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Modern Operating Systems by Herbert Bos and Andrew...
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Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
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CHAP. 11
Apart from the object-type callbacks, the object manager also provides a set of
generic object routines for operations like creating objects and object types, dupli-
cating handles, getting a referenced pointer from a handle or name, adding and
subtracting reference counts to the object header, and
(the generic function
that closes all types of handles).
Although the object namespace is crucial to the entire operation of the system,
few people know that it even exists because it is not visible to users without special
viewing tools.
One such viewing tool is
, available for free at the URL
When run, this tool depicts an object
namespace that typically contains the object directories listed in Fig. 11-19 as well
as a few others.
Starting place for looking up MS-DOS devices like C:
\ DosDevices
Official name of \ ??, but really just a symbolic link to \ ??
All discovered I/O devices
Objects corresponding to each loaded device driver
The type objects such as those listed in Fig. 11-21
Objects for sending messages to all the Win32 GUI windows
User-created Win32 objects such as semaphores, mutexes, etc.
Partition names discovered by the boot loader
National Language Support objects
File-system driver objects and file system recognizer objects
Objects belonging to the security system
Key shared libraries that are opened early and held open
Figure 11-19.
Some typical directories in the object namespace.
The strangely named directory
\ ??
contains the names of all the MS-DOS-
style device names, such as
: for the floppy disk and
: for the first hard disk.
These names are actually symbolic links to the directory
\ Device
where the device
objects live.
The name
\ ??
was chosen to make it alphabetically first so as to
speed up lookup of all path names beginning with a drive letter.
The contents of
the other object directories should be self explanatory.
As described above, the object manager keeps a separate handle count in every
object. This count is never larger than the referenced pointer count because each
valid handle has a referenced pointer to the object in its handle-table entry.
reason for the separate handle count is that many types of objects may need to have
their state cleaned up when the last user-mode reference disappears, even though
they are not yet ready to have their memory deleted.
One example is file objects, which represent an instance of an opened file. In
Windows, files can be opened for exclusive access. When the last handle for a file

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