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

   Additional Inherited Members

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@ostel.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 (caddr_t 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 (caddr_t 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 (caddr_t 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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