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Merge branch 'master' of github.com:jeena/GGS-report

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Jonatan Pålsson 2011-05-12 22:45:58 +02:00
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@ -5190,7 +5190,7 @@ name "sec:Communication-with-the-GDL-VM"
A game launched on the GGS is run within a virtual machine. A game launched on the GGS is run within a virtual machine.
For each programming language supported, there is a virtual machine which For each programming language supported, there is a virtual machine which
interprets the game. interprets the game.
Furthermore an interface for communication between the GGS, the game and Furthermore an interface for communication among the GGS, the game and
the players playing the game is present. the players playing the game is present.
\end_layout \end_layout
@ -5218,7 +5218,7 @@ localStorage
. .
The game state is safely stored in a database and retrieved for manipulation The game state is safely stored in a database and retrieved for manipulation
by a call for the world object. by a call for the world object.
Interaction with the players is done by using the Interaction with the players are done by using the
\emph on \emph on
\begin_inset ERT \begin_inset ERT
@ -5315,7 +5315,7 @@ reference "alg:exposing-erlang"
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
In JavaScript is is common to use a top level object, called a global object, In JavaScript it is common to use a top level object, called a global object,
to establish a global scope. to establish a global scope.
This allows the declaration of global variables and functions. This allows the declaration of global variables and functions.
To gain access to the global object in the GGS, the To gain access to the global object in the GGS, the
@ -5390,7 +5390,7 @@ localStorage
\noun default \noun default
objects are dummy objects, which provide no functionality, these two objects objects are dummy objects, which provide no functionality, these two objects
are simply placed in the GDL for the purpose clearing up the code. are simply placed in the GDL for the purpose clearing up the code.
In order to perform an action using the GGS and To perform an action using the GGS and
\noun on \noun on
localStorage localStorage
\noun default \noun default
@ -5840,7 +5840,7 @@ Techniques for ensuring reliability
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
One of the main goals of the project is to achieve high reliability. One main goal of the project is to achieve high reliability.
The term 'reliable system' is defined by the IEEE as The term 'reliable system' is defined by the IEEE as
\end_layout \end_layout
@ -6048,7 +6048,7 @@ key "Savor:1997:HSA:851010.856089"
There are several approaches to supervisor design in general (when not just There are several approaches to supervisor design in general (when not just
considering how they work in Erlang). considering how they work in Erlang).
One common approach is to have the supervisor look in to the state of the One common approach is to have the supervisor look in to the state of the
process(es) it supervises, and let the supervisor make decisions based process(es) it supervises, and let the supervisor makes decisions based
on this state. on this state.
The supervisor has a specification of how the process it supervises should The supervisor has a specification of how the process it supervises should
function, this is how it makes decisions. function, this is how it makes decisions.
@ -6060,18 +6060,17 @@ In Erlang, there is a simple version of supervisors.
No state of the processes being supervised is inspected. No state of the processes being supervised is inspected.
There is, however a specification of how the supervised processes should There is, however a specification of how the supervised processes should
behave, but on a higher level. behave, but on a higher level.
The specification describes things such as how many times in a given time The specification describes things such as how many times in a given interval a child process may crash, which processes need restarting when
interval a child process may crash, which processes need restarting when
crashes occur, etc. crashes occur, etc.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
When the linking of processes in order to monitor exit behavior is coupled When the linking of processes to monitor exit behavior is coupled with the
with the transparent distribution of Erlang, a very powerful supervision transparent distribution of Erlang, a very powerful supervision system
system is created. is created.
For instance, we can restart a failing process on a different, new node, For instance, it is possible to restart a failing process on a different,
with minimal impact on the system as a whole. new node, with minimal impact on the system as a whole.
\end_layout \end_layout
@ -6114,28 +6113,28 @@ reference "fig:The-supervisor-structure"
subsystem. subsystem.
Since these two systems perform very different tasks they have been separated. Since these two systems perform very different tasks they have been separated.
Each subsystem has one worker process, the coordinator or the dispatcher. Each subsystem has one worker process, the coordinator or the dispatcher.
The worker process keeps a state which should not be lost upon a crash. The worker process keeps a state which should not be lost on a crash.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
A choice has been made to let faulty processes crash very easily when they A choice has been made to let faulty processes crash very easily when they
receive bad data, or something unexpected happens. receive bad data, or something unexpected happens.
The alternative to crashing would have been to try and fix this faulty The alternative to crashing would have been to try to fix this faulty
data, or to foresee the unexpected events. data, or to foresee the unexpected events.
This was not chosen since it is so simple to monitor and restart processes, This was not chosen since it is so simple to monitor and restart processes,
and so difficult to try and mend broken states. and so difficult to try to mend broken states.
This approach is something widely deployed in the Erlang world, and developers This approach is something widely deployed in the Erlang world, and developers
are often encouraged to “Let it crash”. are often encouraged to “Let it crash”.
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
To prevent any data loss, the good state of the worker processes is stored To prevent any data loss, the good state of the worker processes are stored
in their respective backup processes. in their respective backup processes.
When a worker process (re)starts, the backup process is queried for any When a worker process (re)starts, the backup process is queried for any
previous state, if there is any, that state is loaded in to the worker previous state, if there is any, that state is loaded in to the worker
and it proceeds where it left off. and it proceeds where it left off.
If on the other hand no state is available, a special message is delivered If on the other hand no state is available, a special message is delivered
instead, making the worker create a new state, this is what happens when instead, making the worker creates a new state, this is what happens when
the workers are first created. the workers are first created.
\end_layout \end_layout