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parameters (like \UNIX) are commonly entered using an empty group to separate the markup from a following inter-word space; this is not needed when the next character is punctuation, or the markup is the last thing in the enclosing group. These cases were marked inconsistently; the empty group is now *only* used when needed.
175 lines
6 KiB
TeX
175 lines
6 KiB
TeX
% Manual text and implementation by Jaap Vermeulen
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\section{\module{posixfile} ---
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File-like objects with locking support}
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\declaremodule{builtin}{posixfile}
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\platform{Unix}
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\modulesynopsis{A file-like object with support for locking.}
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\moduleauthor{Jaap Vermeulen}{}
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\sectionauthor{Jaap Vermeulen}{}
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\indexii{\POSIX}{file object}
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\deprecated{1.5}{The locking operation that this module provides is
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done better and more portably by the
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\function{\refmodule{fcntl}.lockf()} call.
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\withsubitem{(in module fcntl)}{\ttindex{lockf()}}}
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This module implements some additional functionality over the built-in
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file objects. In particular, it implements file locking, control over
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the file flags, and an easy interface to duplicate the file object.
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The module defines a new file object, the posixfile object. It
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has all the standard file object methods and adds the methods
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described below. This module only works for certain flavors of
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\UNIX, since it uses \function{fcntl.fcntl()} for file locking.%
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\withsubitem{(in module fcntl)}{\ttindex{fcntl()}}
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To instantiate a posixfile object, use the \function{open()} function
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in the \module{posixfile} module. The resulting object looks and
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feels roughly the same as a standard file object.
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The \module{posixfile} module defines the following constants:
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\begin{datadesc}{SEEK_SET}
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Offset is calculated from the start of the file.
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\end{datadesc}
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\begin{datadesc}{SEEK_CUR}
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Offset is calculated from the current position in the file.
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\end{datadesc}
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\begin{datadesc}{SEEK_END}
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Offset is calculated from the end of the file.
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\end{datadesc}
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The \module{posixfile} module defines the following functions:
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\begin{funcdesc}{open}{filename\optional{, mode\optional{, bufsize}}}
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Create a new posixfile object with the given filename and mode. The
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\var{filename}, \var{mode} and \var{bufsize} arguments are
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interpreted the same way as by the built-in \function{open()}
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function.
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\end{funcdesc}
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\begin{funcdesc}{fileopen}{fileobject}
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Create a new posixfile object with the given standard file object.
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The resulting object has the same filename and mode as the original
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file object.
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\end{funcdesc}
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The posixfile object defines the following additional methods:
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\setindexsubitem{(posixfile method)}
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\begin{funcdesc}{lock}{fmt, \optional{len\optional{, start\optional{, whence}}}}
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Lock the specified section of the file that the file object is
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referring to. The format is explained
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below in a table. The \var{len} argument specifies the length of the
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section that should be locked. The default is \code{0}. \var{start}
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specifies the starting offset of the section, where the default is
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\code{0}. The \var{whence} argument specifies where the offset is
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relative to. It accepts one of the constants \constant{SEEK_SET},
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\constant{SEEK_CUR} or \constant{SEEK_END}. The default is
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\constant{SEEK_SET}. For more information about the arguments refer
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to the \manpage{fcntl}{2} manual page on your system.
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\end{funcdesc}
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\begin{funcdesc}{flags}{\optional{flags}}
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Set the specified flags for the file that the file object is referring
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to. The new flags are ORed with the old flags, unless specified
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otherwise. The format is explained below in a table. Without
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the \var{flags} argument
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a string indicating the current flags is returned (this is
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the same as the \samp{?} modifier). For more information about the
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flags refer to the \manpage{fcntl}{2} manual page on your system.
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\end{funcdesc}
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\begin{funcdesc}{dup}{}
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Duplicate the file object and the underlying file pointer and file
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descriptor. The resulting object behaves as if it were newly
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opened.
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\end{funcdesc}
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\begin{funcdesc}{dup2}{fd}
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Duplicate the file object and the underlying file pointer and file
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descriptor. The new object will have the given file descriptor.
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Otherwise the resulting object behaves as if it were newly opened.
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\end{funcdesc}
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\begin{funcdesc}{file}{}
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Return the standard file object that the posixfile object is based
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on. This is sometimes necessary for functions that insist on a
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standard file object.
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\end{funcdesc}
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All methods raise \exception{IOError} when the request fails.
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Format characters for the \method{lock()} method have the following
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meaning:
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\begin{tableii}{c|l}{samp}{Format}{Meaning}
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\lineii{u}{unlock the specified region}
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\lineii{r}{request a read lock for the specified section}
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\lineii{w}{request a write lock for the specified section}
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\end{tableii}
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In addition the following modifiers can be added to the format:
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\begin{tableiii}{c|l|c}{samp}{Modifier}{Meaning}{Notes}
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\lineiii{|}{wait until the lock has been granted}{}
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\lineiii{?}{return the first lock conflicting with the requested lock, or
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\code{None} if there is no conflict.}{(1)}
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\end{tableiii}
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\noindent
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Note:
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\begin{description}
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\item[(1)] The lock returned is in the format \code{(\var{mode}, \var{len},
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\var{start}, \var{whence}, \var{pid})} where \var{mode} is a character
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representing the type of lock ('r' or 'w'). This modifier prevents a
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request from being granted; it is for query purposes only.
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\end{description}
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Format characters for the \method{flags()} method have the following
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meanings:
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\begin{tableii}{c|l}{samp}{Format}{Meaning}
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\lineii{a}{append only flag}
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\lineii{c}{close on exec flag}
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\lineii{n}{no delay flag (also called non-blocking flag)}
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\lineii{s}{synchronization flag}
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\end{tableii}
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In addition the following modifiers can be added to the format:
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\begin{tableiii}{c|l|c}{samp}{Modifier}{Meaning}{Notes}
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\lineiii{!}{turn the specified flags 'off', instead of the default 'on'}{(1)}
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\lineiii{=}{replace the flags, instead of the default 'OR' operation}{(1)}
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\lineiii{?}{return a string in which the characters represent the flags that
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are set.}{(2)}
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\end{tableiii}
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\noindent
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Notes:
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\begin{description}
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\item[(1)] The \samp{!} and \samp{=} modifiers are mutually exclusive.
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\item[(2)] This string represents the flags after they may have been altered
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by the same call.
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\end{description}
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Examples:
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\begin{verbatim}
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import posixfile
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file = posixfile.open('/tmp/test', 'w')
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file.lock('w|')
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...
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file.lock('u')
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file.close()
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\end{verbatim}
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