Introduce base::ScopedPlatformHandle

base/files/scoped_platform_handle.h

Index: base/files/scoped_platform_handle.h
diff --git a/base/files/scoped_platform_handle.h b/base/files/scoped_platform_handle.h
new file mode 100644
index 0000000000000000000000000000000000000000..c5f5ee2c26b9da89e19487789334e804077b8158
--- /dev/null
+++ b/base/files/scoped_platform_handle.h
@@ -0,0 +1,164 @@
+// Copyright 2017 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.
+
+#ifndef BASE_FILES_SCOPED_PLATFORM_HANDLE_H_
+#define BASE_FILES_SCOPED_PLATFORM_HANDLE_H_
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include "base/base_export.h"
+#include "build/build_config.h"
+
+#if defined(OS_WIN)
+#include <windows.h>
+
+#include "base/win/scoped_handle.h"
+#elif defined(OS_POSIX)
+#include "base/files/scoped_file.h"
+#endif
+
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+#include <mach/mach.h>
+
+#include "base/mac/scoped_mach_port.h"
+#endif
+
+namespace base {
+
+// A ScopedPlatformHandle encapsulates ownership of one of various types of
+// platform-specific resource handles including POSIX file descriptors, Windows
+// handles, and Mach ports.
+//
+// The purpose of this type is to have a consistent representation of such
+// resources for the sake of safe ownership semantics, relegating
+// platform-specific details to either the code which initially acquires the
+// resource or the code which actually uses it.
+class BASE_EXPORT ScopedPlatformHandle {
+ public:
+  // The underlying type of the ScopedPlatformHandle. Note that the possible
+  // values for this type are platform-dependent.
+  enum class Type {
+    INVALID,
+#if defined(OS_WIN)
+    WINDOWS_HANDLE,
+#elif defined(OS_POSIX)
+    FILE_DESCRIPTOR,
+#endif
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+    MACH_PORT_SEND,
+    MACH_PORT_RECEIVE,
+#endif
+  };
+
+  // Constructors for an invalid ScopedPlatformHandle of type |Type::INVALID|.
+  ScopedPlatformHandle();
+  ScopedPlatformHandle(std::nullptr_t);
+
+  ScopedPlatformHandle(ScopedPlatformHandle&& other);
+
+#if defined(OS_WIN)
+  // Constructors which take ownership of a Windows handle.
+  explicit ScopedPlatformHandle(HANDLE handle);
+  explicit ScopedPlatformHandle(win::ScopedHandle handle)
+#elif defined(OS_POSIX)
+  // Constructors which take ownership of a POSIX file descriptor.
+  explicit ScopedPlatformHandle(int fd);
+  explicit ScopedPlatformHandle(ScopedFD fd);
+#endif  // defined(OS_WIN)
+
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  // Constructors which take ownership of Mach port rights. The raw
+  // |mach_port_t| version implies a send right.
+  explicit ScopedPlatformHandle(mach_port_t port);
+  explicit ScopedPlatformHandle(mac::ScopedMachSendRight port);
+  explicit ScopedPlatformHandle(mac::ScopedMachReceiveRight port);
+#endif
+
+  ~ScopedPlatformHandle();
+
+  ScopedPlatformHandle& operator=(ScopedPlatformHandle&& other);
+
+  Type type() const { return type_; }
+
+  // Indicates whether this ScopedPlatformHandle is valid. In order for a
+  // ScopedPlatformHandle to be valid, its type must be something other than
+  // |Type::INVALID|, and its value must reflect a valid value for that specific
+  // type of handle.
+  bool is_valid() const;
+
+  // Closes the handle and resets the type to |Type::INVALID|.
+  void reset();
+
+#if defined(OS_WIN)
+  // If this ScopedPlatformHandle is of type |Type::WINDOWS_HANDLE|, this
+  // returns |true| and populates |*handle| with its value. Otherwise returns
+  // |false|.
+  bool GetAsWindowsHandle(HANDLE* handle) const;
+
+  // Like GetAsWindowsHandle() above, but tranfers ownership. The
+  // ScopedPlatformHandle is always reset to |Type::INVALID| after this call.
+  bool TakeWindowsHandle(win::ScopedHandle* handle);
+
+  // Like above, but transfers ownership to an unsafe unscoped type.
+  bool ReleaseAsWindowsHandle(HANDLE* handle);
+#elif defined(OS_POSIX)
+  // If this ScopedPlatformHandle is of type |Type::FILE_DESCRIPTOR|, this
+  // returns |true| and populates |*fd| with its value. Otherwise returns
+  // |false|.
+  bool GetAsFileDescriptor(int* fd) const;
+
+  // Like GetAsFileDescriptor() above, but transfers ownership. The
+  // ScopedPlatformHandle is always reset to |Type::INVALID| after this call.
+  bool TakeFileDescriptor(ScopedFD* fd);
+
+  // Like above, but transfers ownership to an unsafe unscoped type.
+  bool ReleaseAsFileDescriptor(int* fd);
+#endif
+
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  // If this ScopedPlatformHandle is of type |Type::MACH_PORT_SEND| or
+  // |Type::MACH_PORT_RECEIVE|, this returns |true| and populates |*port| with
+  // its value. Otherwise returns |false|.
+  bool GetAsMachPort(mach_port_t* port) const;
+
+  // If this ScopedPlatformHandle is of type |Type::MACH_PORT_SEND| this returns
+  // |true| and populates |*port| with its value. Otherwise returns |false|. The
+  // ScopedPlatformHandle is always reset to |Type::INVALID| after this call.
+  bool TakeMachPortSendRight(mac::ScopedMachSendRight* port);
+
+  // If this ScopedPlatformHandle is of type |Type::MACH_PORT_RECEIVE| this
+  // returns |true| and populates |*port| with its value. Otherwise returns
+  // |false|. The ScopedPlatformHandle is always reset to |Type::INVALID| after
+  // this call.
+  bool TakeMachPortReceiveRight(mac::ScopedMachReceiveRight* port);
+
+  // Like GetAsMachPort above, but transfers ownership to the unsafe, unscoped
+  // |*port|.
+  bool ReleaseAsMachPort(mach_port_t* port);
+#endif  // defined(OS_MACOSX) && !defined(OS_IOS)
+
+ private:
+  Type type_;
+
+  // NOTE: At most one of the fields below may be used at any given time, and
+  // the one in use depends on the value of |type_|. We avoid using unified
+  // storage here in order to leverage the existing scoping behavior of the
+  // individual platform handle types.

[dcheng, 2017/02/18 00:14:03]

A C++11 union should still allow the existing scoping behavior to just work,
right? And it'll make the handle size smaller on Mac.

+
+#if defined(OS_WIN)
+  win::ScopedHandle windows_handle_;
+#elif defined(OS_POSIX)
+  ScopedFD file_descriptor_;
+#endif
+
+#if defined(OS_MACOSX) && !defined(OS_IOS)
+  mac::ScopedMachSendRight mach_port_send_;
+  mac::ScopedMachReceiveRight mach_port_receive_;
+#endif
+};
+
+}  // namespace base
+
+#endif  // BASE_FILES_SCOPED_PLATFORM_HANDLE_H_