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-% Manual text and implementation by Jaap Vermeulen
-\section{\module{posixfile} ---
- File-like objects with locking support}
-
-\declaremodule{builtin}{posixfile}
- \platform{Unix}
-\modulesynopsis{A file-like object with support for locking.}
-\moduleauthor{Jaap Vermeulen}{}
-\sectionauthor{Jaap Vermeulen}{}
-
-
-\indexii{\POSIX}{file object}
-
-\deprecated{1.5}{The locking operation that this module provides is
-done better and more portably by the
-\function{\refmodule{fcntl}.lockf()} call.
-\withsubitem{(in module fcntl)}{\ttindex{lockf()}}}
-
-This module implements some additional functionality over the built-in
-file objects. In particular, it implements file locking, control over
-the file flags, and an easy interface to duplicate the file object.
-The module defines a new file object, the posixfile object. It
-has all the standard file object methods and adds the methods
-described below. This module only works for certain flavors of
-\UNIX, since it uses \function{fcntl.fcntl()} for file locking.%
-\withsubitem{(in module fcntl)}{\ttindex{fcntl()}}
-
-To instantiate a posixfile object, use the \function{open()} function
-in the \module{posixfile} module. The resulting object looks and
-feels roughly the same as a standard file object.
-
-The \module{posixfile} module defines the following constants:
-
-
-\begin{datadesc}{SEEK_SET}
-Offset is calculated from the start of the file.
-\end{datadesc}
-
-\begin{datadesc}{SEEK_CUR}
-Offset is calculated from the current position in the file.
-\end{datadesc}
-
-\begin{datadesc}{SEEK_END}
-Offset is calculated from the end of the file.
-\end{datadesc}
-
-The \module{posixfile} module defines the following functions:
-
-
-\begin{funcdesc}{open}{filename\optional{, mode\optional{, bufsize}}}
- Create a new posixfile object with the given filename and mode. The
- \var{filename}, \var{mode} and \var{bufsize} arguments are
- interpreted the same way as by the built-in \function{open()}
- function.
-\end{funcdesc}
-
-\begin{funcdesc}{fileopen}{fileobject}
- Create a new posixfile object with the given standard file object.
- The resulting object has the same filename and mode as the original
- file object.
-\end{funcdesc}
-
-The posixfile object defines the following additional methods:
-
-\begin{methoddesc}[posixfile]{lock}{fmt, \optional{len\optional{, start\optional{, whence}}}}
- Lock the specified section of the file that the file object is
- referring to. The format is explained
- below in a table. The \var{len} argument specifies the length of the
- section that should be locked. The default is \code{0}. \var{start}
- specifies the starting offset of the section, where the default is
- \code{0}. The \var{whence} argument specifies where the offset is
- relative to. It accepts one of the constants \constant{SEEK_SET},
- \constant{SEEK_CUR} or \constant{SEEK_END}. The default is
- \constant{SEEK_SET}. For more information about the arguments refer
- to the \manpage{fcntl}{2} manual page on your system.
-\end{methoddesc}
-
-\begin{methoddesc}[posixfile]{flags}{\optional{flags}}
- Set the specified flags for the file that the file object is referring
- to. The new flags are ORed with the old flags, unless specified
- otherwise. The format is explained below in a table. Without
- the \var{flags} argument
- a string indicating the current flags is returned (this is
- the same as the \samp{?} modifier). For more information about the
- flags refer to the \manpage{fcntl}{2} manual page on your system.
-\end{methoddesc}
-
-\begin{methoddesc}[posixfile]{dup}{}
- Duplicate the file object and the underlying file pointer and file
- descriptor. The resulting object behaves as if it were newly
- opened.
-\end{methoddesc}
-
-\begin{methoddesc}[posixfile]{dup2}{fd}
- Duplicate the file object and the underlying file pointer and file
- descriptor. The new object will have the given file descriptor.
- Otherwise the resulting object behaves as if it were newly opened.
-\end{methoddesc}
-
-\begin{methoddesc}[posixfile]{file}{}
- Return the standard file object that the posixfile object is based
- on. This is sometimes necessary for functions that insist on a
- standard file object.
-\end{methoddesc}
-
-All methods raise \exception{IOError} when the request fails.
-
-Format characters for the \method{lock()} method have the following
-meaning:
-
-\begin{tableii}{c|l}{samp}{Format}{Meaning}
- \lineii{u}{unlock the specified region}
- \lineii{r}{request a read lock for the specified section}
- \lineii{w}{request a write lock for the specified section}
-\end{tableii}
-
-In addition the following modifiers can be added to the format:
-
-\begin{tableiii}{c|l|c}{samp}{Modifier}{Meaning}{Notes}
- \lineiii{|}{wait until the lock has been granted}{}
- \lineiii{?}{return the first lock conflicting with the requested lock, or
- \code{None} if there is no conflict.}{(1)}
-\end{tableiii}
-
-\noindent
-Note:
-
-\begin{description}
-\item[(1)] The lock returned is in the format \code{(\var{mode}, \var{len},
-\var{start}, \var{whence}, \var{pid})} where \var{mode} is a character
-representing the type of lock ('r' or 'w'). This modifier prevents a
-request from being granted; it is for query purposes only.
-\end{description}
-
-Format characters for the \method{flags()} method have the following
-meanings:
-
-\begin{tableii}{c|l}{samp}{Format}{Meaning}
- \lineii{a}{append only flag}
- \lineii{c}{close on exec flag}
- \lineii{n}{no delay flag (also called non-blocking flag)}
- \lineii{s}{synchronization flag}
-\end{tableii}
-
-In addition the following modifiers can be added to the format:
-
-\begin{tableiii}{c|l|c}{samp}{Modifier}{Meaning}{Notes}
- \lineiii{!}{turn the specified flags 'off', instead of the default 'on'}{(1)}
- \lineiii{=}{replace the flags, instead of the default 'OR' operation}{(1)}
- \lineiii{?}{return a string in which the characters represent the flags that
- are set.}{(2)}
-\end{tableiii}
-
-\noindent
-Notes:
-
-\begin{description}
-\item[(1)] The \samp{!} and \samp{=} modifiers are mutually exclusive.
-
-\item[(2)] This string represents the flags after they may have been altered
-by the same call.
-\end{description}
-
-Examples:
-
-\begin{verbatim}
-import posixfile
-
-file = posixfile.open('/tmp/test', 'w')
-file.lock('w|')
-...
-file.lock('u')
-file.close()
-\end{verbatim}