Re-land: base: Avoid unnecessary allocations in base::FindThreadID.

base/linux_util.cc

 // Copyright (c) 2012 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/linux_util.h"
 
 #include <dirent.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
 #include <stdlib.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 
 #include <memory>
 #include <vector>
 
 #include "base/command_line.h"
 #include "base/files/file_util.h"
 #include "base/memory/singleton.h"
 #include "base/process/launch.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
+#include "base/strings/string_tokenizer.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/lock.h"
 #include "build/build_config.h"
 
 namespace {
 
 // Not needed for OS_CHROMEOS.
 #if defined(OS_LINUX)
 enum LinuxDistroState {
   STATE_DID_NOT_CHECK  = 0,
@@ skipping 157 matching lines @@
   std::vector<pid_t> tids;
   if (!GetTasksForProcess(pid, &tids))
     return -1;
 
   for (pid_t tid : tids) {
     char buf[256];
     snprintf(buf, sizeof(buf), "/proc/%d/task/%d/status", pid, tid);
     std::string status;
     if (!ReadFileToString(FilePath(buf), &status))
       return -1;
-    StringPairs pairs;
-    SplitStringIntoKeyValuePairs(status, ':', '\n', &pairs);
-    for (const auto& pair : pairs) {
-      const std::string& key = pair.first;
-      const std::string& value_str = pair.second;
-      if (key == "NSpid") {
-        if (ns_pid_supported)
-          *ns_pid_supported = true;
-        std::vector<StringPiece> split_value_str = SplitStringPiece(
-            value_str, "\t", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
-        DCHECK_NE(split_value_str.size(), 0u);
-        int value;
-        // The last value in the list is the PID in the namespace.
-        if (StringToInt(split_value_str.back(), &value) && value == ns_tid) {
-          // The first value in the list is the real PID.
-          if (StringToInt(split_value_str.front(), &value))
-            return value;
-        }
+    StringTokenizer tokenizer(status, "\n");
+    while (tokenizer.GetNext()) {
+      StringPiece value_str(tokenizer.token_piece());
+      if (!value_str.starts_with("NSpid"))
+        continue;
+      if (ns_pid_supported)
+        *ns_pid_supported = true;
+      std::vector<StringPiece> split_value_str = SplitStringPiece(
+          value_str, "\t", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
+      DCHECK_GE(split_value_str.size(), 2u);
+      int value;
+      // The last value in the list is the PID in the namespace.
+      if (StringToInt(split_value_str.back(), &value) && value == ns_tid) {
+        // The second value in the list is the real PID.
+        if (StringToInt(split_value_str[1], &value))
+          return value;
       }
+      break;
     }
   }
   return -1;
 }
 
 }  // namespace base