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