100 lines
3.2 KiB
TeX
100 lines
3.2 KiB
TeX
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\section{\module{dl} ---
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Call C functions in shared objects}
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\declaremodule{extension}{dl}
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\platform{Unix} %?????????? Anyone????????????
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\sectionauthor{Moshe Zadka}{mzadka@geocities.com}
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\modulesynopsis{Call C functions in shared objects.}
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The \module{dl} module defines an interface to the
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\cfunction{dlopen()} function, which is the most common interface on
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\UNIX{} platforms for handling dynamically linked libraries. It allows
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the program to call arbitary functions in such a library.
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\strong{Note:} This module will not work unless
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\begin{verbatim}
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sizeof(int) == sizeof(long) == sizeof(char *)
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\end{verbatim}
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If this is not the case, \exception{SystemError} will be raised on
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import.
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The \module{dl} module defines the following function:
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\begin{funcdesc}{open}{name\optional{, mode\code{ = RTLD_LAZY}}}
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Open a shared object file, and return a handle. Mode
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signifies late binding (\constant{RTLD_LAZY}) or immediate binding
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(\constant{RTLD_NOW}). Default is \constant{RTLD_LAZY}. Note that some
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sytems do not support \constant{RTLD_NOW}.
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Return value is a \pytype{dlobject}.
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\end{funcdesc}
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The \module{dl} module defines the following constants:
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\begin{datadesc}{RTLD_LAZY}
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Useful as an argument to \function{open()}.
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\end{datadesc}
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\begin{datadesc}{RTLD_NOW}
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Useful as an argument to \function{open()}. Note that on systems
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which do not support immediate binding, this constant will not appear
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in the module. For maximum portability, use \function{hasattr()} to
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determine if the system supports immediate binding.
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\end{datadesc}
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The \module{dl} module defines the following exception:
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\begin{excdesc}{error}
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Exception raised when an error has occured inside the dynamic loading
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and linking routines.
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\end{excdesc}
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Example:
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\begin{verbatim}
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>>> import dl, time
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>>> a=dl.open('/lib/libc.so.6')
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>>> a.call('time'), time.time()
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(929723914, 929723914.498)
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\end{verbatim}
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This example was tried on a Debian GNU/Linux system, and is a good
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example of the fact that using this module is usually a bad alternative.
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\subsection{Dl Objects \label{dl-objects}}
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Dl objects, as returned by \function{open()} above, have the
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following methods:
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\begin{methoddesc}{close}{}
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Free all resources, except the memory.
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\end{methoddesc}
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\begin{methoddesc}{sym}{name}
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Return the pointer for the function named \var{name}, as a number, if
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it exists in the referenced shared object, otherwise \code{None}. This
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is useful in code like:
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\begin{verbatim}
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>>> if a.sym('time'):
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... a.call('time')
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... else:
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... time.time()
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\end{verbatim}
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(Note that this function will return a non-zero number, as zero is the
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\NULL{} pointer)
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\end{methoddesc}
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\begin{methoddesc}{call}{name\optional{, arg1\optional{, arg2\ldots}}}
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Call the function named \var{name} in the referenced shared object.
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The arguments must be either Python integers, which will be
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passed as is, Python strings, to which a pointer will be passed,
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or \code{None}, which will be passed as \NULL{}. Note that
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strings should only be passed to functions as \ctype{const char*}, as
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Python will not like its string mutated.
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There must be at most 10 arguments, and arguments not given will be
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treated as \code{None}. The function's return value must be a C
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\ctype{long}, which is a Python integer.
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\end{methoddesc}
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