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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 941
910
CASE STUDY 2: WINDOWS 8
CHAP. 11
resource management is that once a process is in a job, all processes’ threads in
those processes create will also be in the job.
There is no escape.
As suggested by
the name, jobs were designed for situations that are more like batch processing
than ordinary interactive computing.
In Modern Windows, jobs are used to group together the processes that are ex-
ecuting a modern application.
The processes that comprise a running application
need to be identified to the operating system so it can manage the entire application
on behalf of the user.
Figure 11-22 shows the relationship between jobs, processes, threads, and
fibers. Jobs contain processes.
Processes contain threads.
But threads do not con-
tain fibers. The relationship of threads to fibers is normally many-to-many.
job
process
process
thread
thread
thread
thread
thread
fiber
fiber
fiber
fiber
fiber
fiber
fiber
fiber
Figure 11-22.
The relationship between jobs, processes, threads, and fibers.
Jobs and fibers are optional; not all processes are in jobs or contain fibers.
Fibers are created by allocating a stack and a user-mode fiber data structure for
storing registers and data associated with the fiber.
Threads are converted to fibers,
but fibers can also be created independently of threads.
Such a fiber will not run
until a fiber already running on a thread explicitly calls
SwitchToFiber
to run the
fiber.
Threads could attempt to switch to a fiber that is already running, so the pro-
grammer must provide synchronization to prevent this.
The primary advantage of fibers is that the overhead of switching between
fibers is much lower than switching between threads.
A thread switch requires
entering and exiting the kernel. A fiber switch saves and restores a few registers
without changing modes at all.
Although fibers are cooperatively scheduled, if there are multiple threads
scheduling the fibers, a lot of careful synchronization is required to make sure
fibers do not interfere with each other.
To simplify the interaction between threads
and fibers, it is often useful to create only as many threads as there are processors
to run them, and affinitize the threads to each run only on a distinct set of available
processors, or even just one processor.
Each thread can then run a particular subset of the fibers, establishing a one-to-
many relationship between threads and fibers which simplifies synchronization.
Even so there are still many difficulties with fibers. Most of the Win32 libraries
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