51 lines
1.6 KiB
Plaintext
51 lines
1.6 KiB
Plaintext
@node select
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@subsection @code{select}
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@findex select
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POSIX specification:@* @url{https://pubs.opengroup.org/onlinepubs/9799919799/functions/select.html}
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Gnulib module: select
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@mindex select
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Portability problems fixed by Gnulib:
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@itemize
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@item
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This function is declared in @code{<winsock2.h>}
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instead of @code{<sys/select.h>}
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on some platforms:
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mingw, MSVC 14.
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@item
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On Windows platforms (excluding Cygwin), @code{select} can only be
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called on descriptors created by the @code{socket} function, not on regular
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file descriptors.
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@item
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On Windows platforms (excluding Cygwin), error codes from this function
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are not placed in @code{errno}, and @code{WSAGetLastError} must be used
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instead.
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@item
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On some platforms, this function fails to detect invalid fds with
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EBADF, but only if they lie beyond the current maximum open fd:
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FreeBSD 8.2.
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@end itemize
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Portability problems not fixed by Gnulib:
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@itemize
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@item
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When you call @code{select} with a timeout, some implementations modify the
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timeout parameter so that upon return from the function, it contains the
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amount of time not slept. Other implementations leave the timeout parameter
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unmodified.
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@item
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Under Windows, when passing a pipe, Gnulib's @code{select} replacement might
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return 0 even before the timeout has passed. Programs using it with pipes can
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thus busy wait.
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@item
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On Linux, when some file descriptor refers to a regular file, @code{select}
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may fail, setting @code{errno} to @code{EBADF}.
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@item
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On Haiku,
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@c https://dev.haiku-os.org/ticket/19220
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the maximum allowed value for the first argument is not @code{FD_SETSIZE}
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but @code{FD_SETSIZE / 2}.
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@end itemize
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