Fix for #2854. "BEGIN EXCLUSIVE" excludes other shared cache users from using the database. (CVS 4642)

FossilOrigin-Name: 2e59b1d07ee422bd799b5b7aeea44ebc998d9481

manifest

@@ -1,5 +1,5 @@
-C Fix\ssome\sissues\swith\slemon.\s\sTickets\s#2852\sand\s#2835.\s(CVS\s4641)
+C Fix\sfor\s#2854.\s"BEGIN\sEXCLUSIVE"\sexcludes\sother\sshared\scache\susers\sfrom\susing\sthe\sdatabase.\s(CVS\s4642)
-D 2007-12-21T00:02:11
+D 2007-12-21T04:47:26
 F Makefile.arm-wince-mingw32ce-gcc ac5f7b2cef0cd850d6f755ba6ee4ab961b1fadf7
 F Makefile.in 30789bf70614bad659351660d76b8e533f3340e9
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -83,9 +83,9 @@ F src/analyze.c fd1a3d756c1a20fca3c505bed0398f4cdca83cb8
 F src/attach.c a01d55157d46a1234909f3a7f21fb09549c947bd
 F src/auth.c c8b2ab5c8bad4bd90ed7c294694f48269162c627
 F src/btmutex.c 5d39da37c9d1282f3c6f9967afae6a34ee36b7ff
-F src/btree.c 10cc24011d5602ad332fa8c579a036e678274ee8
+F src/btree.c bef8ceec858b167bd0ce0863fe0bdd527126c213
 F src/btree.h 19dcf5ad23c17b98855da548e9a8e3eb4429d5eb
-F src/btreeInt.h 68ec997e34e426093f706da965c147ece75185b9
+F src/btreeInt.h 1c5a9da165718ef7de81e35ce9ab5d9ba9283f76
 F src/build.c 580561a0d9e070ff2741f3b115cae51c1ef08260
 F src/callback.c 77b302b0d41468dcda78c70e706e5b84577f0fa0
 F src/complete.c 4cf68fd75d60257524cbe74f87351b9848399131
@@ -482,6 +482,7 @@ F test/tkt2817.test 709a2201a5590bf56cb97f6fb168a62282203fd1
 F test/tkt2820.test 017fdee33aaef7abc092beab6088816f1942304b
 F test/tkt2822.test 8b1526b1e5b0d38a1a993f7828fbb81759093686
 F test/tkt2832.test cd56dc66bb31898b7eb2146baa5bde2eb80f96fe
+F test/tkt2854.test aebd5a9904d36d1ef7a074fc5e7c7da3ab00c32a
 F test/trace.test 75ffc1b992c780d054748a656e3e7fd674f18567
 F test/trans.test b73289992b46d38d9479ecc4fdc03d8edb2413dc
 F test/trigger1.test 7c13f39ca36f529bf856e05c7d004fc0531d48b4
@@ -601,7 +602,7 @@ F www/tclsqlite.tcl 8be95ee6dba05eabcd27a9d91331c803f2ce2130
 F www/vdbe.tcl 87a31ace769f20d3627a64fa1fade7fed47b90d0
 F www/version3.tcl 890248cf7b70e60c383b0e84d77d5132b3ead42b
 F www/whentouse.tcl fc46eae081251c3c181bd79c5faef8195d7991a5
-P d3efec148968538e225f5716359a6a25e8941362
+P 5283e0d1467e0fc0ebbd1be553b5a8762e9c7975
-R 85004d42a22e2eebf7a2858fba477cd5
+R e37b64edde771d68293d63348dff6a3a
-U drh
+U danielk1977
-Z ad03768828df010e4ad9480b93fc71b4
+Z 9a8d28eb42d02907bda6dd836ef8b3b4

manifest.uuid

@@ -1 +1 @@
-5283e0d1467e0fc0ebbd1be553b5a8762e9c7975
+2e59b1d07ee422bd799b5b7aeea44ebc998d9481

src/btree.c

@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btree.c,v 1.433 2007/12/13 21:54:11 drh Exp $
+** $Id: btree.c,v 1.434 2007/12/21 04:47:26 danielk1977 Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** See the header comment on "btreeInt.h" for additional information.
@@ -103,6 +103,13 @@ static int queryTableLock(Btree *p, Pgno iTab, u8 eLock){
     return SQLITE_OK;
   }
 
