essageAdded chapter Writing new policies

git-svn-id: svn://svn.gna.org/svn/sgpemv2/trunk@524 3ecf2c5c-341e-0410-92b4-d18e462d057c
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jinx 2006-03-10 14:46:35 +00:00
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@ -86,7 +86,8 @@ Free Documentation License''.
@unnumbered History
@table @strong
@item 2006, March 10th @r{--- Djina Verbanac}
Added chapter Writing new policies
@item 2006, March 9th @r{--- Djina Verbanac}
Add chapters Overview of SGPEM and Starting with SGPEM.
@item 2006, January 26th @r{--- Matteo Settenvini}
@ -127,8 +128,7 @@ in un Elaboratore Multiprogrammato}'' (in English, ``@emph{Multitasking Computer
Management Simulator}'').
It was initially developed for use inside the ``Operating Systems'' teaching,
part of the Computer Science course of the University of Padova, Italy.
SGPEMv2 is a didactic software, so the main product users are professors and students interested in the simulation of processes.
The aim of SGPEM is to provide an for simulating policies applied to sort processes, and for assigning resources in a multitasking computer. SGPEMv2 is a didactic software, and it can help students to understand better the functionality of Operating Systems.
@c % --------------------------------------------------
@ -362,7 +362,7 @@ install @command{dot}, part of the @emph{Graphviz} package.
@menu
* SGPEM Commands:: Here you find a set of commands available
* SGPEM Commands:: Here you'll find a set of commands available
from the command line
* SGPEM Output:: Interpretation of the output
* Writing new policies:: Steps that must be followed to insert a new policy
@ -380,7 +380,7 @@ install @command{dot}, part of the @emph{Graphviz} package.
@item help @command{<string>}
If <string> is a valid command, it prints the usage instructions for that specific command
@item @command{run}
Advances the simulation by one or more steps, depending on the actual state and on the value sett ed with setmode
Advances the simulation by one or more steps, depending on the actual state and on the value set ed with setmode
@item @command{pause}
It is useful only when the advancement mode is continue. Calling again run will cause the simulation to start from the current simulation step.
@item @command{stop}
@ -414,13 +414,19 @@ If <string> is a valid command, it prints the usage instructions for that specif
@section SGPEM Output
@cindex output
You can seg the textual output of the simulation in your console window or on the GUI window provided with SGPEM v2.
The output of RUN is one or more rows each of which represents the state of the schedulable entities.
It can be RUNNING, READY, BLOCKED, FUTURE or TERMINATED.
The row begins with the number of the instant described by the following lists of states.
The instant 0 represents the INITIAL STATE during which no process is running.
The scheduler activity begins at instant 1. Each schedulable entity is represented by its
name followed by its priority enclosed between round parenthesis.
You can see the textual output of the simulation in your console window or on the GUI window provided with SGPEM v2.
The output of RUN gives you one or more rows, each one representing the state of schedulable entities.
The possible states are: @emph{RUNNING}, @emph{READY}, @emph{BLOCKED}, @emph{FUTURE} or @emph{TERMINATED}.
The row begins with the number of the instant described by the following lists of states:
@itemize
@item instant 0 - represents the INITIAL STATE during which no process is running.
@item instant 1 - the scheduler activity begins.
@end itemize
Each schedulable entity is represented by its name followed by its priority enclosed between round parenthesis.
@c % ------------------------------------------------
@ -428,6 +434,70 @@ name followed by its priority enclosed between round parenthesis.
@section Writing new policies
@cindex policies
All policies are implemented in Python, but don't worry (be happy!). You don't have to be a Python expert to write a new policy.
We'll explain you how to write a new policy on an simple example of FCFS policy. Now let's start, all you have to do is change the few bold-ed lines, of the following example.
@sp 1
@example
01 from Policy import Policy
02 class fcfs(Policy) :
03 def __init__(self):
04 pass;
05 def configure(self):
@strong{06 print 'No options to configure for fcfs'}
07 def is_preemptive(self):
@strong{08 return False}
09 def get_time_slice(self):
@strong{10 return -1}
11 def sort_queue(self, event, queue):
@strong{12 cmpf = lambda a, b: \
a.get_schedulable().get_arrival_time() < \
b.get_schedulable().get_arrival_time()
13 self.sort(queue,cmpf)}
@end example
@sp 2
@itemize
@item body of @code{def configure(self):} line 06 - Configure policy to initial values.
This is called just before a simulation starts, and is responsible to define
the parameters the policy wants to expose to the user. For example, it may make
the return value of is_preemptive configurable, or register an integer value for
a the time slice duration.
@sp 1
@item body of @code{def is_preemptive(self):} line 08 - It says whether the policy wants to be preemptive, other than by normal time slice termination.
The possible return values are:
@enumerate
@item True
If the policy declares it wants the running process to be released if a process at higher priority is put at the beginning of the ready processes queue
@item False
If the policy always waits the end of the time slice (or a process blocking/termination, of course) before selecting a new running process, even if it has greater priority than the current one.
@end enumerate
Please note how the word ``priority'' here has a general meaning: it indicates every process than
can bubble up the sorted ready queue and come before another. So it's up
to Policy.sort_queue() to give it a precise meaning.
@sp1
@item body of @code{def get_time_slice(self):} line 10 - Returns how long is a time-slice for this policy.
A time sliced policy should return a positive integer value, a policy which doesn't use slices should instead
return -1. You're encouraged to use a user-configurable parameter via Policy.configure() if the policy is
time-sliced, to ensure greater flexibility.
@sp 1
@item body of
@code{ def sort_queue(self, event, queue):}
line 12,13 - Sort ready processes queue.
This method is called by the scheduler at each step of the simulation to sort the ready processes queue.
@end itemize
@c % -------------------------------------------------
@c include license text