1 // Copyright 2014 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 // This file provides a C++ wrapping around the Mojo C API for shared buffers,
6 // replacing the prefix of "Mojo" with a "mojo" namespace, and using more
7 // strongly-typed representations of |MojoHandle|s.
8 //
9 // Please see "mojo/public/c/system/buffer.h" for complete documentation of the
10 // API.
11 
12 #ifndef MOJO_PUBLIC_CPP_SYSTEM_BUFFER_H_
13 #define MOJO_PUBLIC_CPP_SYSTEM_BUFFER_H_
14 
15 #include <stdint.h>
16 
17 #include <memory>
18 
19 #include "base/compiler_specific.h"
20 #include "base/logging.h"
21 #include "mojo/public/c/system/buffer.h"
22 #include "mojo/public/cpp/system/handle.h"
23 
24 namespace mojo {
25 namespace internal {
26 
27 struct Unmapper {
operatorUnmapper28   void operator()(void* buffer) {
29     MojoResult result = MojoUnmapBuffer(buffer);
30     DCHECK_EQ(MOJO_RESULT_OK, result);
31   }
32 };
33 
34 }  // namespace internal
35 
36 using ScopedSharedBufferMapping = std::unique_ptr<void, internal::Unmapper>;
37 
38 class SharedBufferHandle;
39 
40 typedef ScopedHandleBase<SharedBufferHandle> ScopedSharedBufferHandle;
41 
42 // A strongly-typed representation of a |MojoHandle| referring to a shared
43 // buffer.
44 class SharedBufferHandle : public Handle {
45  public:
46   enum class AccessMode {
47     READ_WRITE,
48     READ_ONLY,
49   };
50 
SharedBufferHandle()51   SharedBufferHandle() {}
SharedBufferHandle(MojoHandle value)52   explicit SharedBufferHandle(MojoHandle value) : Handle(value) {}
53 
54   // Copying and assignment allowed.
55 
56   // Creates a new SharedBufferHandle. Returns an invalid handle on failure.
57   static ScopedSharedBufferHandle Create(uint64_t num_bytes);
58 
59   // Clones this shared buffer handle. If |access_mode| is READ_ONLY or this is
60   // a read-only handle, the new handle will be read-only. On failure, this will
61   // return an empty result.
62   ScopedSharedBufferHandle Clone(AccessMode = AccessMode::READ_WRITE) const;
63 
64   // Maps |size| bytes of this shared buffer. On failure, this will return a
65   // null mapping.
66   ScopedSharedBufferMapping Map(uint64_t size) const;
67 
68   // Maps |size| bytes of this shared buffer, starting |offset| bytes into the
69   // buffer. On failure, this will return a null mapping.
70   ScopedSharedBufferMapping MapAtOffset(uint64_t size, uint64_t offset) const;
71 };
72 
73 static_assert(sizeof(SharedBufferHandle) == sizeof(Handle),
74               "Bad size for C++ SharedBufferHandle");
75 static_assert(sizeof(ScopedSharedBufferHandle) == sizeof(SharedBufferHandle),
76               "Bad size for C++ ScopedSharedBufferHandle");
77 
78 }  // namespace mojo
79 
80 #endif  // MOJO_PUBLIC_CPP_SYSTEM_BUFFER_H_
81