NAME

       ost::MappedFile -

       Create and map a disk file into memory.

SYNOPSIS

       #include <file.h>

       Inherits ost::RandomFile.

   Public Member Functions
       MappedFile (const char *fname, Access mode)
           Open a file for mapping.
       MappedFile (const char *fname, Access mode, size_t size)
           Create if not exists, and map a file of specified size into memory.
       MappedFile (const char *fname, pos_t offset, size_t size, Access mode)
           Map a portion or all of a specified file in the specified shared memory access mode.
       virtual ~MappedFile ()
           Release a mapped section of memory associated with a file.
       void sync (void)
           Synchronize the contents of the mapped portion of memory with the disk file and wait
           for completion.
       void sync (caddr_t address, size_t len)
           Synchronize a segment of memory mapped from a segment fetch.
       void update (size_t offset=0, size_t len=0)
           Map a portion of the memory mapped from the file back to the file and do not wait for
           completion.
       void update (caddr_t address, size_t len)
           Update a mapped region back to disk as specified by address and length.
       void release (caddr_t address, size_t len)
           Release (unmap) a memory segment.
       caddr_t fetch (size_t offset=0)
           Fetch a pointer to an offset within the memory mapped portion of the disk file.
       caddr_t fetch (off_t pos, size_t len)
           Fetch and map a portion of a disk file to a logical memory block.
       bool lock (void)
           Lock the currently mapped portion of a file.
       void unlock (void)
           Unlock a locked mapped portion of a file.
       size_t pageAligned (size_t size)
           Compute map size to aligned page boundry.

   Additional Inherited Members

Detailed Description

       Create and map a disk file into memory.

       This portable class works under both Posix via mmap and under the win32 API. A mapped file
       can be referenced directly by it's memory segment. One can map and unmap portions of a
       file on demand, and update changed memory pages mapped from files immediately through
       sync().

       Author:
           David Sugar dyfet@ostel.com Map a named disk file into memory.

Constructor & Destructor Documentation

   ost::MappedFile::MappedFile (const char *fname, Accessmode)
       Open a file for mapping. More than one segment of a file may be mapped into separate
       regions of memory.

       Parameters:
           fname file name to access for mapping.
           mode access mode to map file.

   ost::MappedFile::MappedFile (const char *fname, Accessmode, size_tsize)
       Create if not exists, and map a file of specified size into memory.

       Parameters:
           fname file name to access for mapping.
           mode access mode to map file.
           size of file to map.

   ost::MappedFile::MappedFile (const char *fname, pos_toffset, size_tsize, Accessmode)
       Map a portion or all of a specified file in the specified shared memory access mode. Valid
       mapping modes include mappedRead, mappedWrite, and mappedReadWrite.

       Parameters:
           fname pathname of file to map into memory.
           offset from start of file to begin mapping in bytes.
           size of mapped area in bytes.
           mode to map file.

   virtual ost::MappedFile::~MappedFile () [virtual]
       Release a mapped section of memory associated with a file. The mapped area is updated back
       to disk.

Member Function Documentation

   caddr_t ost::MappedFile::fetch (size_toffset = 0) [inline]
       Fetch a pointer to an offset within the memory mapped portion of the disk file. This
       really is used for convience of matching operations between Update and Fetch, as one could
       simply have accessed the base pointer where the file was mapped directly.

       Parameters:
           offset from start of mapped memory.

   caddr_t ost::MappedFile::fetch (off_tpos, size_tlen)
       Fetch and map a portion of a disk file to a logical memory block.

       Returns:
           pointer to memory segment.

       Parameters:
           pos offset of file segment to map.
           len size of memory segment to map.

   bool ost::MappedFile::lock (void)
       Lock the currently mapped portion of a file.

       Returns:
           true if pages are locked.

   size_t ost::MappedFile::pageAligned (size_tsize)
       Compute map size to aligned page boundry.

       Parameters:
           size request.

       Returns:
           page aligned size.

   void ost::MappedFile::release (caddr_taddress, size_tlen)
       Release (unmap) a memory segment.

       Parameters:
           address address of memory segment to release.
           len length of memory segment to release.

   void ost::MappedFile::sync (void)
       Synchronize the contents of the mapped portion of memory with the disk file and wait for
       completion. This assures the memory mapped from the file is written back.

   void ost::MappedFile::sync (caddr_taddress, size_tlen)
       Synchronize a segment of memory mapped from a segment fetch.

       Parameters:
           address memory address to update.
           len size of segment.

   void ost::MappedFile::unlock (void)
       Unlock a locked mapped portion of a file.

   void ost::MappedFile::update (size_toffset = 0, size_tlen = 0)
       Map a portion of the memory mapped from the file back to the file and do not wait for
       completion. This is useful when mapping a database file and updating a single record.

       Parameters:
           offset offset into the mapped region of memory.
           len length of partial region (example, record length).

   void ost::MappedFile::update (caddr_taddress, size_tlen)
       Update a mapped region back to disk as specified by address and length.

       Parameters:
           address address of segment.
           len length of segment.

Author

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