+  /* If some other connection is holding an exclusive lock, the
+  ** requested lock may not be obtained.
+  */
+  if( pBt->pExclusive && pBt->pExclusive!=p ){
+    return SQLITE_LOCKED;
+  }
+
   /* This (along with lockTable()) is where the ReadUncommitted flag is
   ** dealt with. If the caller is querying for a read-lock and the flag is
   ** set, it is unconditionally granted - even if there are write-locks
@@ -212,13 +219,15 @@ static int lockTable(Btree *p, Pgno iTable, u8 eLock){
 ** procedure) held by Btree handle p.
 */
 static void unlockAllTables(Btree *p){
-  BtLock **ppIter = &p->pBt->pLock;
+  BtShared *pBt = p->pBt;
+  BtLock **ppIter = &pBt->pLock;
 
   assert( sqlite3BtreeHoldsMutex(p) );
   assert( p->sharable || 0==*ppIter );
 
   while( *ppIter ){
     BtLock *pLock = *ppIter;
+    assert( pBt->pExclusive==0 || pBt->pExclusive==pLock->pBtree );
     if( pLock->pBtree==p ){
       *ppIter = pLock->pNext;
       sqlite3_free(pLock);
@@ -226,6 +235,10 @@ static void unlockAllTables(Btree *p){
       ppIter = &pLock->pNext;
     }
   }
+
+  if( pBt->pExclusive==p ){
+    pBt->pExclusive = 0;
+  }
 }
 #endif /* SQLITE_OMIT_SHARED_CACHE */
 
@@ -1850,6 +1863,18 @@ int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
     goto trans_begun;
   }
 
+#ifndef SQLITE_OMIT_SHARED_CACHE
+  if( wrflag>1 ){
+    BtLock *pIter;
+    for(pIter=pBt->pLock; pIter; pIter=pIter->pNext){
+      if( pIter->pBtree!=p ){
+        rc = SQLITE_BUSY;
+        goto trans_begun;
+      }
+    }
+  }
+#endif
+
   do {
     if( pBt->pPage1==0 ){
       rc = lockBtree(pBt);
@@ -1882,6 +1907,12 @@ int sqlite3BtreeBeginTrans(Btree *p, int wrflag){
     if( p->inTrans>pBt->inTransaction ){
       pBt->inTransaction = p->inTrans;
     }
+#ifndef SQLITE_OMIT_SHARED_CACHE
+    if( wrflag>1 ){
+      assert( !pBt->pExclusive );
+      pBt->pExclusive = p;
+    }
+#endif
   }
 
 

src/btreeInt.h

@@ -9,7 +9,7 @@
 **    May you share freely, never taking more than you give.
 **
 *************************************************************************
-** $Id: btreeInt.h,v 1.14 2007/12/07 18:55:28 drh Exp $
+** $Id: btreeInt.h,v 1.15 2007/12/21 04:47:26 danielk1977 Exp $
 **
 ** This file implements a external (disk-based) database using BTrees.
 ** For a detailed discussion of BTrees, refer to
@@ -395,6 +395,7 @@ struct BtShared {
   int nRef;             /* Number of references to this structure */
   BtShared *pNext;      /* Next on a list of sharable BtShared structs */
   BtLock *pLock;        /* List of locks held on this shared-btree struct */
+  Btree *pExclusive;    /* Btree with an EXCLUSIVE lock on the whole db */
 #endif
 };
 

