Page 35 - DCAP103_Principle of operating system

Principles of Operating Systems

Notes end
remove(resource, available);
end

procedure release(resource: R);
var process: P;
region v do
begin enter(resource, available);

if not empty(requests) then
begin remove(process, requests);
cause(grant[process]);
end

end
Algorithm 3: Scheduling of heavily used resources

If the scheduling rule is completely unknown to the programmer as before, additional variables
are required to ensure that resources granted to waiting processes remain available to them until
they reenter their critical regions.
Algorithm 3 is a simple example of completely controlled resource allocation. A number
of processes share a pool of equivalent resources. Processes and resources are identified by
indices of type P and R respectively. When resources are available, a process can acquire one
immediately; otherwise, it must enter a request in a data structure of type set of P and wait
until a resource is granted to it. It is assumed that the program controls the entry and removal
of set elements completely.

Conclusion
The essential properties of these concepts are:
1. A distinction between disjoint and interacting processes;

2. An association of shared data with operations defined on them;
3. Mutual exclusion of these operations in time;

4. Synchronizing primitives which permit partial or complete control of process
scheduling.

1.7.5.5 Multiprocessing
Multiprocessing is the use of two or more central processing units (CPUs) within a single
computer system. The term also refers to the ability of a system to support more than one
processor and/or the ability to allocate tasks between them. There are many variations on this
basic theme, and the definition of multiprocessing can vary with context, mostly as a function
of how CPUs are defined.
Multiprocessing sometimes refers to the execution of multiple concurrent software processes
in a system as opposed to a single process at any one instant. However, the terms multitasking
or multiprogramming are more appropriate to describe this concept, which is implemented

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