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ost::SharedFile

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

#include <file.h>

Inherits ost::RandomFile.


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)

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.

Open or create a new database file. You should also use Initial.

Parameters:

path pathname of database to open.

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

Parameters:

file original file.

Close and finish a database file.

Error ost::SharedFile::append (caddr_taddress = NULL, ccxx_size_tlength = 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_tlength = 0, off_tpos = -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_taddress = NULL, ccxx_size_tlength = 0, off_tposition = -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.

Fetch the current file position marker for this thread.

Returns:

file position offset.

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_taddress = NULL, ccxx_size_tlength = 0, off_tposition = -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.

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