Index: src/btree.c
==================================================================
--- src/btree.c
+++ src/btree.c
@@ -7,11 +7,11 @@
 **    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 1.648 2009/07/02 07:47:33 danielk1977 Exp $
+** $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.
 */
@@ -79,10 +79,11 @@
   ** So define the lock related functions as no-ops.
   */
   #define querySharedCacheTableLock(a,b,c) SQLITE_OK
   #define setSharedCacheTableLock(a,b,c) SQLITE_OK
   #define clearAllSharedCacheTableLocks(a)
+  #define downgradeAllSharedCacheTableLocks(a)
   #define hasSharedCacheTableLock(a,b,c,d) 1
   #define hasReadConflicts(a, b) 0
 #endif
 
 #ifndef SQLITE_OMIT_SHARED_CACHE
@@ -391,10 +392,25 @@
     ** 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;
+    for(pLock=pBt->pLock; pLock; pLock=pLock->pNext){
+      assert( pLock->eLock==READ_LOCK || pLock->pBtree==p );
+      pLock->eLock = READ_LOCK;
+    }
+  }
+}
+
 #endif /* SQLITE_OMIT_SHARED_CACHE */
 
 static void releasePage(MemPage *pPage);  /* Forward reference */
 
 /*
@@ -2898,10 +2914,52 @@
     rc = sqlite3PagerCommitPhaseOne(pBt->pPager, zMaster, 0);
     sqlite3BtreeLeave(p);
   }
   return rc;
 }
+
+/*
+** This function is called from both BtreeCommitPhaseTwo() and BtreeRollback()
+** at the conclusion of a transaction.
+*/
+static void btreeEndTransaction(Btree *p){
+  BtShared *pBt = p->pBt;
+  BtCursor *pCsr;
+  assert( sqlite3BtreeHoldsMutex(p) );
+
+  /* Search for a cursor held open by this b-tree connection. If one exists,
+  ** then the transaction will be downgraded to a read-only transaction
+  ** instead of actually concluded. A subsequent call to CommitPhaseTwo() 
+  ** or Rollback() will finish the transaction and unlock the database.  */
+  for(pCsr=pBt->pCursor; pCsr && pCsr->pBtree!=p; pCsr=pCsr->pNext);
+  assert( pCsr==0 || p->inTrans>TRANS_NONE );
+
+  btreeClearHasContent(pBt);
+  if( pCsr ){
+    downgradeAllSharedCacheTableLocks(p);
+    p->inTrans = TRANS_READ;
+  }else{
+    /* If the handle had any kind of transaction open, decrement the 
+    ** transaction count of the shared btree. If the transaction count 
+    ** reaches 0, set the shared state to TRANS_NONE. The unlockBtreeIfUnused()
+    ** call below will unlock the pager.  */
+    if( p->inTrans!=TRANS_NONE ){
+      clearAllSharedCacheTableLocks(p);
+      pBt->nTransaction--;
+      if( 0==pBt->nTransaction ){
+        pBt->inTransaction = TRANS_NONE;
+      }
+    }
+
+    /* Set the current transaction state to TRANS_NONE and unlock the 
+    ** pager if this call closed the only read or write transaction.  */
+    p->inTrans = TRANS_NONE;
+    unlockBtreeIfUnused(pBt);
+  }
+
+  btreeIntegrity(p);
+}
 
 /*
 ** Commit the transaction currently in progress.
 **
 ** This routine implements the second phase of a 2-phase commit.  The
@@ -2935,31 +2993,11 @@
       return rc;
     }
     pBt->inTransaction = TRANS_READ;
   }
 
-  /* If the handle has any kind of transaction open, decrement the transaction
-  ** count of the shared btree. If the transaction count reaches 0, set
-  ** the shared state to TRANS_NONE. The unlockBtreeIfUnused() call below
-  ** will unlock the pager.
-  */
-  if( p->inTrans!=TRANS_NONE ){
-    clearAllSharedCacheTableLocks(p);
-    pBt->nTransaction--;
-    if( 0==pBt->nTransaction ){
-      pBt->inTransaction = TRANS_NONE;
-    }
-  }
-
-  /* Set the current transaction state to TRANS_NONE and unlock
-  ** the pager if this call closed the only read or write transaction.
-  */
-  btreeClearHasContent(pBt);
-  p->inTrans = TRANS_NONE;
-  unlockBtreeIfUnused(pBt);
-
-  btreeIntegrity(p);
+  btreeEndTransaction(p);
   sqlite3BtreeLeave(p);
   return SQLITE_OK;
 }
 
