commit cf4600e1582f3001a26b4430a5ffbfe23b3ff4d1
author Kelvin Zhang <zhangkelvin@google.com> Tue Oct 27 15:50:33 2020 -0400
committer Kelvin Zhang <zhangkelvin@google.com> Mon Jan 04 18:51:11 2021 -0500
tree 05b10c5bf52e457d20c93bf04ce9d2fe8fb205c4
parent 3265b317b39edea86b5351029092b7728ca8461b

Use string_view for pref interface to reduce copy

If you pass in a static string literal like "Hello World!", then with
parameter type of const string& you need to construct a new string
object, requiring a copy. It will also require a copy if your data is in
another container, for example std::vector<char> . In update_engine, we
store manifest bytes in std::vector, and sometimes we want to save that
manifest to disk. This CL can help us reduce copy of the manifest(up to
2MB).

Test: treehugger
Change-Id: I70feb4c0673c174fd47f02c4bd41994f74cda743

common/prefs.h

diff --git a/common/prefs.h b/common/prefs.h
index d6ef668..93477dd 100644
--- a/common/prefs.h
+++ b/common/prefs.h
@@ -19,6 +19,7 @@
 
 #include <map>
 #include <string>
+#include <string_view>
 #include <vector>
 
 #include <base/files/file_path.h>
@@ -49,7 +50,7 @@
 
     // Set the value of the key named |key| to |value| regardless of the
     // previous value. Returns whether the operation succeeded.
-    virtual bool SetKey(const std::string& key, const std::string& value) = 0;
+    virtual bool SetKey(const std::string& key, std::string_view value) = 0;
 
     // Returns whether the key named |key| exists.
     virtual bool KeyExists(const std::string& key) const = 0;
@@ -66,7 +67,7 @@
 
   // PrefsInterface methods.
   bool GetString(const std::string& key, std::string* value) const override;
-  bool SetString(const std::string& key, const std::string& value) override;
+  bool SetString(const std::string& key, std::string_view value) override;
   bool GetInt64(const std::string& key, int64_t* value) const override;
   bool SetInt64(const std::string& key, const int64_t value) override;
   bool GetBoolean(const std::string& key, bool* value) const override;
@@ -123,7 +124,7 @@
     bool GetKey(const std::string& key, std::string* value) const override;
     bool GetSubKeys(const std::string& ns,
                     std::vector<std::string>* keys) const override;
-    bool SetKey(const std::string& key, const std::string& value) override;
+    bool SetKey(const std::string& key, std::string_view value) override;
     bool KeyExists(const std::string& key) const override;
     bool DeleteKey(const std::string& key) override;
 
@@ -163,7 +164,7 @@
     bool GetKey(const std::string& key, std::string* value) const override;
     bool GetSubKeys(const std::string& ns,
                     std::vector<std::string>* keys) const override;
-    bool SetKey(const std::string& key, const std::string& value) override;
+    bool SetKey(const std::string& key, std::string_view value) override;
     bool KeyExists(const std::string& key) const override;
     bool DeleteKey(const std::string& key) override;