Changed createTemporaryFile without FD to actually create a file.

Summary:
This commit changes semantics of createUniqueFile and
createTemporaryFile variants that do not return file descriptors.
Previously they only checked if files exist, therefore being subject
to race conditions. Now they will create an empty file to avoid them.

Functions that do not create a file are now called
getPotentiallyUniqueTempFileName and getPotentiallyUniqueFileName.

Reviewers: klimek, bkramer, krasimir, JDevlieghere, espindola

Reviewed By: klimek

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D36827

llvm-svn: 327851

2 files changed, 60 insertions, 10 deletions

diff --git a/llvm/include/llvm/Support/FileSystem.h b/llvm/include/llvm/Support/FileSystem.h
index 499682c16c7..a9b02d9f4e4 100644
--- a/llvm/include/llvm/Support/FileSystem.h
+++ b/llvm/include/llvm/Support/FileSystem.h
@@ -720,9 +720,11 @@ std::error_code createUniqueFile(const Twine &Model, int &ResultFD,
                                  unsigned Mode = all_read | all_write,
                                  sys::fs::OpenFlags Flags = sys::fs::F_RW);
 
-/// @brief Simpler version for clients that don't want an open file.
+/// @brief Simpler version for clients that don't want an open file. An empty
+/// file will still be created.
 std::error_code createUniqueFile(const Twine &Model,
-                                 SmallVectorImpl<char> &ResultPath);
+                                 SmallVectorImpl<char> &ResultPath,
+                                 unsigned Mode = all_read | all_write);
 
 /// Represents a temporary file.
 ///
@@ -775,13 +777,36 @@ std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
                                     SmallVectorImpl<char> &ResultPath,
                                     sys::fs::OpenFlags Flags = sys::fs::F_RW);
 
-/// @brief Simpler version for clients that don't want an open file.
+/// @brief Simpler version for clients that don't want an open file. An empty
+/// file will still be created.
 std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
                                     SmallVectorImpl<char> &ResultPath);
 
 std::error_code createUniqueDirectory(const Twine &Prefix,
                                       SmallVectorImpl<char> &ResultPath);
 
+/// @brief Get a unique name, not currently exisiting in the filesystem. Subject
+/// to race conditions, prefer to use createUniqueFile instead.
+///
+/// Similar to createUniqueFile, but instead of creating a file only
+/// checks if it exists. This function is subject to race conditions, if you
+/// want to use the returned name to actually create a file, use
+/// createUniqueFile instead.
+std::error_code getPotentiallyUniqueFileName(const Twine &Model,
+                                             SmallVectorImpl<char> &ResultPath);
+
+/// @brief Get a unique temporary file name, not currently exisiting in the
+/// filesystem. Subject to race conditions, prefer to use createTemporaryFile
+/// instead.
+///
+/// Similar to createTemporaryFile, but instead of creating a file only
+/// checks if it exists. This function is subject to race conditions, if you
+/// want to use the returned name to actually create a file, use
+/// createTemporaryFile instead.
+std::error_code
+getPotentiallyUniqueTempFileName(const Twine &Prefix, StringRef Suffix,
+                                 SmallVectorImpl<char> &ResultPath);
+
 inline OpenFlags operator|(OpenFlags A, OpenFlags B) {
   return OpenFlags(unsigned(A) | unsigned(B));
 }
diff --git a/llvm/lib/Support/Path.cpp b/llvm/lib/Support/Path.cpp
index f229f23a4f8..ec8a5ca98e5 100644
--- a/llvm/lib/Support/Path.cpp
+++ b/llvm/lib/Support/Path.cpp
@@ -757,9 +757,15 @@ std::error_code createUniqueFile(const Twine &Model, int &ResultFd,
 }
 
 std::error_code createUniqueFile(const Twine &Model,
-                                 SmallVectorImpl<char> &ResultPath) {
-  int Dummy;
-  return createUniqueEntity(Model, Dummy, ResultPath, false, 0, FS_Name);
+                                 SmallVectorImpl<char> &ResultPath,
+                                 unsigned Mode) {
+  int FD;
+  auto EC = createUniqueFile(Model, FD, ResultPath, Mode);
+  if (EC)
+    return EC;
+  // FD is only needed to avoid race conditions. Close it right away.
+  close(FD);
+  return EC;
 }
 
 static std::error_code
@@ -794,8 +800,13 @@ std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
 
 std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
                                     SmallVectorImpl<char> &ResultPath) {
-  int Dummy;
-  return createTemporaryFile(Prefix, Suffix, Dummy, ResultPath, FS_Name);
+  int FD;
+  auto EC = createTemporaryFile(Prefix, Suffix, FD, ResultPath);
+  if (EC)
+    return EC;
+  // FD is only needed to avoid race conditions. Close it right away.
+  close(FD);
+  return EC;
 }
 
 
@@ -804,8 +815,22 @@ std::error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
 std::error_code createUniqueDirectory(const Twine &Prefix,
                                       SmallVectorImpl<char> &ResultPath) {
   int Dummy;
-  return createUniqueEntity(Prefix + "-%%%%%%", Dummy, ResultPath,
-                            true, 0, FS_Dir);
+  return createUniqueEntity(Prefix + "-%%%%%%", Dummy, ResultPath, true, 0,
+                            FS_Dir);
+}
+
+std::error_code
+getPotentiallyUniqueFileName(const Twine &Model,
+                             SmallVectorImpl<char> &ResultPath) {
+  int Dummy;
+  return createUniqueEntity(Model, Dummy, ResultPath, false, 0, FS_Name);
+}
+
+std::error_code
+getPotentiallyUniqueTempFileName(const Twine &Prefix, StringRef Suffix,
+                                 SmallVectorImpl<char> &ResultPath) {
+  int Dummy;
+  return createTemporaryFile(Prefix, Suffix, Dummy, ResultPath, FS_Name);
 }
 
 static std::error_code make_absolute(const Twine &current_directory,