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Jeena Paradies 2011-05-12 18:14:20 +02:00
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@ -2858,14 +2858,14 @@ textbf{UUID}}{Universally Unique Identifier}
\end_layout \end_layout
\begin_layout Standard \begin_layout Standard
Inside the GGS everything has a unique identifier. Inside the GGS everything needs a unique identifier.
There are identifiers for players, tables and other resources. There are identifiers for players, tables and other resources.
When players communicate amongst each other or communicate with tables, When players communicate amongst each other or with tables, they need to
they need to be able to uniquely identify all of these resources. be able to uniquely identify all of these resources.
Within one machine, this is mostly not a problem. Within one machine, this is mostly not a problem.
A simple system with a counter can be imagined, where each request for A simple system with a counter can be imagined, where each request for
a new ID increments the previous identifier and returns the new identifier a new ID increments the previous identifier and returns the new identifier
based off the old one, see algorithm based on the old one; see algorithm
\begin_inset CommandInset ref \begin_inset CommandInset ref
LatexCommand ref LatexCommand ref
reference "alg:A-simple-generator" reference "alg:A-simple-generator"
@ -2887,14 +2887,25 @@ reference "alg:A-simple-generator"
\begin_layout Standard \begin_layout Standard
The obvious solution to this problem is to ensure mutual exclusion by using The obvious solution to this problem is to ensure mutual exclusion by using
some sort of lock, which may work well in many concurrent systems. some sort of a lock, which may work well in many concurrent systems.
In a distributed system, this lock, along with the state, would have to In a distributed system, like the GGS, this lock, along with the state,
be distributed. would have to be distributed.
If the lock is not distributed, no guarantee can be made that two nodes If the lock is not distributed, no guaranties can be made that two nodes
in the distributed system do not generate the same number. in the distributed system do not generate the same identifier.
\end_layout
\begin_layout Standard
A different approach is to give each node the ability to generate Universally A different approach is to give each node the ability to generate Universally
Unique Identifiers (UUID), where the state of one machine does not interfere Unique Identifiers (UUID), where the state of one machine does not interfere
with the state of another. with the state of another.
According to
\begin_inset CommandInset citation
LatexCommand citet
key "Leach98uuidsand"
\end_inset
:
\begin_inset ERT \begin_inset ERT
status open status open
@ -2923,26 +2934,14 @@ textbf{SHA-1}}{Cryptigraphic hash function, designed by the National Security
\end_layout \end_layout
\begin_layout Standard \begin_layout Quote
According to
\begin_inset CommandInset citation
LatexCommand citet
key "Leach98uuidsand"
\end_inset
,
\begin_inset Quotes eld
\end_inset
A UUID is 128 bits long, and if generated according to the one of the mechanisms A UUID is 128 bits long, and if generated according to the one of the mechanisms
in this document, is either guaranteed to be different from all other UUIDs/GUI in this document, is either guaranteed to be different from all other UUIDs/GUI
Ds generated until 3400 A.D. Ds generated until 3400 A.D.
or extremely likely to be different or extremely likely to be different.
\begin_inset Quotes erd \end_layout
\end_inset
. \begin_layout Standard
The generation of a UUID is accomplished by gathering several different The generation of a UUID is accomplished by gathering several different
sources of information, such as: time, MAC addresses of network cards, sources of information, such as: time, MAC addresses of network cards,
and operating system data, such as percentage of memory in use, mouse cursor and operating system data, such as percentage of memory in use, mouse cursor
@ -2967,7 +2966,7 @@ reference "alg:A-simple-generator"
\end_inset \end_inset
with mutual exclusion, it is not possible to have identifier collisions with mutual exclusion, it is extremly unlikely to have identifier collisions
when recovering from network splits between the GGS clusters. when recovering from network splits between the GGS clusters.
Consider figure Consider figure
\begin_inset CommandInset ref \begin_inset CommandInset ref