In sqlite3_table_column_metadata(), hold the mutex on all attached BtShared objects while accessing schema objects. Fix for #3679. (CVS 6328)

FossilOrigin-Name: d197afd658eecfc0e24913e5a779c8f1e2a138a6

test/thread004.test

@@ -0,0 +1,80 @@
+# 2009 February 26
+#
+# 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: thread004.test,v 1.1 2009/02/26 07:15:59 danielk1977 Exp $
+
+set testdir [file dirname $argv0]
+
+source $testdir/tester.tcl
+ifcapable !mutex||!shared_cache {
+  return
+}
+source $testdir/thread_common.tcl
+if {[info commands sqlthread] eq "" 
+ || [info commands sqlite3_table_column_metadata] eq ""
+} {
+  return
+}
+
+# Use shared-cache mode for this test.
+# 
+db close
+set ::enable_shared_cache [sqlite3_enable_shared_cache]
+sqlite3_enable_shared_cache 1
+
+# Create a table in database test.db
+#
+sqlite3 db test.db
+do_test thread004-1.1 {
+  execsql { CREATE TABLE t1(a, b, c) }
+} {}
+
+do_test thread004-1.2 {
+
+  set ThreadOne {
+    set iStart [clock_seconds]
+    while {[clock_seconds]<$iStart+20} {
+      set ::DB [sqlite3_open test.db]
+      sqlite3_close $::DB
+    }
+  }
+  set ThreadTwo {
+    set ::DB [sqlite3_open test.db]
+    set iStart [clock_seconds]
+    set nErr 0
+    while {[clock_seconds] <$iStart+20} {
+      incr nErr [catch {sqlite3_table_column_metadata $::DB main t1 a}]
+    }
+    sqlite3_close $::DB
+    set nErr
+  }
+  
+  # Run two threads. The first thread opens and closes database test.db
+  # repeatedly. Each time this happens, the in-memory schema used by
+  # all connections to test.db is discarded.
+  #
+  # The second thread calls sqlite3_table_column_metadata() over and
+  # over again. Each time it is called, the database schema is loaded
+  # if it is not already in memory. At one point this was crashing.
+  #
+  unset -nocomplain finished
+  thread_spawn finished(1) $thread_procs $ThreadOne
+  thread_spawn finished(2) $thread_procs $ThreadTwo
+  
+  foreach t {1 2} {
+    if {![info exists finished($t)]} { vwait finished($t) }
+  }
+
+  set finished(2)
+} {0}
+sqlite3_enable_shared_cache $::enable_shared_cache
+finish_test
+