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Modern Operating Systems by Herbert Bos and Andrew S. Tanenb...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf
Showing 904 out of 1137
Modern Operating Systems by Herbert Bos and Andrew...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Modern Operating Systems by Herbert...
Modern_Operating_Systems_by_Herbert_Bos_and_Andrew_S._Tanenbaum_4th_Ed.pdf-M ODERN O PERATING S YSTEMS
Page 904
SEC. 11.2
PROGRAMMING WINDOWS
873
Win32 has calls for creating and managing both processes and threads.
There
are also many calls that relate to interprocess communication, such as creating, de-
stroying, and using mutexes, semaphores, events, communication ports, and other
IPC objects.
Although much of the memory-management system is invisible to pro-
grammers, one important feature is visible: namely the ability of a process to map
a file onto a region of its virtual memory.
This allows threads running in a process
the ability to read and write parts of the file using pointers without having to expli-
citly perform read and write operations to transfer data between the disk and mem-
ory.
With memory-mapped files the memory-management system itself performs
the I/Os as needed (demand paging).
Windows implements memory-mapped files using three completely different
facilities. First it provides interfaces which allow processes to manage their own
virtual address space, including reserving ranges of addresses for later use.
Sec-
ond, Win32 supports an abstraction called a
file mapping
, which is used to repres-
ent addressable objects like files (a file mapping is called a
section
in the NT
layer). Most often, file mappings are created to refer to files using a file handle,
but they can also be created to refer to private pages allocated from the system
pagefile.
The third facility maps
views
of file mappings into a process’ address space.
Win32 allows only
a view to be created for the current process, but the underlying
NT facility is more general, allowing views to be created for any process for which
you have a handle with the appropriate permissions.
Separating the creation of a
file mapping from the operation of mapping the file into the address space is a dif-
ferent approach than used in the
mmap
function in UNIX.
In Windows, the file mappings are kernel-mode objects represented by a hand-
le. Like most handles, file mappings can be duplicated into other processes.
Each
of these processes can map the file mapping into its own address space as it sees
fit. This is useful for sharing private memory between processes without having to
create files for sharing.
At the NT layer, file mappings (sections) can also be made
persistent in the NT namespace and accessed by name.
An important area for many programs is file I/O.
In the basic Win32 view, a
file is just a linear sequence of bytes.
Win32 provides over 60 calls for creating
and destroying files and directories, opening and closing files, reading and writing
them, requesting and setting file attributes, locking ranges of bytes, and many more
fundamental operations on both the organization of the file system and access to
individual files.
There are also various advanced facilities for managing data in files. In addi-
tion to the primary data stream, files stored on the NTFS file system can have addi-
tional data streams.
Files (and even entire volumes) can be encrypted.
Files can be
compressed, and/or represented as a sparse stream of bytes where missing regions
of data in the middle occupy no storage on disk.
File-system volumes can be
organized out of multiple separate disk partitions using different levels of RAID
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