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-/*
-** 2007 August 27
-**
-** 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.
-**
-*************************************************************************
-**
-** This file contains code used to implement mutexes on Btree objects.
-** This code really belongs in btree.c. But btree.c is getting too
-** big and we want to break it down some. This packaged seemed like
-** a good breakout.
-*/
-#include "btreeInt.h"
-#ifndef SQLITE_OMIT_SHARED_CACHE
-#if SQLITE_THREADSAFE
-
-/*
-** Obtain the BtShared mutex associated with B-Tree handle p. Also,
-** set BtShared.db to the database handle associated with p and the
-** p->locked boolean to true.
-*/
-static void lockBtreeMutex(Btree *p){
- assert( p->locked==0 );
- assert( sqlite3_mutex_notheld(p->pBt->mutex) );
- assert( sqlite3_mutex_held(p->db->mutex) );
-
- sqlite3_mutex_enter(p->pBt->mutex);
- p->pBt->db = p->db;
- p->locked = 1;
-}
-
-/*
-** Release the BtShared mutex associated with B-Tree handle p and
-** clear the p->locked boolean.
-*/
-static void SQLITE_NOINLINE unlockBtreeMutex(Btree *p){
- BtShared *pBt = p->pBt;
- assert( p->locked==1 );
- assert( sqlite3_mutex_held(pBt->mutex) );
- assert( sqlite3_mutex_held(p->db->mutex) );
- assert( p->db==pBt->db );
-
- sqlite3_mutex_leave(pBt->mutex);
- p->locked = 0;
-}
-
-/* Forward reference */
-static void SQLITE_NOINLINE btreeLockCarefully(Btree *p);
-
-/*
-** Enter a mutex on the given BTree object.
-**
-** If the object is not sharable, then no mutex is ever required
-** and this routine is a no-op. The underlying mutex is non-recursive.
-** But we keep a reference count in Btree.wantToLock so the behavior
-** of this interface is recursive.
-**
-** To avoid deadlocks, multiple Btrees are locked in the same order
-** by all database connections. The p->pNext is a list of other
-** Btrees belonging to the same database connection as the p Btree
-** which need to be locked after p. If we cannot get a lock on
-** p, then first unlock all of the others on p->pNext, then wait
-** for the lock to become available on p, then relock all of the
-** subsequent Btrees that desire a lock.
-*/
-void sqlite3BtreeEnter(Btree *p){
- /* Some basic sanity checking on the Btree. The list of Btrees
- ** connected by pNext and pPrev should be in sorted order by
- ** Btree.pBt value. All elements of the list should belong to
- ** the same connection. Only shared Btrees are on the list. */
- assert( p->pNext==0 || p->pNext->pBt>p->pBt );
- assert( p->pPrev==0 || p->pPrev->pBt<p->pBt );
- assert( p->pNext==0 || p->pNext->db==p->db );
- assert( p->pPrev==0 || p->pPrev->db==p->db );
- assert( p->sharable || (p->pNext==0 && p->pPrev==0) );
-
- /* Check for locking consistency */
- assert( !p->locked || p->wantToLock>0 );
- assert( p->sharable || p->wantToLock==0 );
-
- /* We should already hold a lock on the database connection */
- assert( sqlite3_mutex_held(p->db->mutex) );
-
- /* Unless the database is sharable and unlocked, then BtShared.db
- ** should already be set correctly. */
- assert( (p->locked==0 && p->sharable) || p->pBt->db==p->db );
-
- if( !p->sharable ) return;
- p->wantToLock++;
- if( p->locked ) return;
- btreeLockCarefully(p);
-}
-
-/* This is a helper function for sqlite3BtreeLock(). By moving
-** complex, but seldom used logic, out of sqlite3BtreeLock() and
-** into this routine, we avoid unnecessary stack pointer changes
-** and thus help the sqlite3BtreeLock() routine to run much faster
-** in the common case.
-*/
-static void SQLITE_NOINLINE btreeLockCarefully(Btree *p){
- Btree *pLater;
-
- /* In most cases, we should be able to acquire the lock we
- ** want without having to go through the ascending lock
- ** procedure that follows. Just be sure not to block.
- */
- if( sqlite3_mutex_try(p->pBt->mutex)==SQLITE_OK ){
- p->pBt->db = p->db;
- p->locked = 1;
- return;
- }
-
- /* To avoid deadlock, first release all locks with a larger
- ** BtShared address. Then acquire our lock. Then reacquire
- ** the other BtShared locks that we used to hold in ascending
- ** order.
- */
- for(pLater=p->pNext; pLater; pLater=pLater->pNext){
- assert( pLater->sharable );
- assert( pLater->pNext==0 || pLater->pNext->pBt>pLater->pBt );
- assert( !pLater->locked || pLater->wantToLock>0 );
- if( pLater->locked ){
- unlockBtreeMutex(pLater);
- }
- }
- lockBtreeMutex(p);
- for(pLater=p->pNext; pLater; pLater=pLater->pNext){
- if( pLater->wantToLock ){
- lockBtreeMutex(pLater);
- }
- }
-}
-
-
-/*
-** Exit the recursive mutex on a Btree.
-*/
-void sqlite3BtreeLeave(Btree *p){
- assert( sqlite3_mutex_held(p->db->mutex) );
- if( p->sharable ){
- assert( p->wantToLock>0 );
- p->wantToLock--;
- if( p->wantToLock==0 ){
- unlockBtreeMutex(p);
- }
- }
-}
-
-#ifndef NDEBUG
-/*
-** Return true if the BtShared mutex is held on the btree, or if the
-** B-Tree is not marked as sharable.
