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Must hold mutex on the destination during backups. Add documentation to

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warn programmers that attempting to use the destination connection during
a backup can lead to deadlock. (CVS 6246)

FossilOrigin-Name: 5f6c06b974f26532264467ace603b6f1f830fba9
This commit is contained in:
drh
2009-02-03 21:13:07 +00:00
parent 39070edbab
commit 662c58c9ba
4 changed files with 23 additions and 15 deletions
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14
src/backup.c
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@@ -12,7 +12,7 @@
** This file contains the implementation of the sqlite3_backup_XXX()
** API functions and the related features.
**
** $Id: backup.c,v 1.1 2009/02/03 16:51:25 danielk1977 Exp $
** $Id: backup.c,v 1.2 2009/02/03 21:13:08 drh Exp $
*/
#include "sqliteInt.h"
#include "btreeInt.h"
@@ -126,9 +126,12 @@ sqlite3_backup *sqlite3_backup_init(
sqlite3_backup *p; /* Value to return */
/* Lock the source database handle. The destination database
** handle is not locked. The user is required to ensure that no
** handle is not locked in this routine, but it is locked in
** sqlite3_backup_step(). The user is required to ensure that no
** other thread accesses the destination handle for the duration
** of the backup operation.
** of the backup operation. Any attempt to use the destination
** database connection while a backup is in progress may cause
** a malfunction or a deadlock.
*/
sqlite3_mutex_enter(pSrcDb->mutex);
@@ -248,6 +251,7 @@ int sqlite3_backup_step(sqlite3_backup *p, int nPage){
sqlite3_mutex_enter(p->pSrcDb->mutex);
sqlite3BtreeEnter(p->pSrc);
sqlite3_mutex_enter(p->pDestDb->mutex);
rc = p->rc;
if( rc==SQLITE_OK ){
@@ -403,6 +407,7 @@ int sqlite3_backup_step(sqlite3_backup *p, int nPage){
p->rc = rc;
}
}
sqlite3_mutex_leave(p->pDestDb->mutex);
sqlite3BtreeLeave(p->pSrc);
sqlite3_mutex_leave(p->pSrcDb->mutex);
return rc;
@@ -420,6 +425,7 @@ int sqlite3_backup_finish(sqlite3_backup *p){
sqlite3_mutex_enter(p->pSrcDb->mutex);
sqlite3BtreeEnter(p->pSrc);
mutex = p->pSrcDb->mutex;
sqlite3_mutex_enter(p->pDestDb->mutex);
/* Detach this backup from the source pager. */
if( p->pDestDb ){
@@ -439,6 +445,7 @@ int sqlite3_backup_finish(sqlite3_backup *p){
sqlite3Error(p->pDestDb, rc, 0);
/* Exit the mutexes and free the backup context structure. */
sqlite3_mutex_leave(p->pDestDb->mutex);
sqlite3BtreeLeave(p->pSrc);
if( p->pDestDb ){
sqlite3_free(p);
@@ -556,4 +563,3 @@ int sqlite3BtreeCopyFile(Btree *pTo, Btree *pFrom){
return rc;
}
#endif /* SQLITE_OMIT_VACUUM */