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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 897
866
CASE STUDY 2: WINDOWS 8
CHAP. 11
shifting programmers away from a threading model to a task model in order to dis-
entangle resource management (priorities, processor affinities) from the pro-
gramming model (specifying concurrent activities). Other omitted Win32 APIs in-
clude most of the Win32 virtual memory APIs.
Programmers are expected to rely
on the Win32 heap-management APIs rather than attempt to manage memory re-
sources directly.
APIs that were already deprecated in Win32 were also omitted
from the MSDK, as were all ANSI APIs. The MSDK APIs are Unicode only.
The choice of the word
Modern
to describe a product such as Windows is sur-
prising. Perhaps if a new generation Windows is here ten years from now, it will
be referred to as
post-Modern
Windows.
Unlike traditional Win32 processes, the processes running modern applications
have their lifetimes managed by the operating system.
When a user switches away
from an application, the system gives it a couple of seconds to save its state and
then ceases to give it further processor resources until the user switches back to the
application. If the system runs low on resources, the operating system may termi-
nate the application’s processes without the application ever running again. When
the user switches back to the application at some time in the future, it will be re-
started by the operating system.
Applications that need to run tasks in the back-
ground must specifically arrange to do so using a new set of WinRT APIs. Back-
ground activity is carefully managed by the system to improve battery life and pre-
vent interference with the foreground application the user is currently using.
These
changes were made to make Windows function better on mobile devices.
In the Win32 desktop world applications are deployed by running an installer
that is part of the application.
Modern applications have to be installed using Win-
dows’ AppStore program, which will deploy only applications that were uploaded
into the Microsoft on-line store by the developer.
Microsoft is following the same
successful model introduced by Apple and adopted by Android.
Microsoft will not
accept applications into the store unless they pass verification which, among other
checks, ensures that the application is using only APIs available in the MSDK.
When a modern application is running, it always executes in a
sandbox
called
an
AppContainer
.
Sandboxing process execution is a security technique for iso-
lating less trusted code so that it cannot freely tamper with the system or user data.
The Windows AppContainer treats each application as a distinct user, and uses
Windows security facilities to keep the application from accessing arbitrary system
resources. When an application does need access to a system resource, there are
WinRT APIs that communicate to
broker processes
which do have access to more
of the system, such as a user’s files.
As shown in Fig. 11-5, NT subsystems are constructed out of four compo-
nents: a subsystem process, a set of libraries, hooks in
CreateProcess
, and support
in the kernel. A subsystem process is really just a service.
The only special prop-
erty is that it is started by the
smss.exe
(session manager) program—the initial
user-mode program started by NT—in response to a request from
CreateProcess
in Win32 or the corresponding API in a different subsystem.
Although Win32 is
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