rewrite_to_chrome_style: Add a lock file when writing replacements.

tools/clang/rewrite_to_chrome_style/RewriteToChromeStyle.cpp

 // Copyright 2015 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.
 //
 // Changes Blink-style names to Chrome-style names. Currently transforms:
 //   fields:
 //     int m_operationCount => int operation_count_
 //   variables (including parameters):
 //     int mySuperVariable => int my_super_variable
 //   constants:
 //     const int maxThings => const int kMaxThings
 //   free functions and methods:
 //     void doThisThenThat() => void DoThisAndThat()
 
 #include <assert.h>
 #include <algorithm>
 #include <fstream>
 #include <memory>
 #include <string>
 #include <unordered_map>
 #include <unordered_set>
 
+#if defined(_WIN32)
+#include <windows.h>
+#else
+#include <sys/file.h>
+#include <unistd.h>
+#endif
+
 #include "clang/AST/ASTContext.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 #include "clang/ASTMatchers/ASTMatchersMacros.h"
 #include "clang/Basic/CharInfo.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Frontend/FrontendActions.h"
 #include "clang/Lex/Lexer.h"
 #include "clang/Tooling/CommonOptionsParser.h"
 #include "clang/Tooling/Refactoring.h"
@@ skipping 471 matching lines @@
       &replacements);
   match_finder.addMatcher(constructor_initializer_matcher,
                           &constructor_initializer_rewriter);
 
   std::unique_ptr<clang::tooling::FrontendActionFactory> factory =
       clang::tooling::newFrontendActionFactory(&match_finder);
   int result = tool.run(factory.get());
   if (result != 0)
     return result;
 
+#if defined(_WIN32)
+  OFSTRUCT lockfd_out;
+  HFILE lockfd = OpenFile("rewrite-sym.lock", &lockfd_out, OF_CREATE);

[dcheng, 2016/01/26 07:04:15]

It might be slightly more robust to use CreateFile(). From MSDN:
This function has limited capabilities and is not recommended. For new
application development, use the CreateFile function.

(specifically, there's a 128 character path limit... which we probably won't
hit, but it'd be nice not to have to worry about hitting it by accident while
we're trying to get the tree reopened)

[danakj, 2016/01/26 23:34:52]

Done. I think.

+  OVERLAPPED lock_out = {};
+  LockFileEx(lockfd, LOCKFILE_EXCLUSIVE_LOCK, 0, 1, 0, &lock_out);
+#else
+  int lockfd = open("rewrite-sym.lock", O_RDWR | O_CREAT, 0666);
+  while (flock(lockfd, LOCK_EX)) {  // :D
+  }
+#endif
+
   std::ofstream replacement_db_file("rewrite-sym.txt",
                                     std::ios_base::out | std::ios_base::app);
   for (const auto& p : field_decl_rewriter.replacement_names())
     replacement_db_file << "var:" << p.first << ":" << p.second << "\n";
   for (const auto& p : var_decl_rewriter.replacement_names())
     replacement_db_file << "var:" << p.first << ":" << p.second << "\n";
   for (const auto& p : function_decl_rewriter.replacement_names())
     replacement_db_file << "fun:" << p.first << ":" << p.second << "\n";
   for (const auto& p : method_decl_rewriter.replacement_names())
     replacement_db_file << "fun:" << p.first << ":" << p.second << "\n";
   replacement_db_file.close();
 
+#if defined(_WIN32)
+  UnlockFile(lockfd, 0, 0, 1, 0);

[dcheng, 2016/01/26 07:04:15]

Nit: UnlockFileEx for symmetry? The parameters are already pretty mysterious
looking.

[danakj, 2016/01/26 23:34:52]

Done.

+  CloseHandle(lockfd);
+#else
+  flock(lockfd, LOCK_UN);
+  close(lockfd);
+#endif
+
   // Serialization format is documented in tools/clang/scripts/run_tool.py
   llvm::outs() << "==== BEGIN EDITS ====\n";
   for (const auto& r : replacements) {
     std::string replacement_text = r.getReplacementText().str();
     std::replace(replacement_text.begin(), replacement_text.end(), '\n', '\0');
     llvm::outs() << "r:::" << r.getFilePath() << ":::" << r.getOffset()
                  << ":::" << r.getLength() << ":::" << replacement_text << "\n";
   }
   llvm::outs() << "==== END EDITS ====\n";
 
   return 0;
 }