// 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.
#ifndef MOJO_SYSTEM_RAW_SHARED_BUFFER_H_
#define MOJO_SYSTEM_RAW_SHARED_BUFFER_H_
#include <stddef.h>
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/memory/scoped_ptr.h"
#include "base/synchronization/lock.h"
#include "mojo/embedder/scoped_platform_handle.h"
#include "mojo/system/system_impl_export.h"
namespace mojo {
namespace system {
class RawSharedBufferMapping;
// |RawSharedBuffer| is a thread-safe, ref-counted wrapper around OS-specific
// shared memory. It has the following features:
// - A |RawSharedBuffer| simply represents a piece of shared memory that *may*
// be mapped and *may* be shared to another process.
// - A single |RawSharedBuffer| may be mapped multiple times. The lifetime of
// the mapping (owned by |RawSharedBufferMapping|) is separate from the
// lifetime of the |RawSharedBuffer|.
// - Sizes/offsets (of the shared memory and mappings) are arbitrary, and not
// restricted by page size. However, more memory may actually be mapped than
// requested.
//
// It currently does NOT support the following:
// - Sharing read-only. (This will probably eventually be supported.)
//
// TODO(vtl): Rectify this with |base::SharedMemory|.
class MOJO_SYSTEM_IMPL_EXPORT RawSharedBuffer
: public base::RefCountedThreadSafe<RawSharedBuffer> {
public:
// Creates a shared buffer of size |num_bytes| bytes (initially zero-filled).
// |num_bytes| must be nonzero. Returns null on failure.
static RawSharedBuffer* Create(size_t num_bytes);
// Maps (some) of the shared buffer into memory; [|offset|, |offset + length|]
// must be contained in [0, |num_bytes|], and |length| must be at least 1.
// Returns null on failure.
scoped_ptr<RawSharedBufferMapping> Map(size_t offset, size_t length);
// Checks if |offset| and |length| are valid arguments.
bool IsValidMap(size_t offset, size_t length);
// Like |Map()|, but doesn't check its arguments (which should have been
// preflighted using |IsValidMap()|).
scoped_ptr<RawSharedBufferMapping> MapNoCheck(size_t offset, size_t length);
size_t num_bytes() const { return num_bytes_; }
private:
friend class base::RefCountedThreadSafe<RawSharedBuffer>;
explicit RawSharedBuffer(size_t num_bytes);
~RawSharedBuffer();
// This is called by |Create()| before this object is given to anyone (hence
// it doesn't need to take |lock_|).
bool InitNoLock();
// The platform-dependent part of |Map()|; doesn't check arguments. Called
// under |lock_|.
scoped_ptr<RawSharedBufferMapping> MapImplNoLock(size_t offset,
size_t length);
const size_t num_bytes_;
base::Lock lock_; // Protects |handle_|.
embedder::ScopedPlatformHandle handle_;
DISALLOW_COPY_AND_ASSIGN(RawSharedBuffer);
};
// A mapping of a |RawSharedBuffer| (compararable to a "file view" in Windows);
// see above. Created by |RawSharedBuffer::Map()|. Automatically unmaps memory
// on destruction.
//
// Mappings are NOT thread-safe.
//
// Note: This is an entirely separate class (instead of
// |RawSharedBuffer::Mapping|) so that it can be forward-declared.
class MOJO_SYSTEM_IMPL_EXPORT RawSharedBufferMapping {
public:
~RawSharedBufferMapping() { Unmap(); }
void* base() const { return base_; }
size_t length() const { return length_; }
private:
friend class RawSharedBuffer;
RawSharedBufferMapping(void* base,
size_t length,
void* real_base,
size_t real_length)
: base_(base), length_(length),
real_base_(real_base), real_length_(real_length) {}
void Unmap();
void* const base_;
const size_t length_;
void* const real_base_;
const size_t real_length_;
DISALLOW_COPY_AND_ASSIGN(RawSharedBufferMapping);
};
} // namespace system
} // namespace mojo
#endif // MOJO_SYSTEM_RAW_SHARED_BUFFER_H_