\section{ost::Shared\-File Class Reference}
\label{classost_1_1_shared_file}\index{ost::SharedFile@{ost::SharedFile}}
This class defines a database I/O file service that can be shared by multiple processes.This class defines a database I/O file service that can be shared by multiple processes.  


{\tt \#include $<$file.h$>$}

Inheritance diagram for ost::Shared\-File::\begin{figure}[H]
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\includegraphics[height=3cm]{classost_1_1_shared_file}
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\subsection*{Public Member Functions}
\begin{CompactItemize}
\item 
{\bf Shared\-File} (const char $\ast$path)
\begin{CompactList}\small\item\em Open or create a new database file. \item\end{CompactList}\item 
{\bf Shared\-File} (const {\bf Shared\-File} \&file)
\begin{CompactList}\small\item\em Create a shared file as a duplicate of an existing shared file. \item\end{CompactList}\item 
virtual {\bf $\sim$Shared\-File} ()
\begin{CompactList}\small\item\em Close and finish a database file. \item\end{CompactList}\item 
{\bf Error} {\bf restart} (void)
\begin{CompactList}\small\item\em Restart an existing database; close and re-open. \item\end{CompactList}\item 
{\bf Error} {\bf fetch} (char $\ast$address=NULL, {\bf ccxx\_\-size\_\-t} length=0, off\_\-t position=-1)
\begin{CompactList}\small\item\em Lock and Fetch a portion of the file into physical memory. \item\end{CompactList}\item 
{\bf Error} {\bf update} (char $\ast$address=NULL, {\bf ccxx\_\-size\_\-t} length=0, off\_\-t position=-1)
\begin{CompactList}\small\item\em Update a portion of a file from physical memory. \item\end{CompactList}\item 
{\bf Error} {\bf clear} ({\bf ccxx\_\-size\_\-t} length=0, off\_\-t pos=-1)
\begin{CompactList}\small\item\em Clear a lock held from a previous fetch operation without updating. \item\end{CompactList}\item 
{\bf Error} {\bf append} (char $\ast$address=NULL, {\bf ccxx\_\-size\_\-t} length=0)
\begin{CompactList}\small\item\em Add new data to the end of the file. \item\end{CompactList}\item 
off\_\-t {\bf get\-Position} (void)
\begin{CompactList}\small\item\em Fetch the current file position marker for this thread. \item\end{CompactList}\item 
bool {\bf operator++} (void)
\item 
bool {\bf operator--} (void)
\end{CompactItemize}


\subsection{Detailed Description}
This class defines a database I/O file service that can be shared by multiple processes.This class defines a database I/O file service that can be shared by multiple processes. 

Each thread should access a dup of the database object, and mutex locks can be used to preserve transaction integrety if multiple threads are used.

{\bf Shared\-File}{\rm (p.\,\pageref{classost_1_1_shared_file})} is used when a database may be shared between multiple processes. {\bf Shared\-File}{\rm (p.\,\pageref{classost_1_1_shared_file})} automatically applies low level byte-range \char`\"{}file locks\char`\"{}, and provides an interface to fetch and release byte-range locked portions of a file.

\begin{Desc}
\item[Author:]David Sugar $<${\tt dyfet@ostel.com}$>$ \end{Desc}




\subsection{Constructor \& Destructor Documentation}
\index{ost::SharedFile@{ost::Shared\-File}!SharedFile@{SharedFile}}
\index{SharedFile@{SharedFile}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}ost::Shared\-File::Shared\-File (const char $\ast$ {\em path})}\label{classost_1_1_shared_file_c5b43aef08de67e5f8fd88bf7e5f6a80}


Open or create a new database file. 

You should also use Initial.

\begin{Desc}
\item[Parameters:]
\begin{description}
\item[{\em path}]pathname of database to open. \end{description}
\end{Desc}
\index{ost::SharedFile@{ost::Shared\-File}!SharedFile@{SharedFile}}
\index{SharedFile@{SharedFile}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}ost::Shared\-File::Shared\-File (const {\bf Shared\-File} \& {\em file})}\label{classost_1_1_shared_file_c13ee6d8e5fb10dcf5ce6e9e12f54ae9}


Create a shared file as a duplicate of an existing shared file. 

\begin{Desc}
\item[Parameters:]
\begin{description}
\item[{\em file}]original file. \end{description}
\end{Desc}
\index{ost::SharedFile@{ost::Shared\-File}!~SharedFile@{$\sim$SharedFile}}
\index{~SharedFile@{$\sim$SharedFile}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}virtual ost::Shared\-File::$\sim$Shared\-File ()\hspace{0.3cm}{\tt  [virtual]}}\label{classost_1_1_shared_file_4001a868611c75292113daded7c0a585}


Close and finish a database file. 



