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ost::SharedFile

NAME

ost::SharedFile −

This class defines a database I/O file service that can be shared by multiple processes.

SYNOPSIS

#include <file.h>

Inherits ost::RandomFile.

Public Member Functions

SharedFile (const char *path)
Open or create a new database file.

SharedFile
(const SharedFile &file)
Create a shared file as a duplicate of an existing shared file.

virtual ~SharedFile ()
Close and finish a database file.

Error restart
(void)
Restart an existing database; close and re-open.

Error fetch
(char *address=NULL, ccxx_size_t length=0, off_t position=-1)
Lock and Fetch a portion of the file into physical memory.

Error update
(char *address=NULL, ccxx_size_t length=0, off_t position=-1)
Update a portion of a file from physical memory.

Error clear
(ccxx_size_t length=0, off_t pos=-1)
Clear a lock held from a previous fetch operation without updating.

Error append
(char *address=NULL, ccxx_size_t length=0)
Add new data to the end of the file.

off_t getPosition (void)
Fetch the current file position marker for this thread.

bool operator++ (void)
bool operator-- (void)

Detailed Description

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.

SharedFile is used when a database may be shared between multiple processes. SharedFile automatically applies low level byte-range ’file
locks’, and provides an interface to fetch and release byte-range locked portions of a file.

Author:

David Sugar <dyfet AT ostel DOT com> This class defines a database I/O file service that can be shared by multiple processes.

Constructor & Destructor Documentation

ost::SharedFile::SharedFile (const char * path)
Open or create a new database file. You should also use Initial.

Parameters:

path pathname of database to open.

ost::SharedFile::SharedFile (const SharedFile & file)
Create a shared file as a duplicate of an existing shared file. Parameters:

file original file.

virtual ost::SharedFile::~SharedFile () [virtual]
Close and finish a database file.

Member Function Documentation

Error ost::SharedFile::append (char * address = NULL, ccxx_size_t length = 0)
Add new data to the end of the file. Locks file during append.

Parameters:

address address to use, or NULL if same as last I/O.
length
length to use, or 0 if same as last I/O.

Error ost::SharedFile::clear (ccxx_size_t length = 0, off_t pos = -1)
Clear a lock held from a previous fetch operation without updating. Returns:

errSuccess on success.

Parameters:

length length to use, or 0 if same as last I/O.
pos
file position to use or -1 if same as last I/O.

Error ost::SharedFile::fetch (char * address = NULL, ccxx_size_t length = 0, off_t position = -1)
Lock and Fetch a portion of the file into physical memory. This can use state information to fetch the current record multiple times.

Returns:

errSuccess on success.

Parameters:

address address to use, or NULL if same as last I/O.
length
length to use, or 0 if same as last I/O.
position
file position to use -1 if same as last I/O.

off_t ost::SharedFile::getPosition (void)
Fetch the current file position marker for this thread. Returns:

file position offset.

bool ost::SharedFile::operator++ (void)
bool ost::SharedFile::operator-- (void)
Error ost::SharedFile::restart (void)
[inline, virtual]
Restart an existing database; close and re-open. Returns:

errSuccess if successful.

Reimplemented from ost::RandomFile.

Error ost::SharedFile::update (char * address = NULL, ccxx_size_t length = 0, off_t position = -1)
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.

Returns:

errSuccess on success.

Parameters:

address address to use, or NULL if same as last I/O.
length
length to use, or 0 if same as last I/O.
position
file position to use or -1 if same as last I/O.

Author

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