共享一个之前封装的多进程共享内存的MemoryStream

</pre><pre class="html" name="code">{共享内存封装.封装成了MemoryStream的形式.用法如下:  var    ms : TShareMemStream;  ms := TShareMemStream.Create('Global\test', FILE_MAP_ALL_ACCESS, 4096);  if (ms.Memory <> nil)(*and(ms.AlreadyExists)*) then  //如果创建失败Memory指针是空指针  //AlreadyExists表示已经存在了,也就是之前被别人(也许是别的进程)创建过了.  begin    //获取锁,多个进程线程访问安全访问    if ms.GetLock(INFINITE) then    begin      ms.read(...);      ms.write(...);      //释放锁      ms.ReleaseLock();    end;  end;  ms.free;}unit ShareMemoryStream; interface uses  SysUtils, Classes, Syncobjs,  Windows; type  TShareMemStream = class(TCustomMemoryStream)  private    FFile: THandle;    FSize: Int64;    FEvent: TEvent;    FAlreadyExists: Boolean;  protected    property Event: TEvent read FEvent;  public    constructor Create(const ShareName: string;      ACCESS: DWORD = FILE_MAP_ALL_ACCESS; ASize: Int64 = 16 * 1024 * 1024);    destructor Destroy; override;     function Write(const Buffer; Count: Integer): Longint; override;     function GetLock(ATimeOut: DWORD = INFINITE): Boolean;    procedure ReleaseLock();     property AlreadyExists: Boolean read FAlreadyExists;  end; implementation procedure InitSecAttr(var sa: TSecurityAttributes; var sd: TSecurityDescriptor);begin  sa.nLength := sizeOf(sa);  sa.lpSecurityDescriptor := @sd;  sa.bInheritHandle := false;  InitializeSecurityDescriptor(@sd, SECURITY_DESCRIPTOR_REVISION);  SetSecurityDescriptorDacl(@sd, true, nil, false);end; { TShareMem } constructor TShareMemStream.Create(const ShareName: string; ACCESS: DWORD;  ASize: Int64);var  sa: TSecurityAttributes;  sd: TSecurityDescriptor;  lprotect: DWORD;  e: Integer;begin  FEvent := TEvent.Create(nil, false, true, ShareName +    '_TShareMemStream_Event');  FSize := ASize;  InitSecAttr(sa, sd);   ACCESS := ACCESS and (not SECTION_MAP_EXECUTE);   if (ACCESS and FILE_MAP_WRITE) = FILE_MAP_WRITE then    lprotect := PAGE_READWRITE  else if (ACCESS and FILE_MAP_READ) = FILE_MAP_READ then    lprotect := PAGE_READONLY;   FFile := CreateFileMapping(INVALID_HANDLE_VALUE, @sa, lprotect,    Int64Rec(FSize).Hi, Int64Rec(FSize).Lo, PChar(ShareName));  e := GetLastError;  if FFile = 0 then    Exit;  FAlreadyExists := e = ERROR_ALREADY_EXISTS;  SetPointer(MapViewOfFile(FFile, ACCESS, 0, 0, Int64Rec(FSize).Lo),    Int64Rec(FSize).Lo);end; destructor TShareMemStream.Destroy;begin  if Memory <> nil then  begin    UnmapViewOfFile(Memory);    SetPointer(nil, 0);    Position := 0;  end;  if FFile <> 0 then  begin    CloseHandle(FFile);    FFile := 0;  end;  FEvent.Free;  inherited Destroy;end; function TShareMemStream.GetLock(ATimeOut: DWORD): Boolean;var  wr : TWaitResult;begin  wr := FEvent.WaitFor(ATimeOut);  Result := wr = wrSignaled;end; procedure TShareMemStream.ReleaseLock;begin  FEvent.SetEvent;end; function TShareMemStream.Write(const Buffer; Count: Integer): Longint;begin  Result := 0;  if (Size - Position) >= Count then  begin    System.Move(Buffer, PByte(Memory)[Position], Count);    Position := Position + Count;    Result := Count;  end;end; end.