Linux: Try to minimize copying of string information when reading /proc data.

base/process_util_linux.cc

 // Copyright (c) 2011 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.
 
 #include "base/process_util.h"
 
 #include <ctype.h>
 #include <dirent.h>
 #include <dlfcn.h>
 #include <errno.h>
@@ skipping 105 matching lines @@
 
   FilePath stat_file("/proc");
   stat_file = stat_file.Append(base::IntToString(process));
   stat_file = stat_file.Append("status");
   std::string status;
   if (!file_util::ReadFileToString(stat_file, &status))
     return -1;
 
   StringTokenizer tokenizer(status, ":\n");
   ParsingState state = KEY_NAME;
-  std::string last_key_name;
+  StringPiece last_key_name;
   while (tokenizer.GetNext()) {
     switch (state) {
       case KEY_NAME:
-        last_key_name = tokenizer.token();
+        last_key_name = tokenizer.token_piece();
         state = KEY_VALUE;
         break;
       case KEY_VALUE:
         DCHECK(!last_key_name.empty());
         if (last_key_name == "PPid") {
           int ppid;
-          base::StringToInt(tokenizer.token(), &ppid);
+          base::StringToInt(tokenizer.token_piece(), &ppid);
           return ppid;
         }
         state = KEY_NAME;
         break;
     }
   }
   NOTREACHED();
   return -1;
 }
 
@@ skipping 225 matching lines @@
           last_key_name = tokenizer.token_piece();
           state = KEY_VALUE;
           break;
         case KEY_VALUE:
           if (last_key_name.empty()) {
             NOTREACHED();
             return false;
           }
           if (last_key_name.starts_with(private_prefix)) {
             int cur;
-            base::StringToInt(tokenizer.token(), &cur);
+            base::StringToInt(tokenizer.token_piece(), &cur);
             private_kb += cur;
           } else if (last_key_name.starts_with(pss_prefix)) {
             have_pss = true;
             int cur;
-            base::StringToInt(tokenizer.token(), &cur);
+            base::StringToInt(tokenizer.token_piece(), &cur);
             pss_kb += cur;
           }
           state = KEY_NAME;
           break;
       }
     }
   } else {
     // Try statm if smaps is empty because of the SUID sandbox.
     // First we need to get the page size though.
     int page_size_kb = sysconf(_SC_PAGE_SIZE) / 1024;
@@ skipping 84 matching lines @@
   io_file = io_file.Append(base::IntToString(process_));
   io_file = io_file.Append("io");
   if (!file_util::ReadFileToString(io_file, &proc_io_contents))
     return false;
 
   (*io_counters).OtherOperationCount = 0;
   (*io_counters).OtherTransferCount = 0;
 
   StringTokenizer tokenizer(proc_io_contents, ": \n");
   ParsingState state = KEY_NAME;
-  std::string last_key_name;
+  StringPiece last_key_name;
   while (tokenizer.GetNext()) {
     switch (state) {
       case KEY_NAME:
-        last_key_name = tokenizer.token();
+        last_key_name = tokenizer.token_piece();
         state = KEY_VALUE;
         break;
       case KEY_VALUE:
         DCHECK(!last_key_name.empty());
         if (last_key_name == "syscr") {
-          base::StringToInt64(tokenizer.token(),
+          base::StringToInt64(tokenizer.token_piece(),
               reinterpret_cast<int64*>(&(*io_counters).ReadOperationCount));
         } else if (last_key_name == "syscw") {
-          base::StringToInt64(tokenizer.token(),
+          base::StringToInt64(tokenizer.token_piece(),
               reinterpret_cast<int64*>(&(*io_counters).WriteOperationCount));
         } else if (last_key_name == "rchar") {
-          base::StringToInt64(tokenizer.token(),
+          base::StringToInt64(tokenizer.token_piece(),
               reinterpret_cast<int64*>(&(*io_counters).ReadTransferCount));
         } else if (last_key_name == "wchar") {
-          base::StringToInt64(tokenizer.token(),
+          base::StringToInt64(tokenizer.token_piece(),
               reinterpret_cast<int64*>(&(*io_counters).WriteTransferCount));
         }
         state = KEY_NAME;
         break;
     }
   }
   return true;
 }
 
 ProcessMetrics::ProcessMetrics(ProcessHandle process)
@@ skipping 247 matching lines @@
     int score_len = static_cast<int>(score_str.length());
     return (score_len == file_util::WriteFile(oom_file,
                                               score_str.c_str(),
                                               score_len));
   }
 
   return false;
 }
 
 }  // namespace base