[Support/MemoryBuffer] Introduce a boolean parameter (false by default) 'IsVolatile' for the open file functions.

This provides a hint that the file may be changing often so mmap is avoided.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208007 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 50 insertions, 24 deletions

diff --git a/include/llvm/Support/MemoryBuffer.h b/include/llvm/Support/MemoryBuffer.h
index 578c7e8eb8..268041e781 100644
--- a/include/llvm/Support/MemoryBuffer.h
+++ b/include/llvm/Support/MemoryBuffer.h
@@ -67,34 +67,46 @@ public:
   /// MemoryBuffer if successful, otherwise returning null.  If FileSize is
   /// specified, this means that the client knows that the file exists and that
   /// it has the specified size.
+  ///
+  /// \param IsVolatile true indicates that the file may be changing often.
   static error_code getFile(Twine Filename, OwningPtr<MemoryBuffer> &Result,
                             int64_t FileSize = -1,
-                            bool RequiresNullTerminator = true);
+                            bool RequiresNullTerminator = true,
+                            bool IsVolatile = false);
   static error_code getFile(Twine Filename,
                             std::unique_ptr<MemoryBuffer> &Result,
                             int64_t FileSize = -1,
-                            bool RequiresNullTerminator = true);
+                            bool RequiresNullTerminator = true,
+                            bool IsVolatile = false);
 
   /// Given an already-open file descriptor, map some slice of it into a
   /// MemoryBuffer. The slice is specified by an \p Offset and \p MapSize.
   /// Since this is in the middle of a file, the buffer is not null terminated.
+  ///
+  /// \param IsVolatile true indicates that the file may be changing often.
   static error_code getOpenFileSlice(int FD, const char *Filename,
                                      OwningPtr<MemoryBuffer> &Result,
-                                     uint64_t MapSize, int64_t Offset);
+                                     uint64_t MapSize, int64_t Offset,
+                                     bool IsVolatile = false);
   static error_code getOpenFileSlice(int FD, const char *Filename,
                                      std::unique_ptr<MemoryBuffer> &Result,
-                                     uint64_t MapSize, int64_t Offset);
+                                     uint64_t MapSize, int64_t Offset,
+                                     bool IsVolatile = false);
 
   /// Given an already-open file descriptor, read the file and return a
   /// MemoryBuffer.
+  ///
+  /// \param IsVolatile true indicates that the file may be changing often.
   static error_code getOpenFile(int FD, const char *Filename,
                                 OwningPtr<MemoryBuffer> &Result,
                                 uint64_t FileSize,
-                                bool RequiresNullTerminator = true);
+                                bool RequiresNullTerminator = true,
+                                bool IsVolatile = false);
   static error_code getOpenFile(int FD, const char *Filename,
                                 std::unique_ptr<MemoryBuffer> &Result,
                                 uint64_t FileSize,
-                                bool RequiresNullTerminator = true);
+                                bool RequiresNullTerminator = true,
+                                bool IsVolatile = false);
 
   /// getMemBuffer - Open the specified memory range as a MemoryBuffer.  Note
   /// that InputData must be null terminated if RequiresNullTerminator is true.
diff --git a/lib/Support/MemoryBuffer.cpp b/lib/Support/MemoryBuffer.cpp
index 773ccfd6f7..dc615d2a42 100644
--- a/lib/Support/MemoryBuffer.cpp
+++ b/lib/Support/MemoryBuffer.cpp
@@ -252,25 +252,29 @@ static error_code getMemoryBufferForStream(int FD,
 static error_code getFileAux(const char *Filename,
                              std::unique_ptr<MemoryBuffer> &Result,
                              int64_t FileSize,
-                             bool RequiresNullTerminator);
+                             bool RequiresNullTerminator,
+                             bool IsVolatile);
 
 error_code MemoryBuffer::getFile(Twine Filename,
                                  std::unique_ptr<MemoryBuffer> &Result,
                                  int64_t FileSize,
-                                 bool RequiresNullTerminator) {
+                                 bool RequiresNullTerminator,
+                                 bool IsVolatile) {
   // Ensure the path is null terminated.
   SmallString<256> PathBuf;
   StringRef NullTerminatedName = Filename.toNullTerminatedStringRef(PathBuf);
   return getFileAux(NullTerminatedName.data(), Result, FileSize,
-                    RequiresNullTerminator);
+                    RequiresNullTerminator, IsVolatile);
 }
 
