Use GUID to generate unique temp file names and retire GetTempFileName

base/files/file_util_win.cc

Index: base/files/file_util_win.cc
diff --git a/base/files/file_util_win.cc b/base/files/file_util_win.cc
index 65dc5ce1e2fe7495624cc6d8c16b954395eb11ac..3be02b54368fb1faf6f6154408ef3af0fca2cafe 100644
--- a/base/files/file_util_win.cc
+++ b/base/files/file_util_win.cc
@@ -40,6 +40,34 @@ namespace {
 const DWORD kFileShareAll =
     FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
 
+// An array consists of digits and alphabet. It is used to generate random
+// prefix of a temp file name which is passed to GetTempFileName Windows API.
+const char kAlphaNumberCharSet[] =

[gab, 2017/04/03 16:40:49]

I think you'll need to use FILE_PATH_LITERAL to get the char type that matches
FilePath::StringType on each platform.

[gab, 2017/04/03 16:40:49]

constexpr

[chengx, 2017/04/03 18:35:10]

Done.

[chengx, 2017/04/03 18:35:11]

Done.

+    "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

[gab, 2017/04/03 16:40:49]

Filenames on Windows are case insensitive so don't include upper-case characters
here.

[chengx, 2017/04/03 18:35:10]

Done.

+
+// The length of the temp file name prefix, which is used by GetTempFileName
+// Windows API.
+// GetTempFileName uses up to the first three characters of the input
+// prefix string as the prefix of the file name. Therefore, this constant is
+// set to three.
+// https://msdn.microsoft.com/en-us/library/windows/desktop/aa364991(v=vs.85).aspx
+const int kPrefixLength = 3;

[gab, 2017/04/03 16:40:50]

constexpr

[chengx, 2017/04/03 18:35:11]

Done.

+
+// Get a random prefix with length kPrefixLength of the temp file name.
+// The characters are obtained from kAlphaNumberCharSet.
+FilePath::StringType GetRandomPrefix() {
+  FilePath::StringType temp_file_name_prefix;
+  temp_file_name_prefix.resize(kPrefixLength);
+
+  size_t char_set_length = strlen(kAlphaNumberCharSet);

[gab, 2017/04/03 16:40:50]

inline arraysize(kAlphaNumberCharSet) instead (it's a constexpr)

[chengx, 2017/04/03 18:35:10]

Done.

+
+  srand(time(NULL));
+  for (size_t i = 0; i < kPrefixLength; i++)
+    temp_file_name_prefix[i] = kAlphaNumberCharSet[rand() % char_set_length];

[gab, 2017/04/03 16:40:49]

Use base::RandGenerator(arraysize(kAlphaNumberCharSet));

(don't think you need to seed, would assume Chrome has to seed its generators
when it starts already, though I'm not sure how it does it)

[chengx, 2017/04/03 18:35:10]

Yes, no need to seed here if using base::RandGenerator.

+
+  return temp_file_name_prefix;
+}
+
 // Deletes all files and directories in a path.
 // Returns false on the first failure it encounters.
 bool DeleteFileRecursive(const FilePath& path,
@@ -342,7 +370,13 @@ bool CreateTemporaryFileInDir(const FilePath& dir, FilePath* temp_file) {
 
   wchar_t temp_name[MAX_PATH + 1];
 
-  if (!GetTempFileName(dir.value().c_str(), L"", 0, temp_name)) {
+  // Due to the algorithm used to generate file names, GetTempFileName Windows
+  // API can perform poorly when creating a large number of files with the same
+  // prefix. Therefore, making the prefix random should boost its performance.
+  // https://msdn.microsoft.com/en-us/library/windows/desktop/aa364991(v=vs.85).aspx
+
+  if (!GetTempFileName(dir.value().c_str(), GetRandomPrefix().c_str(), 0,
+                       temp_name)) {
     DPLOG(WARNING) << "Failed to get temporary file name in "
                    << UTF16ToUTF8(dir.value());
     return false;