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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
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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 940
SEC. 11.4
PROCESSES AND THREADS IN WINDOWS
909
but code that relies on these fields must query them often just to see if they have
changed. As with many performance hacks, it is a bit ugly, but it works.
Processes
Processes are created from section objects, each of which describes a memory
object backed by a file on disk.
When a process is created, the creating process re-
ceives a handle that allows it to modify the new process by mapping sections, allo-
cating virtual memory, writing parameters and environmental data, duplicating file
descriptors into its handle table, and creating threads.
This is very different than
how processes are created in UNIX and reflects the difference in the target systems
for the original designs of UNIX vs. Windows.
As described in Sec. 11.1, UNIX was designed for 16-bit single-processor sys-
tems that used swapping to share memory among processes.
In such systems, hav-
ing the process as the unit of concurrency and using an operation like
fork
to create
processes was a brilliant idea.
To run a new process with small memory and no
virtual memory hardware, processes in memory have to be swapped out to disk to
create space.
UNIX originally implemented
fork
simply by swapping out the par-
ent process and handing its physical memory to the child.
The operation was al-
most free.
In contrast, the hardware environment at the time Cutler’s team wrote NT was
32-bit multiprocessor systems with virtual memory hardware to share 1–16 MB of
physical memory.
Multiprocessors provide the opportunity to run parts of pro-
grams concurrently, so NT used processes as containers for sharing memory and
object resources, and used threads as the unit of concurrency for scheduling.
Of course, the systems of the next few years will look nothing like either of
these target environments, having 64-bit address spaces with dozens (or hundreds)
of CPU cores per chip socket and dozens or hundreds gigabytes of physical memo-
ry.
This memory may be radically different from current RAM as well.
Current
RAM loses its contents when powered off, but
phase-change memories
now in
the pipeline keep their values (like disks) even when powered off. Also expect
flash devices
to replace hard disks, broader support for virtualization, ubiquitous
networking, and support for synchronization innovations like
transactional mem-
ory
.
Windows and UNIX will continue to be adapted to new hardware realities,
but what will be really interesting is to see what new operating systems are de-
signed specifically for systems based on these advances.
Jobs and Fibers
Windows can group processes together into jobs.
Jobs group processes in
order to apply constraints to them and the threads they contain, such as limiting re-
source use via a shared quota or enforcing a
restricted token
that prevents threads
from accessing many system objects.
The most significant property of jobs for
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