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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