greater than the timeout given by \fIares_timeout(3)\fP).
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The \fBares_process(3)\fP function will invoke callbacks for pending queries
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if they complete successfully or fail.
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\fBares_process_fd(3)\fP works the same way but acts and operates only on the
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specific file descriptors (sockets) you pass in to the function. Use
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ARES_SOCKET_BAD for "no action". This function is provided to allow users of
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c-ares to avoid \fIselect(3)\fP in their applications and within c-ares.
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To only process possible timeout conditions without a socket event occurring,
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one may pass NULL as the values for both \fIread_fds\fP and \fIwrite_fds\fP for
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\fBares_process(3)\fP, or ARES_SOCKET_BAD for both \fIread_fd\fP and
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\fIwrite_fd\fP for \fBares_process_fd(3)\fP.
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.SH EXAMPLE
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The following code fragment waits for all pending queries on a channel
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to complete:
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.nf
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int nfds, count;
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fd_set readers, writers;
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struct timeval tv, *tvp;
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while (1) {
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FD_ZERO(&readers);
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FD_ZERO(&writers);
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nfds = ares_fds(channel, &readers, &writers);
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if (nfds == 0)
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break;
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tvp = ares_timeout(channel, NULL, &tv);
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count = select(nfds, &readers, &writers, NULL, tvp);
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ares_process(channel, &readers, &writers);
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}
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.fi
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.SH SEE ALSO
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.BR ares_fds (3),
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.BR ares_timeout (3)
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