-**
-** This routine is used only from within assert() statements.
-*/
-int sqlite3BtreeHoldsMutex(Btree *p){
- assert( p->sharable==0 || p->locked==0 || p->wantToLock>0 );
- assert( p->sharable==0 || p->locked==0 || p->db==p->pBt->db );
- assert( p->sharable==0 || p->locked==0 || sqlite3_mutex_held(p->pBt->mutex) );
- assert( p->sharable==0 || p->locked==0 || sqlite3_mutex_held(p->db->mutex) );
-
- return (p->sharable==0 || p->locked);
-}
-#endif
-
-
-#ifndef SQLITE_OMIT_INCRBLOB
-/*
-** Enter and leave a mutex on a Btree given a cursor owned by that
-** Btree. These entry points are used by incremental I/O and can be
-** omitted if that module is not used.
-*/
-void sqlite3BtreeEnterCursor(BtCursor *pCur){
- sqlite3BtreeEnter(pCur->pBtree);
-}
-void sqlite3BtreeLeaveCursor(BtCursor *pCur){
- sqlite3BtreeLeave(pCur->pBtree);
-}
-#endif /* SQLITE_OMIT_INCRBLOB */
-
-
-/*
-** Enter the mutex on every Btree associated with a database
-** connection. This is needed (for example) prior to parsing
-** a statement since we will be comparing table and column names
-** against all schemas and we do not want those schemas being
-** reset out from under us.
-**
-** There is a corresponding leave-all procedures.
-**
-** Enter the mutexes in accending order by BtShared pointer address
-** to avoid the possibility of deadlock when two threads with
-** two or more btrees in common both try to lock all their btrees
-** at the same instant.
-*/
-void sqlite3BtreeEnterAll(sqlite3 *db){
- int i;
- Btree *p;
- assert( sqlite3_mutex_held(db->mutex) );
- for(i=0; i<db->nDb; i++){
- p = db->aDb[i].pBt;
- if( p ) sqlite3BtreeEnter(p);
- }
-}
-void sqlite3BtreeLeaveAll(sqlite3 *db){
- int i;
- Btree *p;
- assert( sqlite3_mutex_held(db->mutex) );
- for(i=0; i<db->nDb; i++){
- p = db->aDb[i].pBt;
- if( p ) sqlite3BtreeLeave(p);
- }
-}
-
-/*
-** Return true if a particular Btree requires a lock. Return FALSE if
-** no lock is ever required since it is not sharable.
-*/
-int sqlite3BtreeSharable(Btree *p){
- return p->sharable;
-}
-
-#ifndef NDEBUG
-/*
-** Return true if the current thread holds the database connection
-** mutex and all required BtShared mutexes.
-**
-** This routine is used inside assert() statements only.
-*/
-int sqlite3BtreeHoldsAllMutexes(sqlite3 *db){
- int i;
- if( !sqlite3_mutex_held(db->mutex) ){
- return 0;
- }
- for(i=0; i<db->nDb; i++){
- Btree *p;
- p = db->aDb[i].pBt;
- if( p && p->sharable &&
- (p->wantToLock==0 || !sqlite3_mutex_held(p->pBt->mutex)) ){
- return 0;
- }
- }
- return 1;
-}
-#endif /* NDEBUG */
-
-#ifndef NDEBUG
-/*
-** Return true if the correct mutexes are held for accessing the
-** db->aDb[iDb].pSchema structure. The mutexes required for schema
-** access are:
-**
-** (1) The mutex on db
-** (2) if iDb!=1, then the mutex on db->aDb[iDb].pBt.
-**
-** If pSchema is not NULL, then iDb is computed from pSchema and
-** db using sqlite3SchemaToIndex().
-*/
-int sqlite3SchemaMutexHeld(sqlite3 *db, int iDb, Schema *pSchema){
- Btree *p;
- assert( db!=0 );
- if( pSchema ) iDb = sqlite3SchemaToIndex(db, pSchema);
- assert( iDb>=0 && iDb<db->nDb );
- if( !sqlite3_mutex_held(db->mutex) ) return 0;
- if( iDb==1 ) return 1;
- p = db->aDb[iDb].pBt;
- assert( p!=0 );
- return p->sharable==0 || p->locked==1;
-}
-#endif /* NDEBUG */
-
-#else /* SQLITE_THREADSAFE>0 above. SQLITE_THREADSAFE==0 below */
-/*
-** The following are special cases for mutex enter routines for use
-** in single threaded applications that use shared cache. Except for
-** these two routines, all mutex operations are no-ops in that case and
-** are null #defines in btree.h.
-**
-** If shared cache is disabled, then all btree mutex routines, including
-** the ones below, are no-ops and are null #defines in btree.h.
-*/
-
-void sqlite3BtreeEnter(Btree *p){
- p->pBt->db = p->db;
-}
-void sqlite3BtreeEnterAll(sqlite3 *db){
- int i;
- for(i=0; i<db->nDb; i++){
- Btree *p = db->aDb[i].pBt;
- if( p ){
- p->pBt->db = p->db;
- }
- }
-}
-#endif /* if SQLITE_THREADSAFE */
-#endif /* ifndef SQLITE_OMIT_SHARED_CACHE */
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