[sql] Use memory-mapped I/O for sql::Connection.

sql/connection_unittest.cc

Index: sql/connection_unittest.cc
diff --git a/sql/connection_unittest.cc b/sql/connection_unittest.cc
index 10a15a868908965d893ce4952388bd09688e4e19..5ce591a360d68f1cef18f72170a27fb2650bf787 100644
--- a/sql/connection_unittest.cc
+++ b/sql/connection_unittest.cc
@@ -4,10 +4,12 @@
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
+#include "base/files/memory_mapped_file.h"
 #include "base/files/scoped_file.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
 #include "base/metrics/statistics_recorder.h"
+#include "base/strings/stringprintf.h"
 #include "base/test/histogram_tester.h"
 #include "sql/connection.h"
 #include "sql/correct_sql_test_base.h"
@@ -1298,4 +1300,54 @@ TEST_F(SQLConnectionTest, TimeUpdateTransaction) {
   EXPECT_EQ(0, samples->sum());
 }
 
-}  // namespace
+// Make sure that OS file writes to a mmap'ed file are reflected in the memory
+// mapping of a memory-mapped file.  Normally SQLite writes to memory-mapped
+// files using memcpy(), which should stay consistent.  Our SQLite is slightly
+// patched to mmap read only, then write using OS file writes.  If the
+// memory-mapped version doesn't reflect the OS file writes, SQLite's
+// memory-mapped I/O should be disabled on this platform.
+TEST_F(SQLConnectionTest, MmapTest) {
+  {
+    sql::Statement s(db().GetUniqueStatement("PRAGMA mmap_size"));
+    ASSERT_TRUE(s.Step());
+    EXPECT_GT(s.ColumnInt64(0), 0);
+  }
+  db().Close();
+  const uint32 kFlags =
+      base::File::FLAG_OPEN_ALWAYS|base::File::FLAG_READ|base::File::FLAG_WRITE;
+  base::File f(db_path(), kFlags);
+  ASSERT_TRUE(f.IsValid());
+
+  // Create a file with a block of '0', a block of '1', and a block of '2'.
+  char buf[4096];
+  memset(buf, '0', sizeof(buf));
+  ASSERT_EQ(f.Write(0*sizeof(buf), buf, sizeof(buf)), (int)sizeof(buf));
+
+  memset(buf, '1', sizeof(buf));
+  ASSERT_EQ(f.Write(1*sizeof(buf), buf, sizeof(buf)), (int)sizeof(buf));
+
+  memset(buf, '2', sizeof(buf));
+  ASSERT_EQ(f.Write(2*sizeof(buf), buf, sizeof(buf)), (int)sizeof(buf));
+
+  // mmap the file and verify that everything looks right.
+  base::MemoryMappedFile m;
+  ASSERT_TRUE(m.Initialize(db_path()));
+
+  memset(buf, '0', sizeof(buf));
+  ASSERT_EQ(0, memcmp(buf, m.data() + 0*sizeof(buf), sizeof(buf)));
+
+  memset(buf, '1', sizeof(buf));
+  ASSERT_EQ(0, memcmp(buf, m.data() + 1*sizeof(buf), sizeof(buf)));
+
+  memset(buf, '2', sizeof(buf));
+  ASSERT_EQ(0, memcmp(buf, m.data() + 2*sizeof(buf), sizeof(buf)));
+
+  // Scribble some '3' into the first page of the file, and verify that it looks
+  // the same in the memory mapping.
+  memset(buf, '3', sizeof(buf));
+  ASSERT_EQ(f.Write(0*sizeof(buf), buf, sizeof(buf)), (int)sizeof(buf));
+  ASSERT_EQ(0, memcmp(buf, m.data() + 0*sizeof(buf), sizeof(buf)));
+
+}
+
+}  // namespace sql