gecko-dev/ipc/glue/SharedMemory.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef mozilla_ipc_SharedMemory_h
#define mozilla_ipc_SharedMemory_h

#include "nsDebug.h"
#include "nsISupportsImpl.h"  // NS_INLINE_DECL_REFCOUNTING
#include "mozilla/Attributes.h"

#include "base/process.h"
#include "chrome/common/ipc_message_utils.h"

//
// This is a low-level wrapper around platform shared memory.  Don't
// use it directly; use Shmem allocated through IPDL interfaces.
//
namespace {
enum Rights { RightsNone = 0, RightsRead = 1 << 0, RightsWrite = 1 << 1 };
}  // namespace

namespace mozilla {

namespace ipc {
class SharedMemory;
}  // namespace ipc

namespace ipc {

class SharedMemory {
 protected:
  virtual ~SharedMemory() {
    Unmapped();
    Destroyed();
  }

 public:
  enum OpenRights {
    RightsReadOnly = RightsRead,
    RightsReadWrite = RightsRead | RightsWrite,
  };

  size_t Size() const { return mMappedSize; }

  virtual void* memory() const = 0;

  virtual bool Create(size_t size) = 0;
  virtual bool Map(size_t nBytes, void* fixed_address = nullptr) = 0;
  virtual void Unmap() = 0;

  virtual void CloseHandle() = 0;

  virtual bool WriteHandle(IPC::MessageWriter* aWriter) = 0;
  virtual bool ReadHandle(IPC::MessageReader* aReader) = 0;

  void Protect(char* aAddr, size_t aSize, int aRights) {
    char* memStart = reinterpret_cast<char*>(memory());
    if (!memStart) MOZ_CRASH("SharedMemory region points at NULL!");
    char* memEnd = memStart + Size();

    char* protStart = aAddr;
    if (!protStart) MOZ_CRASH("trying to Protect() a NULL region!");
    char* protEnd = protStart + aSize;

    if (!(memStart <= protStart && protEnd <= memEnd))
      MOZ_CRASH("attempt to Protect() a region outside this SharedMemory");

    // checks alignment etc.
    SystemProtect(aAddr, aSize, aRights);
  }

  // bug 1168843, compositor thread may create shared memory instances that are
  // destroyed by main thread on shutdown, so this must use thread-safe RC to
  // avoid hitting assertion
  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedMemory)

  static void SystemProtect(char* aAddr, size_t aSize, int aRights);
  [[nodiscard]] static bool SystemProtectFallible(char* aAddr, size_t aSize,
                                                  int aRights);
  static size_t SystemPageSize();
  static size_t PageAlignedSize(size_t aSize);

 protected:
  SharedMemory();

  // Implementations should call these methods on shmem usage changes,
  // but *only if* the OS-specific calls are known to have succeeded.
  // The methods are expected to be called in the pattern
  //
  //   Created (Mapped Unmapped)* Destroy
  //
  // but this isn't checked.
  void Created(size_t aNBytes);
  void Mapped(size_t aNBytes);
  void Unmapped();
  void Destroyed();

  // The size of the shmem region requested in Create(), if
  // successful.  SharedMemory instances that are opened from a
  // foreign handle have an alloc size of 0, even though they have
  // access to the alloc-size information.
  size_t mAllocSize;
  // The size of the region mapped in Map(), if successful.  All
  // SharedMemorys that are mapped have a non-zero mapped size.
  size_t mMappedSize;
};

template <typename HandleImpl>
class SharedMemoryCommon : public SharedMemory {
 public:
  typedef HandleImpl Handle;

  virtual Handle CloneHandle() = 0;
  virtual bool IsHandleValid(const Handle& aHandle) const = 0;
  virtual bool SetHandle(Handle aHandle, OpenRights aRights) = 0;

  virtual bool WriteHandle(IPC::MessageWriter* aWriter) override {
    Handle handle = CloneHandle();
    if (!handle) {
      return false;
    }
    IPC::WriteParam(aWriter, std::move(handle));
    return true;
  }

  virtual bool ReadHandle(IPC::MessageReader* aReader) override {
    Handle handle;
    return IPC::ReadParam(aReader, &handle) && IsHandleValid(handle) &&
           SetHandle(std::move(handle), RightsReadWrite);
  }
};

}  // namespace ipc
}  // namespace mozilla

#endif  // ifndef mozilla_ipc_SharedMemory_h