sql: Document sql::StatementID's thread safety properties.
This CL:
1) Extracts StatementID from sql/connection.{h,cc} into its own files
sql/statement_id.{h,cc}.
2) Adds tests specifically targeting sql::StatementID.
3) Replaces passing StatementID by const reference with passing by
value.
4) Removes the StatementID constructor that takes a name, and updates
the call sites to use the source file+line constructor.
Bug: 863724
Change-Id: I5bc6e160fe294189d3e9a2baa8f6be61b21c38d2
Reviewed-on: https://chromium-review.googlesource.com/1137915
Commit-Queue: Victor Costan <[email protected]>
Reviewed-by: Scott Violet <[email protected]>
Reviewed-by: Chris Mumford <[email protected]>
Cr-Commit-Position: refs/heads/master@{#576295}diff --git a/sql/statement_id.h b/sql/statement_id.h
new file mode 100644
index 0000000..f52b725d
--- /dev/null
+++ b/sql/statement_id.h
@@ -0,0 +1,56 @@
+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SQL_STATEMENT_ID_H_
+#define SQL_STATEMENT_ID_H_
+
+#include <cstddef>
+
+#include "sql/sql_export.h"
+
+namespace sql {
+
+// Identifies a compiled SQLite statement in a statement cache.
+//
+// This is a value type with the same performance characteristics as
+// std::string_view. Instances are thread-unsafe, but not thread-hostile.
+//
+// StatementID instances should be constructed by using the SQL_FROM_HERE
+// macro, which produces an unique ID based on the source file name and line.
+class SQL_EXPORT StatementID {
+ public:
+ // Creates an ID representing a line in the source tree.
+ //
+ // SQL_FROM_HERE should be preferred to calling this constructor directly.
+ //
+ // |source_file| should point to a C-style string that lives for the duration
+ // of the program.
+ explicit StatementID(const char* source_file, size_t source_line) noexcept
+ : source_file_(source_file), source_line_(source_line) {}
+
+ // Copying intentionally allowed.
+ StatementID(const StatementID&) noexcept = default;
+ StatementID& operator=(const StatementID&) noexcept = default;
+
+ // Facilitates storing StatementID instances in maps.
+ bool operator<(const StatementID& rhs) const noexcept;
+
+ private:
+ // Instances cannot be immutable because they support being used as map keys.
+ //
+ // It seems tempting to merge source_file_ and source_line_ in a single
+ // source_location_ member, and to have SQL_FROM_HERE use C++ preprocessor
+ // magic to generate strings like "sql/connection.cc:42". This causes a
+ // non-trivial binary size increase, because Chrome uses -fmerge-constants and
+ // SQL_FROM_HERE tends to be used many times in the same few files.
+ const char* source_file_;
+ size_t source_line_;
+};
+
+} // namespace sql
+
+// Produces a StatementID based on the current line in the source tree.
+#define SQL_FROM_HERE sql::StatementID(__FILE__, __LINE__)
+
+#endif // SQL_STATEMENT_ID_H_
