gecko-dev/ipc/glue/SharedMemory.h

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#ifndef mozilla_ipc_SharedMemory_h
#define mozilla_ipc_SharedMemory_h

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

//
// 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 mozilla {
namespace ipc {

class SharedMemory
{
public:
  enum SharedMemoryType {
    TYPE_BASIC,
    TYPE_SYSV,
    TYPE_UNKNOWN
  };

  virtual ~SharedMemory() { Unmapped(); Destroyed(); }

  size_t Size() const { return mMappedSize; }

  virtual void* memory() const = 0;

  virtual bool Create(size_t size) = 0;
  virtual bool Map(size_t nBytes) = 0;

  virtual SharedMemoryType Type() const = 0;

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

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

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

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

  NS_INLINE_DECL_REFCOUNTING(SharedMemory)

  static void SystemProtect(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;
};

} // namespace ipc
} // namespace mozilla


#endif // ifndef mozilla_ipc_SharedMemory_h