 error_code MemoryBuffer::getFile(Twine Filename,
                                  OwningPtr<MemoryBuffer> &Result,
                                  int64_t FileSize,
-                                 bool RequiresNullTerminator) {
+                                 bool RequiresNullTerminator,
+                                 bool IsVolatile) {
   std::unique_ptr<MemoryBuffer> MB;
-  error_code ec = getFile(Filename, MB, FileSize, RequiresNullTerminator);
+  error_code ec = getFile(Filename, MB, FileSize, RequiresNullTerminator,
+                          IsVolatile);
   Result = std::move(MB);
   return ec;
 }
@@ -278,18 +282,20 @@ error_code MemoryBuffer::getFile(Twine Filename,
 static error_code getOpenFileImpl(int FD, const char *Filename,
                                   std::unique_ptr<MemoryBuffer> &Result,
                                   uint64_t FileSize, uint64_t MapSize,
-                                  int64_t Offset, bool RequiresNullTerminator);
+                                  int64_t Offset, bool RequiresNullTerminator,
+                                  bool IsVolatile);
 
 static error_code getFileAux(const char *Filename,
                              std::unique_ptr<MemoryBuffer> &Result, int64_t FileSize,
-                             bool RequiresNullTerminator) {
+                             bool RequiresNullTerminator,
+                             bool IsVolatile) {
   int FD;
   error_code EC = sys::fs::openFileForRead(Filename, FD);
   if (EC)
     return EC;
 
   error_code ret = getOpenFileImpl(FD, Filename, Result, FileSize, FileSize, 0,
-                                   RequiresNullTerminator);
+                                   RequiresNullTerminator, IsVolatile);
   close(FD);
   return ret;
 }
@@ -348,7 +354,8 @@ static bool shouldUseMmap(int FD,
 static error_code getOpenFileImpl(int FD, const char *Filename,
                                   std::unique_ptr<MemoryBuffer> &Result,
                                   uint64_t FileSize, uint64_t MapSize,
-                                  int64_t Offset, bool RequiresNullTerminator) {
+                                  int64_t Offset, bool RequiresNullTerminator,
+                                  bool IsVolatile) {
   static int PageSize = sys::process::get_self()->page_size();
 
   // Default is to map the full file.
@@ -374,7 +381,8 @@ static error_code getOpenFileImpl(int FD, const char *Filename,
     MapSize = FileSize;
   }
 
-  if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
+  if (!IsVolatile &&
+      shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
                     PageSize)) {
     error_code EC;
     Result.reset(new (NamedBufferAlloc(Filename)) MemoryBufferMMapFile(
@@ -428,33 +436,39 @@ static error_code getOpenFileImpl(int FD, const char *Filename,
 error_code MemoryBuffer::getOpenFile(int FD, const char *Filename,
                                      std::unique_ptr<MemoryBuffer> &Result,
                                      uint64_t FileSize,
-                                     bool RequiresNullTerminator) {
+                                     bool RequiresNullTerminator,
+                                     bool IsVolatile) {
   return getOpenFileImpl(FD, Filename, Result, FileSize, FileSize, 0,
-                         RequiresNullTerminator);
+                         RequiresNullTerminator, IsVolatile);
 }
 
 error_code MemoryBuffer::getOpenFile(int FD, const char *Filename,
                                      OwningPtr<MemoryBuffer> &Result,
                                      uint64_t FileSize,
-                                     bool RequiresNullTerminator) {
+                                     bool RequiresNullTerminator,
+                                     bool IsVolatile) {
   std::unique_ptr<MemoryBuffer> MB;
   error_code ec = getOpenFileImpl(FD, Filename, MB, FileSize, FileSize, 0,
-                                  RequiresNullTerminator);
+                                  RequiresNullTerminator, IsVolatile);
   Result = std::move(MB);
   return ec;
 }
 
 error_code MemoryBuffer::getOpenFileSlice(int FD, const char *Filename,
                                           std::unique_ptr<MemoryBuffer> &Result,
-                                          uint64_t MapSize, int64_t Offset) {
-  return getOpenFileImpl(FD, Filename, Result, -1, MapSize, Offset, false);
+                                          uint64_t MapSize, int64_t Offset,
+                                          bool IsVolatile) {
+  return getOpenFileImpl(FD, Filename, Result, -1, MapSize, Offset, false,
+                         IsVolatile);
 }
 
 error_code MemoryBuffer::getOpenFileSlice(int FD, const char *Filename,
                                           OwningPtr<MemoryBuffer> &Result,
-                                          uint64_t MapSize, int64_t Offset) {
+                                          uint64_t MapSize, int64_t Offset,
+                                          bool IsVolatile) {
   std::unique_ptr<MemoryBuffer> MB;
-  error_code ec = getOpenFileImpl(FD, Filename, MB, -1, MapSize, Offset, false);
+  error_code ec = getOpenFileImpl(FD, Filename, MB, -1, MapSize, Offset, false,
+                                  IsVolatile);
   Result = std::move(MB);
   return ec;
 }