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Public Member Functions | Protected Member Functions
libdar::cache Class Reference

#include <cache.hpp>

Inherits libdar::generic_file.

List of all members.

Public Member Functions

 cache (generic_file &hidden, bool shift_mode, U_I size=102400)
 cache (const cache &ref)
const cacheoperator= (const cache &ref)
void change_to_read_write ()
bool skippable (skippability direction, const infinint &amount)
bool skip (const infinint &pos)
bool skip_to_eof ()
 skip to the end of file
bool skip_relative (S_I x)
 skip relatively to the current position
infinint get_position () const
 get the current read/write position

Protected Member Functions

void inherited_read_ahead (const infinint &amount)
U_I inherited_read (char *a, U_I size)
 implementation of read() operation
void inherited_write (const char *a, U_I size)
 implementation of the write() operation
void inherited_sync_write ()
 write down any pending data
void inherited_flush_read ()
void inherited_terminate ()
 destructor-like call, except that it is allowed to throw exceptions

Detailed Description

the cache class implements a fixed length read/write caching mechanism

it is intended to reduce context switches when no compression is used and when reading or writing catalogue through a pipe. The catalogue read and write is done by calling dump/constructor methods of the many objects that a catalogue contains. This makes a lot of small reads or writes, which make very poor performances when used over the network through a pipe to ssh. When compression is used, the problem disapears as the compression engine gather these many small reads or writes into much bigger ones. This in only when there is no compression or encryption that this class is useful (and used). Another target of class cache is to provide limited skippability when data is read of written to pipe (which do not have any skippability)

Definition at line 52 of file cache.hpp.


Member Function Documentation

void libdar::cache::inherited_flush_read ( ) [inline, protected, virtual]

reset internal engine, flush caches in order to read the data at current position

Note:
when the object relies on external object or system object to fetch the data from for reading, when a call to (inherited_)flush_read() occurs, the current object must not assume that any previously read data is still valid if it has internal buffers or the like and it should flush them asap. This call must not propagate the flush_read to any other gneric_file object it could rely on

Implements libdar::generic_file.

Definition at line 77 of file cache.hpp.

U_I libdar::cache::inherited_read ( char *  a,
U_I  size 
) [protected, virtual]

implementation of read() operation

Parameters:
[in,out]awhere to put the data to read
[in]sizesays how much data to read
Returns:
the exact amount of data read and put into 'a'
Note:
read as much byte as requested, up to end of file stays blocked if not enough data is available and EOF not yet met. May return less data than requested only if EOF as been reached. in other worlds, EOF is reached when returned data is stricly less than the requested data Any problem shall be reported by throwing an exception.

Implements libdar::generic_file.

void libdar::cache::inherited_read_ahead ( const infinint amount) [inline, protected, virtual]

tells the object that several calls to read() will follow to probably obtain at least the given amount of data

Parameters:
[in]amountis the maximum expected amount of data that is known to be read
Note:
this call may be implemented as a do-nothing call, its presence is only to allow optimization when possible, like in multi-threaded environment

Implements libdar::generic_file.

Definition at line 73 of file cache.hpp.

References libdar::generic_file::read_ahead().

void libdar::cache::inherited_sync_write ( ) [inline, protected, virtual]

write down any pending data

Note:
called after sanity checks from generic_file::sync_write() this method's role is to write down any data pending for writing in the current object it has not to be propagated to other gneric_file object this object could rely on

Implements libdar::generic_file.

Definition at line 76 of file cache.hpp.

void libdar::cache::inherited_terminate ( ) [inline, protected, virtual]

destructor-like call, except that it is allowed to throw exceptions

Note:
this method must never be called directly but using terminate() instead, generic_file class manages it to never be called more than once

Implements libdar::generic_file.

Definition at line 78 of file cache.hpp.

void libdar::cache::inherited_write ( const char *  a,
U_I  size 
) [protected, virtual]

implementation of the write() operation

Parameters:
[in]awhat data to write
[in]sizeamount of data to write
Note:
must either write all data or report an error by throwing an exception

Implements libdar::generic_file.

bool libdar::cache::skip ( const infinint pos) [virtual]

skip at the absolute position

Parameters:
[in]posthe offset in byte where next read/write operation must start
Returns:
true if operation was successfull and false if the requested position is not valid (after end of file)
Note:
if requested position is not valid the reading/writing cursor must be set to the closest valid position

Implements libdar::generic_file.

bool libdar::cache::skippable ( skippability  direction,
const infinint amount 
) [virtual]

whether the implementation is able to skip

Note:
the capability to skip does not mean that skip_relative() or skip() will succeed, but rather that the inherited class implementation does not by construction forbid the requested skip (like inherited class providing a generic_file interface of an anonymous pipe for example)

Implements libdar::generic_file.


The documentation for this class was generated from the following file:
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