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// Copyright 2014 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.
#include <stdint.h>
#include <limits>
#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/macros.h"
#include "mojo/public/c/system/functions.h"
#include "mojo/public/c/system/types.h"
#include "mojo/public/cpp/system/handle_signals_state.h"
namespace mojo {
// |Handle| and |...Handle|:
// |Handle| is a simple, copyable wrapper for the C type |MojoHandle| (which is
// just an integer). Its purpose is to increase type-safety, not provide
// lifetime management. For the same purpose, we have trivial *subclasses* of
// |Handle|, e.g., |MessagePipeHandle| and |DataPipeProducerHandle|. |Handle|
// and its subclasses impose *no* extra overhead over using |MojoHandle|s
// directly.
// Note that though we provide constructors for |Handle|/|...Handle| from a
// |MojoHandle|, we do not provide, e.g., a constructor for |MessagePipeHandle|
// from a |Handle|. This is for type safety: If we did, you'd then be able to
// construct a |MessagePipeHandle| from, e.g., a |DataPipeProducerHandle| (since
// it's a |Handle|).
// |ScopedHandleBase| and |Scoped...Handle|:
// |ScopedHandleBase<HandleType>| is a templated scoped wrapper, for the handle
// types above (in the same sense that a C++11 |unique_ptr<T>| is a scoped
// wrapper for a |T*|). It provides lifetime management, closing its owned
// handle on destruction. It also provides move semantics, again along the lines
// of C++11's |unique_ptr|. A moved-from |ScopedHandleBase<HandleType>| sets its
// handle value to MOJO_HANDLE_INVALID.
// |ScopedHandle| is just (a typedef of) a |ScopedHandleBase<Handle>|.
// Similarly, |ScopedMessagePipeHandle| is just a
// |ScopedHandleBase<MessagePipeHandle>|. Etc. Note that a
// |ScopedMessagePipeHandle| is *not* a (subclass of) |ScopedHandle|.
// Wrapper functions:
// We provide simple wrappers for the |Mojo...()| functions (in
// mojo/public/c/system/core.h -- see that file for details on individual
// functions).
// The general guideline is functions that imply ownership transfer of a handle
// should take (or produce) an appropriate |Scoped...Handle|, while those that
// don't take a |...Handle|. For example, |CreateMessagePipe()| has two
// |ScopedMessagePipe| "out" parameters, whereas |Wait()| and |WaitMany()| take
// |Handle| parameters. Some, have both: e.g., |DuplicatedBuffer()| takes a
// suitable (unscoped) handle (e.g., |SharedBufferHandle|) "in" parameter and
// produces a suitable scoped handle (e.g., |ScopedSharedBufferHandle| a.k.a.
// |ScopedHandleBase<SharedBufferHandle>|) as an "out" parameter.
// An exception are some of the |...Raw()| functions. E.g., |CloseRaw()| takes a
// |Handle|, leaving the user to discard the wrapper.
// ScopedHandleBase ------------------------------------------------------------
// Scoper for the actual handle types defined further below. It's move-only,
// like the C++11 |unique_ptr|.
template <class HandleType>
class ScopedHandleBase {
using RawHandleType = HandleType;
ScopedHandleBase() {}
explicit ScopedHandleBase(HandleType handle) : handle_(handle) {}
~ScopedHandleBase() { CloseIfNecessary(); }
template <class CompatibleHandleType>
explicit ScopedHandleBase(ScopedHandleBase<CompatibleHandleType> other)
: handle_(other.release()) {}
// Move-only constructor and operator=.
ScopedHandleBase(ScopedHandleBase&& other) : handle_(other.release()) {}
ScopedHandleBase& operator=(ScopedHandleBase&& other) {
if (&other != this) {
handle_ = other.release();
return *this;
const HandleType& get() const { return handle_; }
const HandleType* operator->() const { return &handle_; }
template <typename PassedHandleType>
static ScopedHandleBase<HandleType> From(
ScopedHandleBase<PassedHandleType> other) {
"HandleType is not a subtype of PassedHandleType");
return ScopedHandleBase<HandleType>(
void swap(ScopedHandleBase& other) { handle_.swap(other.handle_); }
HandleType release() WARN_UNUSED_RESULT {
HandleType rv;
return rv;
void reset(HandleType handle = HandleType()) {
handle_ = handle;
bool is_valid() const { return handle_.is_valid(); }
bool operator==(const ScopedHandleBase& other) const {
return handle_.value() == other.get().value();
void CloseIfNecessary() {
if (handle_.is_valid())
HandleType handle_;
template <typename HandleType>
inline ScopedHandleBase<HandleType> MakeScopedHandle(HandleType handle) {
return ScopedHandleBase<HandleType>(handle);
// Handle ----------------------------------------------------------------------
const MojoHandle kInvalidHandleValue = MOJO_HANDLE_INVALID;
// Wrapper base class for |MojoHandle|.
class Handle {
Handle() : value_(kInvalidHandleValue) {}
explicit Handle(MojoHandle value) : value_(value) {}
~Handle() {}
void swap(Handle& other) {
MojoHandle temp = value_;
value_ = other.value_;
other.value_ = temp;
bool is_valid() const { return value_ != kInvalidHandleValue; }
const MojoHandle& value() const { return value_; }
MojoHandle* mutable_value() { return &value_; }
void set_value(MojoHandle value) { value_ = value; }
void Close() {
MojoResult result = MojoClose(value_);
HandleSignalsState QuerySignalsState() const {
HandleSignalsState signals_state;
MojoResult result = MojoQueryHandleSignalsState(
value_, static_cast<MojoHandleSignalsState*>(&signals_state));
return signals_state;
MojoHandle value_;
// Copying and assignment allowed.
// Should have zero overhead.
static_assert(sizeof(Handle) == sizeof(MojoHandle), "Bad size for C++ Handle");
// The scoper should also impose no more overhead.
typedef ScopedHandleBase<Handle> ScopedHandle;
static_assert(sizeof(ScopedHandle) == sizeof(Handle),
"Bad size for C++ ScopedHandle");
// |Close()| takes ownership of the handle, since it'll invalidate it.
// Note: There's nothing to do, since the argument will be destroyed when it
// goes out of scope.
template <class HandleType>
inline void Close(ScopedHandleBase<HandleType> /*handle*/) {
// Most users should typically use |Close()| (above) instead.
inline MojoResult CloseRaw(Handle handle) {
return MojoClose(handle.value());
// Strict weak ordering, so that |Handle|s can be used as keys in |std::map|s,
inline bool operator<(const Handle a, const Handle b) {
return a.value() < b.value();
// Comparison, so that |Handle|s can be used as keys in hash maps.
inline bool operator==(const Handle a, const Handle b) {
return a.value() == b.value();
} // namespace mojo