[llvm] r325274 - Call FlushFileBuffers on output files.

[Zachary Turner via llvm-commits]

Author: zturner
Date: Thu Feb 15 10:36:10 2018
New Revision: 325274

URL: http://llvm.org/viewvc/llvm-project?rev=325274&view=rev
Log:
Call FlushFileBuffers on output files.

There is a latent Windows kernel bug, the exact trigger
conditions are not well understood, which can cause a file
to be correctly written, but unable to be correctly read.

The workaround appears to be simply calling FlushFileBuffers.

Differential Revision: https://reviews.llvm.org/D42925

Modified:
    llvm/trunk/include/llvm/Support/FileSystem.h
    llvm/trunk/lib/Support/Windows/Path.inc

Modified: llvm/trunk/include/llvm/Support/FileSystem.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/FileSystem.h?rev=325274&r1=325273&r2=325274&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/FileSystem.h (original)
+++ llvm/trunk/include/llvm/Support/FileSystem.h Thu Feb 15 10:36:10 2018
@@ -819,6 +819,8 @@ private:
   /// Platform-specific mapping state.
   size_t Size;
   void *Mapping;
+  int FD;
+  mapmode Mode;
 
   std::error_code init(int FD, uint64_t Offset, mapmode Mode);
 

Modified: llvm/trunk/lib/Support/Windows/Path.inc
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Support/Windows/Path.inc?rev=325274&r1=325273&r2=325274&view=diff
==============================================================================
--- llvm/trunk/lib/Support/Windows/Path.inc (original)
+++ llvm/trunk/lib/Support/Windows/Path.inc Thu Feb 15 10:36:10 2018
@@ -822,6 +822,8 @@ std::error_code setLastModificationAndAc
 
 std::error_code mapped_file_region::init(int FD, uint64_t Offset,
                                          mapmode Mode) {
+  this->FD = FD;
+  this->Mode = Mode;
   HANDLE FileHandle = reinterpret_cast<HANDLE>(_get_osfhandle(FD));
   if (FileHandle == INVALID_HANDLE_VALUE)
     return make_error_code(errc::bad_file_descriptor);
@@ -887,8 +889,20 @@ mapped_file_region::mapped_file_region(i
 }
 
 mapped_file_region::~mapped_file_region() {
-  if (Mapping)
+  if (Mapping) {
     ::UnmapViewOfFile(Mapping);
+
+    if (Mode == mapmode::readwrite) {
+      // There is a Windows kernel bug, the exact trigger conditions of which
+      // are not well understood.  When triggered, dirty pages are not properly
+      // flushed and subsequent process's attempts to read a file can return
+      // invalid data.  Calling FlushFileBuffers on the write handle is
+      // sufficient to ensure that this bug is not triggered.
+      HANDLE FileHandle = reinterpret_cast<HANDLE>(_get_osfhandle(FD));
+      if (FileHandle != INVALID_HANDLE_VALUE)
+        ::FlushFileBuffers(FileHandle);
+    }
+  }
 }
 
 size_t mapped_file_region::size() const {