 /*
@@ -3077,24 +3115,11 @@
     }
     assert( countWriteCursors(pBt)==0 );
     pBt->inTransaction = TRANS_READ;
   }
 
-  if( p->inTrans!=TRANS_NONE ){
-    clearAllSharedCacheTableLocks(p);
-    assert( pBt->nTransaction>0 );
-    pBt->nTransaction--;
-    if( 0==pBt->nTransaction ){
-      pBt->inTransaction = TRANS_NONE;
-    }
-  }
-
-  btreeClearHasContent(pBt);
-  p->inTrans = TRANS_NONE;
-  unlockBtreeIfUnused(pBt);
-
-  btreeIntegrity(p);
+  btreeEndTransaction(p);
   sqlite3BtreeLeave(p);
   return rc;
 }
 
 /*

Index: src/prepare.c
==================================================================
--- src/prepare.c
+++ src/prepare.c
@@ -11,11 +11,11 @@
 *************************************************************************
 ** This file contains the implementation of the sqlite3_prepare()
 ** interface, and routines that contribute to loading the database schema
 ** from disk.
 **
-** $Id: prepare.c,v 1.126 2009/07/02 07:47:33 danielk1977 Exp $
+** $Id: prepare.c,v 1.127 2009/07/02 17:21:58 danielk1977 Exp $
 */
 #include "sqliteInt.h"
 
 /*
 ** Fill the InitData structure with an error message that indicates
@@ -134,11 +134,11 @@
   char const *azArg[4];
   int meta[5];
   InitData initData;
   char const *zMasterSchema;
   char const *zMasterName = SCHEMA_TABLE(iDb);
-  int openedTransaction;
+  int openedTransaction = 0;
 
   /*
   ** The master database table has a structure like this
   */
   static const char master_schema[] = 
@@ -220,12 +220,10 @@
     if( rc!=SQLITE_OK ){
       sqlite3SetString(pzErrMsg, db, "%s", sqlite3ErrStr(rc));
       goto initone_error_out;
     }
     openedTransaction = 1;
-  }else{
-    openedTransaction = 0;
   }
 
   /* Get the database meta information.
   **
   ** Meta values are as follows:

ADDED   test/sharedlock.test
Index: test/sharedlock.test
==================================================================
--- test/sharedlock.test
+++ test/sharedlock.test
@@ -0,0 +1,55 @@
+# 2009 July 2
+#
+# 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: sharedlock.test,v 1.1 2009/07/02 17:21:58 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]
+sqlite3 db  test.db
+sqlite3 db2 test.db
+
+do_test sharedlock-1.1 {
+  execsql {
+    CREATE TABLE t1(a, b);
+    INSERT INTO t1 VALUES(1, 'one');
+    INSERT INTO t1 VALUES(2, 'two');
+  }
+} {}
+
+do_test sharedlock-1.2 {
+  set res [list]
+  db eval { SELECT * FROM t1 ORDER BY rowid } {
+    lappend res $a $b
+    if {$a == 1} { catch { db  eval "INSERT INTO t1 VALUES(3, 'three')" } }
+
+    # This should fail. Connection [db] has a read-lock on t1, which should
+    # prevent connection [db2] from obtaining the write-lock it needs to
+    # modify t1. At one point there was a bug causing the previous INSERT
+    # to drop the read-lock belonging to [db].
+    if {$a == 2} { catch { db2 eval "INSERT INTO t1 VALUES(4, 'four')"  } }
+  }
+  set res
+} {1 one 2 two 3 three}
+
+db close
+db2 close
+
+sqlite3_enable_shared_cache $::enable_shared_cache
+finish_test
+