\subsection{Member Function Documentation}
\index{ost::SharedFile@{ost::Shared\-File}!append@{append}}
\index{append@{append}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}{\bf Error} ost::Shared\-File::append (char $\ast$ {\em address} = {\tt NULL}, {\bf ccxx\_\-size\_\-t} {\em length} = {\tt 0})}\label{classost_1_1_shared_file_7169520f6cabe7de4626ab2b0c1d138f}


Add new data to the end of the file. 

Locks file during append.

\begin{Desc}
\item[Parameters:]
\begin{description}
\item[{\em address}]address to use, or NULL if same as last I/O. \item[{\em length}]length to use, or 0 if same as last I/O. \end{description}
\end{Desc}
\index{ost::SharedFile@{ost::Shared\-File}!clear@{clear}}
\index{clear@{clear}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}{\bf Error} ost::Shared\-File::clear ({\bf ccxx\_\-size\_\-t} {\em length} = {\tt 0}, off\_\-t {\em pos} = {\tt -1})}\label{classost_1_1_shared_file_c36a90105fb7435b498dcd72fa2473dd}


Clear a lock held from a previous fetch operation without updating. 

\begin{Desc}
\item[Returns:]err\-Success on success. \end{Desc}
\begin{Desc}
\item[Parameters:]
\begin{description}
\item[{\em length}]length to use, or 0 if same as last I/O. \item[{\em pos}]file position to use or -1 if same as last I/O. \end{description}
\end{Desc}
\index{ost::SharedFile@{ost::Shared\-File}!fetch@{fetch}}
\index{fetch@{fetch}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}{\bf Error} ost::Shared\-File::fetch (char $\ast$ {\em address} = {\tt NULL}, {\bf ccxx\_\-size\_\-t} {\em length} = {\tt 0}, off\_\-t {\em position} = {\tt -1})}\label{classost_1_1_shared_file_a4f875ec058a85297a62e30af397d014}


Lock and Fetch a portion of the file into physical memory. 

This can use state information to fetch the current record multiple times.

\begin{Desc}
\item[Returns:]err\-Success on success. \end{Desc}
\begin{Desc}
\item[Parameters:]
\begin{description}
\item[{\em address}]address to use, or NULL if same as last I/O. \item[{\em length}]length to use, or 0 if same as last I/O. \item[{\em position}]file position to use -1 if same as last I/O. \end{description}
\end{Desc}
\index{ost::SharedFile@{ost::Shared\-File}!getPosition@{getPosition}}
\index{getPosition@{getPosition}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}off\_\-t ost::Shared\-File::get\-Position (void)}\label{classost_1_1_shared_file_b7ac91d6a8ded5c7236297784353a300}


Fetch the current file position marker for this thread. 

\begin{Desc}
\item[Returns:]file position offset. \end{Desc}
\index{ost::SharedFile@{ost::Shared\-File}!operator++@{operator++}}
\index{operator++@{operator++}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}bool ost::Shared\-File::operator++ (void)}\label{classost_1_1_shared_file_a7a0de19328f2d2c2ed8d06f7e5fa884}


\index{ost::SharedFile@{ost::Shared\-File}!operator--@{operator--}}
\index{operator--@{operator--}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}bool ost::Shared\-File::operator-- (void)}\label{classost_1_1_shared_file_9bab1e7719f2f608d719e99125bdc8e8}


\index{ost::SharedFile@{ost::Shared\-File}!restart@{restart}}
\index{restart@{restart}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}{\bf Error} ost::Shared\-File::restart (void)\hspace{0.3cm}{\tt  [inline, virtual]}}\label{classost_1_1_shared_file_254c43de705b9ad9f5d24536b6cff1e0}


Restart an existing database; close and re-open. 

\begin{Desc}
\item[Returns:]err\-Success if successful. \end{Desc}


Reimplemented from {\bf ost::Random\-File} {\rm (p.\,\pageref{classost_1_1_random_file_e78c71b1e3fab5861bc9fdae595829a7})}.\index{ost::SharedFile@{ost::Shared\-File}!update@{update}}
\index{update@{update}!ost::SharedFile@{ost::Shared\-File}}
\subsubsection{\setlength{\rightskip}{0pt plus 5cm}{\bf Error} ost::Shared\-File::update (char $\ast$ {\em address} = {\tt NULL}, {\bf ccxx\_\-size\_\-t} {\em length} = {\tt 0}, off\_\-t {\em position} = {\tt -1})}\label{classost_1_1_shared_file_5ace5a51d0da7c56a252e3f26efeff67}


Update a portion of a file from physical memory. 

This can use state information to commit the last read record. The current lock is also cleared.

\begin{Desc}
\item[Returns:]err\-Success on success. \end{Desc}
\begin{Desc}
\item[Parameters:]
\begin{description}
\item[{\em address}]address to use, or NULL if same as last I/O. \item[{\em length}]length to use, or 0 if same as last I/O. \item[{\em position}]file position to use or -1 if same as last I/O. \end{description}
\end{Desc}


The documentation for this class was generated from the following file:\begin{CompactItemize}
\item 
{\bf file.h}\end{CompactItemize}