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+# 2013 May 14
+#
+# 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.
+#
+#***********************************************************************
+#
+# Test some specific circumstances to do with shared cache mode.
+#
+
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+if {[run_thread_tests]==0} { finish_test ; return }
+db close
+set ::testprefix sharedA
+
+set ::enable_shared_cache [sqlite3_enable_shared_cache 1]
+
+#-------------------------------------------------------------------------
+#
+do_test 0.1 {
+  sqlite3 db1 test.db
+  sqlite3 db2 test.db
+
+  db1 eval {
+    CREATE TABLE t1(x);
+    INSERT INTO t1 VALUES(randomblob(100));
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    CREATE INDEX i1 ON t1(x);
+  }
+
+  db1 eval {
+    BEGIN;
+    DROP INDEX i1;
+  }
+
+  db2 close
+
+  db1 eval {
+    INSERT INTO t1 SELECT randomblob(100) FROM t1;
+    ROLLBACK;
+    PRAGMA integrity_check;
+  }
+} {ok}
+
+db1 close
+forcedelete test.db
+
+
+#-------------------------------------------------------------------------
+#
+do_test 1.1 {
+  sqlite3 db1 test.db
+  sqlite3 db2 test.db
+  db2 eval {
+    CREATE TABLE t1(x);
+    INSERT INTO t1 VALUES(123);
+  }
+  db1 eval { 
+    SELECT * FROM t1;
+    CREATE INDEX i1 ON t1(x);
+  }
+} {123}
+
+do_test 1.2 {
+  db2 eval { SELECT * FROM t1 ORDER BY x; }
+
+  db1 eval {
+    BEGIN; DROP INDEX i1;
+  }
+  db1 close
+
+  db2 eval { SELECT * FROM t1 ORDER BY x; }
+} {123}
+
+do_test 1.3 {
+  db2 close
+} {}
+
+#-------------------------------------------------------------------------
+#
+# sqlite3RollbackAll() loops through all attached b-trees and rolls
+# back each one separately.  Then if the SQLITE_InternChanges flag is
+# set, it resets the schema.  Both of the above steps must be done
+# while holding a mutex, otherwise another thread might slip in and
+# try to use the new schema with the old data.
+#
+# The following sequence of tests attempt to verify that the actions
+# taken by sqlite3RollbackAll() are thread-atomic (that they cannot be
+# interrupted by a separate thread.)  
+#
+# Note that a TCL interpreter can only be used within the thread in which
+# it was originally created (because it uses thread-local-storage).  
+# The tvfs callbacks must therefore only run on the main thread.  
+# There is some trickery in the read_callback procedure to ensure that
+# this is the case.
+#
+testvfs tvfs
+
+# Set up two databases and two database connections.
+#
+#   db1:  main(test.db), two(test2.db)
+#   db2:  main(test.db)
+#
+# The cache for test.db is shared between db1 and db2.
+#
+do_test 2.1 {
+  forcedelete test.db test.db2
+  sqlite3 db1 test.db -vfs tvfs
+  db1 eval { ATTACH 'test.db2' AS two }
+
+  db1 eval {
+    CREATE TABLE t1(x);
+    INSERT INTO t1 VALUES(1);
+    INSERT INTO t1 VALUES(2);
+    INSERT INTO t1 VALUES(3);
+    CREATE TABLE two.t2(x);
+    INSERT INTO t2 SELECT * FROM t1;
+  }
+
+  sqlite3 db2 test.db -vfs tvfs
+  db2 eval { SELECT * FROM t1 }
+} {1 2 3}
+
+# Create a prepared statement on db2 that will attempt a schema change
+# in test.db.  Meanwhile, start a transaction on db1 that changes
+# the schema of test.db and that creates a rollback journal on test2.db
+#
+do_test 2.2 {
+  set ::STMT [sqlite3_prepare db2 "CREATE INDEX i1 ON t1(x)" -1 tail]
+  db1 eval {
+    BEGIN;
+      CREATE INDEX i1 ON t1(x);
+      INSERT INTO t2 VALUES('value!');
+  }
+} {}
+
+# Set up a callback that will cause db2 to try to execute its
+# schema change when db1 accesses the journal file of test2.db.
+#
+# This callback will be invoked after the content of test.db has
+# be rolled back but before the schema has been reset.  If the
+# sqlite3RollbackAll() operation is not thread-atomic, then the
+# db2 statement in the callback will see old content with the newer
+# schema, which is wrong.
+#
+tvfs filter xRead
+tvfs script read_callback
+unset -nocomplain ::some_time_laster
+unset -nocomplain ::thread_result
+proc read_callback {call file args} { 
+  if {[string match *test.db2-journal $file]} {
+    tvfs filter {}   ;# Ensure that tvfs callbacks to do run on the
+                      # child thread
+    sqlthread spawn ::thread_result [subst -nocommands {
+      sqlite3_step $::STMT
+      set rc [sqlite3_finalize $::STMT]
+    }]
+    after 1000 { set ::some_time_later 1 }
+    vwait ::some_time_later
+  }
+}
+do_test 2.3 { db1 eval ROLLBACK } {}
+
+# Verify that the db2 statement invoked by the callback detected the
+# schema change.
+#
+if {[info exists ::thread_result]==0} { vwait ::thread_result }
+do_test 2.4 { 
+  list $::thread_result [sqlite3_errmsg db2] 
+} {SQLITE_SCHEMA {database schema has changed}}
+
+db1 close
+db2 close
+tvfs delete
+
+sqlite3_enable_shared_cache $::enable_shared_cache
+finish_test