/* 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); } } }
/* ** 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){ Btree *pLater; /* 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; /* In most cases, we should be able to acquire the lock we ** want without having to go throught 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){ if( p->sharable ){ assert( p->wantToLock>0 ); p->wantToLock--; if( p->wantToLock==0 ){ unlockBtreeMutex(p); } } }
/* ** 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); } } }
/* ** Enter a mutex on the given BTree object. ** 在给定的B树对象上输入一个互斥锁。 ** 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. ** 如果对象不可共享,那么不需要互斥锁并且这个程序是无操作的。这个潜在的互斥锁是非递归的。 ** 但是在Btree.wantToLock中保持对参数的计数,因此这歌接口的操作是递归的。 ** ** 为了避免死锁,多个btree以相同的顺序被所有数据库连接锁定。p->pNext是其他属于相同数据库连接的B树列表 ** 作为B树p,p->pNext需要在p后被锁。如果在p上不能的锁,那么首先在p->pNext上解除其他所有锁,然后等待 ** 直到在p上的锁可用,接着对需要加锁的所有后续B树重新加锁。 */ void sqlite3BtreeEnter(Btree *p){ Btree *pLater; /* 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. ** 在B树上进行基本的完整性检查。通过pNext和pPrev连接的B树列表应该 ** 按Btree.pBt的值进行排序。列表的所有元素都应属于相同的连接。只有共享的B树在列表中。 */ 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 检查锁的一致性*/ assert( !p->locked || p->wantToLock>0 ); assert( p->sharable || p->wantToLock==0 ); /* We should already hold a lock on the database connection 在数据库连接上应该已经持有一个锁*/ assert( sqlite3_mutex_held(p->db->mutex) ); /* Unless the database is sharable and unlocked, then BtShared.db ** should already be set correctly. ** 如果数据库是可共享的并且没有被锁,那么BtShared.db应该已经被正确设置。 */ assert( (p->locked==0 && p->sharable) || p->pBt->db==p->db ); if( !p->sharable ) return; p->wantToLock++; if( p->locked ) return; /* In most cases, we should be able to acquire the lock we ** want without having to go throught the ascending lock ** procedure that follows. Just be sure not to block. ** 在大多数情况下,我们应该能得到锁,我们想要的这个锁不必通过追溯在其后的锁进程。只是对块不确定。 */ 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. ** 为了避免死锁,首先释放所有更大BtShared地址的锁。然后获得我们的锁。 ** 接着再次获取我们曾在提升顺序中持有的其他锁。 */ 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); } } }