SQLite

/*
** 2004 April 6
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** $Id: btree.c,v 1.649 2009/07/02 17:21:58 danielk1977 Exp $
**
** This file implements a external (disk-based) database using BTrees.
** See the header comment on "btreeInt.h" for additional information.
** Including a description of file format and an overview of operation.
*/
#include "btreeInt.h"

static int querySharedCacheTableLock(Btree *p, Pgno iTab, u8 eLock){
  BtShared *pBt = p->pBt;
  BtLock *pIter;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
  assert( p->db!=0 );

  
  /* If requesting a write-lock, then the Btree must have an open write
  ** transaction on this file. And, obviously, for this to be so there 
  ** must be an open write transaction on the file itself.
  */
  assert( eLock==READ_LOCK || (p==pBt->pWriter && p->inTrans==TRANS_WRITE) );
  assert( eLock==READ_LOCK || pBt->inTransaction==TRANS_WRITE );

  ** requested lock may not be obtained.
  */
  if( pBt->pWriter!=p && pBt->isExclusive ){
    sqlite3ConnectionBlocked(p->db, pBt->pWriter->db);
    return SQLITE_LOCKED_SHAREDCACHE;
  }

  /* This (along with setSharedCacheTableLock()) is where
  ** the ReadUncommitted flag is dealt with.
  ** If the caller is querying for a read-lock on any table
  ** other than the sqlite_master table (table 1) and if the ReadUncommitted
  ** flag is set, then the lock granted even if there are write-locks
  ** on the table. If a write-lock is requested, the ReadUncommitted flag
  ** is not considered.
  **
  ** In function setSharedCacheTableLock(), if a read-lock is demanded and the 
  ** ReadUncommitted flag is set, no entry is added to the locks list 
  ** (BtShared.pLock).
  **
  ** To summarize: If the ReadUncommitted flag is set, then read cursors
  ** on non-schema tables do not create or respect table locks. The locking
  ** procedure for a write-cursor does not change.
  */
  if( 
    0==(p->db->flags&SQLITE_ReadUncommitted) || 
    eLock==WRITE_LOCK ||
    iTab==MASTER_ROOT
  ){
    for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
      /* The condition (pIter->eLock!=eLock) in the following if(...) 
      ** statement is a simplification of:
      **
      **   (eLock==WRITE_LOCK || pIter->eLock==WRITE_LOCK)
      **
      ** since we know that if eLock==WRITE_LOCK, then no other connection
      ** may hold a WRITE_LOCK on any table in this file (since there can
      ** only be a single writer).
      */
      assert( pIter->eLock==READ_LOCK || pIter->eLock==WRITE_LOCK );
      assert( eLock==READ_LOCK || pIter->pBtree==p || pIter->eLock==READ_LOCK);
      if( pIter->pBtree!=p && pIter->iTable==iTab && pIter->eLock!=eLock ){
        sqlite3ConnectionBlocked(p->db, pIter->pBtree->db);
        if( eLock==WRITE_LOCK ){
          assert( p==pBt->pWriter );
          pBt->isPending = 1;
        }
        return SQLITE_LOCKED_SHAREDCACHE;
      }
    }
  }
  return SQLITE_OK;
}
#endif /* !SQLITE_OMIT_SHARED_CACHE */

#ifndef SQLITE_OMIT_SHARED_CACHE

  BtLock *pLock = 0;
  BtLock *pIter;

  assert( sqlite3BtreeHoldsMutex(p) );
  assert( eLock==READ_LOCK || eLock==WRITE_LOCK );
  assert( p->db!=0 );







  /* This is a no-op if the shared-cache is not enabled */
  if( !p->sharable ){
    return SQLITE_OK;
  }

  assert( SQLITE_OK==querySharedCacheTableLock(p, iTable, eLock) );

  /* If the read-uncommitted flag is set and a read-lock is requested on
  ** a non-schema table, then the lock is always granted.  Return early
  ** without adding an entry to the BtShared.pLock list. See
  ** comment in function querySharedCacheTableLock() for more info
  ** on handling the ReadUncommitted flag.
  */
  if( 
    (p->db->flags&SQLITE_ReadUncommitted) && 
    (eLock==READ_LOCK) &&
    iTable!=MASTER_ROOT
  ){
    return SQLITE_OK;
  }

  /* First search the list for an existing lock on this table. */
  for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
    if( pIter->iTable==iTable && pIter->pBtree==p ){
      pLock = pIter;
      break;
    }
  }

    ** If there is not currently a writer, then BtShared.isPending must
    ** be zero already. So this next line is harmless in that case.
    */
    pBt->isPending = 0;
  }
}




static void downgradeAllSharedCacheTableLocks(Btree *p){
  BtShared *pBt = p->pBt;
  if( pBt->pWriter==p ){
    BtLock *pLock;
    pBt->pWriter = 0;
    pBt->isExclusive = 0;
    pBt->isPending = 0;

** free pages is not visible.  So Cookie[0] is the same as Meta[1].
*/
void sqlite3BtreeGetMeta(Btree *p, int idx, u32 *pMeta){
  BtShared *pBt = p->pBt;

  sqlite3BtreeEnter(p);
  assert( p->inTrans>TRANS_NONE );
  assert( SQLITE_OK==querySharedCacheTableLock(p, 1, READ_LOCK) );
  assert( pBt->pPage1 );
  assert( idx>=0 && idx<=15 );

  *pMeta = get4byte(&pBt->pPage1->aData[36 + idx*4]);

  /* If auto-vacuum is disabled in this build and this is an auto-vacuum
  ** database, mark the database as read-only.  */

**
** Various scripts scan this source file in order to generate HTML
** documentation, headers files, or other derived files.  The formatting
** of the code in this file is, therefore, important.  See other comments
** in this file for details.  If in doubt, do not deviate from existing
** commenting and indentation practices when changing or adding code.
**
** $Id: vdbe.c,v 1.868 2009/07/02 07:47:33 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include "vdbeInt.h"

/*
** The following global variable is incremented every time a cursor
** moves, either by the OP_SeekXX, OP_Next, or OP_Prev opcodes.  The test

**
** P2 contains the root-page of the table to lock.
**
** P4 contains a pointer to the name of the table being locked. This is only
** used to generate an error message if the lock cannot be obtained.
*/
case OP_TableLock: {
  int p1;
  u8 isWriteLock;

  p1 = pOp->p1; 
  isWriteLock = (u8)pOp->p3;
  assert( p1>=0 && p1<db->nDb );
  assert( (p->btreeMask & (1<<p1))!=0 );
  assert( isWriteLock==0 || isWriteLock==1 );
  rc = sqlite3BtreeLockTable(db->aDb[p1].pBt, pOp->p2, isWriteLock);
  if( (rc&0xFF)==SQLITE_LOCKED ){
    const char *z = pOp->p4.z;
    sqlite3SetString(&p->zErrMsg, db, "database table is locked: %s", z);

  }
  break;
}
#endif /* SQLITE_OMIT_SHARED_CACHE */

#ifndef SQLITE_OMIT_VIRTUALTABLE
/* Opcode: VBegin * * * P4 *