/*---
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---*/
/**
 * @file
 * Manages the page buffer

    pageManager - Provides cached page handling, delegates to blob
    manager when necessary.  Doesn't implement an eviction policy.
    That is left to a cacheManager.  (Multiple cacheManagers can be
    used with a single page manager.)

 
  @todo Allow error checking!  
 
  @todo Make linux provide a better version of malloc().  We need to
  directly DMA pages into and out of userland, or setup mmap() so
  that it takes a flag that makes it page mmapped() pages to swap
  instead of back to disk. (munmap() and msync() would still hit the
  on-disk copy)
 
  @todo Refactoring for lock manager
 
  Possible interface for lockManager:

       Define three classes of objects that the lock manager is interested in:

         Transactions,
	 Operations,
	 Predicates.

       LLADD already has operations and transactions, and these can be
       relatively unchanged.  Predicates are read only operations that
       return a set of tuples.  Tread() is the simplest predicate.
       Index scans provide a motivating example.  

       See http://research.microsoft.com/%7Eadya/pubs/icde00.pdf
       (Generalized Isolation Level Definitions, Adya, Liskov, O'Neil,
       2000) for a theoretical discussion of general locking schemes..

       Locking functions can return errors such as DEADLOCK, etc.
       When such a value is returned, the transaction aborts, and an
       error is passed up to the application.

 * @ingroup LLADD_CORE
 * $Id$
 */

#ifndef __BUFFERMANAGER_H__
#define __BUFFERMANAGER_H__


#include <lladd/constants.h>
#include <lladd/transactional.h>

/**
   Page is defined in bufferManager.h as an incomplete type to enforce
   an abstraction barrier between page.h and the rest of the system.

   If you need to muck with page internals, first consider the
   implications that doing so has on locking.  In particular, rwlatch
   is currently entirely handled in page.c.
*/
typedef struct Page_s Page_s;
typedef struct Page_s Page;

/**
 * @param pageid ID of the page you want to load
 * @return fully formed Page type
 * @return page with -1 ID if page not found
 */
Page * loadPage(int pageid);

/**
   loadPage aquires a lock when it is called, effectively pinning it
   in memory.  realeasePage releases this lock.
*/
void releasePage(Page * p);


/**
 * initialize buffer manager
 * @return 0 on success
 * @return error code on failure
 */
int bufInit();

/**
 * allocate a record.  This must be done in two phases.  The first
 * phase reserves a slot, and produces a log entry.  The second phase
 * sets up the slot according to the contents of the log entry.
 *
 * Ralloc implements the first phase.
 *
 * @param xid The active transaction.
 * @param size The size of the new record
 * @return allocated record
 *
 * @see slotRalloc the implementation of the second phase.
 */
recordid ralloc(int xid, long size);


/**
 * allocate a record at a given slot.  (Useful for recovery.)
 * 
 * @see ralloc
 */
void slotRalloc(Page * page, lsn_t lsn, recordid rid);

/**
 * @param pageid ID of page you want to read
 * @return LSN found on disk
 */
/*long readLSN(int pageid); */

/**
 * @param xid transaction id @param lsn the lsn that the updated
 * record will reflect.  This is needed by recovery, and undo.  (The
 * lsn of a page must always increase.  Undos are handled by passing
 * in the LSN of the CLR that records the undo.)
 *
 * @param rid recordid where you want to write @param dat data you
 * wish to write
 */
void writeRecord(int xid, Page * page, lsn_t lsn, recordid rid, const void *dat);

/**
 * @param xid transaction ID
 * @param rid
 * @param dat buffer for data
 */
void readRecord(int xid, Page * page, recordid rid, void *dat);

/**
 * all actions necessary when committing a transaction. Can assume that the log
 * has been written as well as any other actions that do not depend on the
 * buffer manager
 *
 * Basicly, this call is here because we used to do copy on write, and
 * it might be useful when locking is implemented.
 *
 * @param xid transaction ID
 * @param lsn the lsn at which the transaction aborted.  (Currently
 * unused, but may be useful for other implementations of the buffer
 * manager.)
 * @return 0 on success
 * @return error code on failure
 */
int bufTransCommit(int xid, lsn_t lsn);

/**
 * 
 * Currently identical to bufTransCommit.
 * 
 * @param xid transaction ID 
 * 
 * @param lsn the lsn at which the transaction aborted.  (Currently
 * unused, but may be useful for other implementations of the buffer
 * manager.)
 *
 * @return 0 on success
 *  
 * @return error code on failure
 */
int bufTransAbort(int xid, lsn_t lsn);

/**
 * will write out any dirty pages, assumes that there are no running
 * transactions
 */
void bufDeinit();

/*void setSlotType(int pageid, int slot, int type); */

#endif