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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 204
SEC. 2.6
RESEARCH ON PROCESSES AND THREADS
173
Similarly, much research in the operating systems community these days fo-
cuses on security issues. Numerous incidents have demonstrated that users need
better protection from attackers (and, occasionally, from themselves). One ap-
proach is to track and restrict carefully the information flows in an operating sys-
tem (Giffin et al., 2012).
Scheduling (both uniprocessor and multiprocessor) is still a topic near and dear
to the heart of some researchers. Some topics being researched include energy-ef-
ficient scheduling on mobile devices (Yuan and Nahrstedt, 2006), hyperthread-
ing-aware scheduling (Bulpin and Pratt, 2005), and bias-aware scheduling
(Koufaty, 2010). With increasing computation on underpowered, battery-constrain-
ed smartphones, some researchers propose to migrate the process to a more pow-
erful server in the cloud, as and when useful (Gordon et al., 2012).
However, few
actual system designers are walking around all day wringing their hands for lack of
a decent thread-scheduling algorithm, so it appears that this type of research is
more researcher-push than demand-pull. All in all, processes, threads, and schedul-
ing are not hot topics for research as they once were. The research has moved on to
topics like power management, virtualization, clouds, and security.
2.7 SUMMARY
To hide the effects of interrupts, operating systems provide a conceptual model
consisting of sequential processes running in parallel. Processes can be created and
terminated dynamically.
Each process has its own address space.
For some applications it is useful to have multiple threads of control within a
single process. These threads are scheduled independently and each one has its
own stack, but all the threads in a process share a common address space. Threads
can be implemented in user space or in the kernel.
Processes can communicate with one another using interprocess communica-
tion primitives, for example, semaphores, monitors, or messages. These primitives
are used to ensure that no two processes are ever in their critical regions at the
same time, a situation that leads to chaos.
A process can be running, runnable, or
blocked and can change state when it or another process executes one of the
interprocess communication primitives. Interthread communication is similar.
Interprocess communication primitives can be used to solve such problems as
the producer-consumer, dining philosophers, and reader-writer. Even with these
primitives, care has to be taken to avoid errors and deadlocks.
A great many scheduling algorithms have been studied. Some of these are pri-
marily used for batch systems, such as shortest-job-first scheduling. Others are
common in both batch systems and interactive systems. These algorithms include
round robin, priority scheduling, multilevel queues, guaranteed scheduling, lottery
scheduling, and fair-share scheduling. Some systems make a clean separation be-
tween the scheduling mechanism and the scheduling policy, which allows users to
have control of the scheduling algorithm.
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