test/tkt2854.test

@@ -0,0 +1,140 @@
+# 2007 December 20
+#
+# 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: tkt2854.test,v 1.1 2007/12/21 04:47:27 danielk1977 Exp $
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+db close
+
+ifcapable !shared_cache {
+  finish_test
+  return
+}
+
+set ::enable_shared_cache [sqlite3_enable_shared_cache 1]
+
+# Open 3 database connections. Connection "db" and "db2" share a cache.
+# Connection "db3" has its own cache.
+#
+do_test tkt2854-1.1 {
+  sqlite3 db test.db
+  sqlite3 db2 test.db
+  sqlite3 db3 ./test.db
+
+  db eval {
+    CREATE TABLE abc(a, b, c);
+  }
+} {}
+
+# Check that an exclusive lock cannot be obtained if some other 
+# shared-cache connection has a read-lock on a table.
+#
+do_test tkt2854-1.2 {
+  execsql { 
+    BEGIN;
+    SELECT * FROM abc;
+  } db2
+} {}
+do_test tkt2854-1.3 {
+  catchsql { BEGIN EXCLUSIVE } db
+} {1 {database is locked}}
+do_test tkt2854-1.4 {
+  execsql { SELECT * FROM abc } db3
+} {}
+do_test tkt2854-1.5 {
+  catchsql { INSERT INTO abc VALUES(1, 2, 3) } db3
+} {1 {database is locked}}
+do_test tkt2854-1.6 {
+  execsql { COMMIT } db2
+} {}
+
+# Check that an exclusive lock prevents other shared-cache users from
+# starting a transaction.
+#
+do_test tkt2854-1.7 {
+  set ::DB2 [sqlite3_connection_pointer db2]
+  set ::STMT1 [sqlite3_prepare $DB2 "SELECT * FROM abc" -1 TAIL]
+  set ::STMT2 [sqlite3_prepare $DB2 "BEGIN EXCLUSIVE" -1 TAIL]
+  set ::STMT3 [sqlite3_prepare $DB2 "BEGIN IMMEDIATE" -1 TAIL]
+  set ::STMT4 [sqlite3_prepare $DB2 "BEGIN" -1 TAIL]
+  set ::STMT5 [sqlite3_prepare $DB2 "COMMIT" -1 TAIL]
+  execsql { BEGIN EXCLUSIVE } db
+} {}
+do_test tkt2854-1.8 {
+  catchsql { BEGIN EXCLUSIVE } db2
+} {1 {database schema is locked: main}}
+do_test tkt2854-1.9 {
+  catchsql { BEGIN IMMEDIATE } db2
+} {1 {database schema is locked: main}}
+do_test tkt2854-1.10 {
+  # This fails because the schema of main cannot be verified.
+  catchsql { BEGIN } db2
+} {1 {database schema is locked: main}}
+
+# Check that an exclusive lock prevents other shared-cache users from
+# reading the database. Use stored statements so that the error occurs
+# at the b-tree level, not the schema level.
+#
+do_test tkt2854-1.11 {
+  list [sqlite3_step $::STMT1] [sqlite3_finalize $::STMT1]
+} {SQLITE_ERROR SQLITE_LOCKED}
+do_test tkt2854-1.12 {
+  list [sqlite3_step $::STMT2] [sqlite3_finalize $::STMT2]
+} {SQLITE_BUSY SQLITE_BUSY}
+do_test tkt2854-1.13 {
+  list [sqlite3_step $::STMT3] [sqlite3_finalize $::STMT3]
+} {SQLITE_BUSY SQLITE_BUSY}
+do_test tkt2854-1.14 {
+  # A regular "BEGIN" doesn't touch any databases. So it succeeds.
+  list [sqlite3_step $::STMT4] [sqlite3_finalize $::STMT4]
+} {SQLITE_DONE SQLITE_OK}
+do_test tkt2854-1.15 {
+  # As does a COMMIT.
+  list [sqlite3_step $::STMT5] [sqlite3_finalize $::STMT5]
+} {SQLITE_DONE SQLITE_OK}
+
+# Try to read the database using connection "db3" (which does not share
+# a cache with "db"). The database should be locked.
+do_test tkt2854-1.16 {
+  catchsql { SELECT * FROM abc } db3
+} {1 {database is locked}}
+do_test tkt2854-1.17 {
+  execsql { COMMIT } db
+} {}
+do_test tkt2854-1.18 {
+  execsql { SELECT * FROM abc } db2
+} {}
+
+# Check that if an attempt to obtain an exclusive lock fails because an
+# attached db cannot be locked, the internal exclusive flag used by
+# shared-cache users is correctly cleared.
+do_test tkt2854-1.19 {
+  file delete -force test2.db test2.db-journal
+  sqlite3 db4 test2.db
+  execsql { CREATE TABLE def(d, e, f) } db4
+  execsql { ATTACH 'test2.db' AS aux } db
+} {}
+do_test tkt2854-1.20 {
+  execsql {BEGIN IMMEDIATE} db4
+  catchsql {BEGIN EXCLUSIVE} db
+} {1 {database is locked}}
+do_test tkt2854-1.21 {
+  execsql {SELECT * FROM abc} db2
+} {}
+
+db close
+db2 close
+db3 close
+db4 close
+sqlite3_enable_shared_cache $::enable_shared_cache
+finish_test
+