Make an RAII initializer for COM on Windows

[zturner]

Summary

Patch should be fairly self-explanatory. Implementation is empty on non-Windows platforms, and on Windows platforms simply calls CoInitializeEx and CoUninitialize.

[majnemer]

Might be nice to have 'RAII' in the class name.

[zturner]

In D9267#161494, @majnemer wrote:

Might be nice to have 'RAII' in the class name.

Do we do that for any other types of these classes? For example, there's llvm_shutdown_obj, scoped_ptr? I don't feel too strongly either way, but if this is a desirable naming convention then we shoudl think about formalizing it.

[majnemer]

In D9267#161495, @zturner wrote:

In D9267#161494, @majnemer wrote:

Might be nice to have 'RAII' in the class name.

Do we do that for any other types of these classes? For example, there's llvm_shutdown_obj, scoped_ptr? I don't feel too strongly either way, but if this is a desirable naming convention then we shoudl think about formalizing it.

Sure: NewQueueRAII, TemplateParameterDepthRAII, ContextRAII, FPContractStateRAII, CompoundScopeRAII, CXXThisScopeRAII, ArgumentPackSubstitutionIndexRAII, etc.

include/llvm/Support/COM.h

+//===- llvm/Support/COM.h ---------------------------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+/// \file
+///
+/// Provides a library for accessing COM functionality of the Host OS.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_COM_H
+#define LLVM_SUPPORT_COM_H
+
+namespace llvm {
+namespace sys {
+
+enum class COMThreadingMode { ApartmentThreaded, FreeThreaded };
+
+class COMInitializer {
+public:
+  COMInitializer(COMThreadingMode Threading, bool SpeedOverMemory = false);
+  ~COMInitializer();
+
+private:
+  COMInitializer(const COMInitializer &) = delete;
+  void operator=(const COMInitializer &) = delete;
+};
+}
+}
+
+#endif

lib/Support/CMakeLists.txt

   BlockFrequency.cpp
   BranchProbability.cpp
   circular_raw_ostream.cpp
+  COM.cpp
   CommandLine.cpp
   Compression.cpp
   ConvertUTF.c

lib/Support/COM.cpp

+//===-- COM.cpp - Implement COM utility classes -----------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements utility classes related to COM.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/COM.h"
+
+#include "llvm/Config/config.h"
+
+// Include the platform-specific parts of this class.
+#ifdef LLVM_ON_UNIX
+#include "Unix/COM.inc"
+#endif
+#ifdef LLVM_ON_WIN32
+#include "Windows/COM.inc"
+#endif

lib/Support/Unix/COM.inc

+//===- llvm/Support/Unix/COM.inc - Unix COM Implementation -----*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Unix portion of COM support.
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only generic UNIX code that
+//===          is guaranteed to work on *all* UNIX variants.
+//===----------------------------------------------------------------------===//
+
+namespace llvm {
+namespace sys {
+
+COMInitializer::COMInitializer(COMThreadingMode Threading,
+                               bool SpeedOverMemory) {}
+
+COMInitializer::~COMInitializer() {}
+}
+}

lib/Support/Windows/COM.inc

+//===- llvm/Support/Windows/COM.inc - Windows COM Implementation *- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Windows portion of COM support.
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only generic UNIX code that
+//===          is guaranteed to work on *all* UNIX variants.
+//===----------------------------------------------------------------------===//
+
+// We need to #include <windows.h> directly, and not WindowsSupport.h, because
+// WindowsSupport.h #defines WIN32_LEAN_AND_MEAN, which will prevent COM headers
+// from getting included.
+#include <windows.h>
+
+namespace llvm {
+namespace sys {
+
+COMInitializer::COMInitializer(COMThreadingMode Threading,
+                               bool SpeedOverMemory) {
+  DWORD Coinit = 0;
+  if (Threading == COMThreadingMode::ApartmentThreaded)
+    Coinit |= COINIT_APARTMENTTHREADED;
+  else
+    Coinit |= COINIT_MULTITHREADED;
+  if (SpeedOverMemory)
+    Coinit |= COINIT_SPEED_OVER_MEMORY;
+  ::CoInitializeEx(nullptr, Coinit);
+}
+
+COMInitializer::~COMInitializer() { ::CoUninitialize(); }
+}
+}