documentation/minutes/minutes-20001113b.txt

Minutes of Meeting, 13/11/2000 @ 14:00
Location: Eliot College, E3E room 8

Present: ajm4, tdb1
Absent: none

[tdb1: Documented by ajm4, comments added by tdb1.]

This meeting was between ajm4 and tdb1 to discuss and
possibly implement parts of the CORE and FilterManager
elements of the system.


Initial discussion was on the configuration system of the
CORE which has been partially completed to date.  A key
decision that was made was that it will NOT be possible
for the elements of the system to update their own
configuration, as this will cause difficulties if the user
wants to use the file themseleves (ie, add comments).  This
isn't seen to be a real problem though, as it was only going
to be a "funky" extra ;-)

[tdb1: this will also solve security issues with 
       unauthorised third parties changing settings.]


Next point was whether or not we would support elements
being able to be updated without restarting them, ie. a host
would be able to detect its configuration has changed and 
adjust accordingly.  The method chosen was to use the last
modified date stamp of the configuration file as an
indicator.  When a Configuration object is passed to an
element of the system it can determine when the loaded
configuration was last edited.  The element of the system
can then periodically (the period can be set in the
configuration ;-) ) ask the Configurator if its
configuration has been updated, and act accordingly.  The
methods: 

     long Configuration.getLastModifed() and
  boolean Configurator.isModified(String conf, long curTime)

where thus implemented and the configurator test class
modified to include a test of this system.

It should also be noted at this stage that a java 'long' is 
defined as a 'long long' in the IDL->Java mapping.


The next item discussed was the CORBA IDL and general system
package structure.  It was decided to use the ukc domain as
the root identifier for the project.  Packages therefore
follow the naming:

    uk.ac.ukc.iscream.<package>.<class>|<sub-package>
    
The IDL and currently implemented classes were updated to 
refelect this change.


The next item to be discussed was the initial thinking and
possible implementation of the FilterManager.  An initial
FilterManager class was fleshed out with hooks to the logger
and the configurator, it then creates a FilterListener class
which will listen for new Hosts trying to connect to the
system.  It was NOT decided how Hosts should find the system
however a method similar to the WPAD system used to locate
web caches was suggested by tdb1.

A Host contacts the FilterManager to initialise itself and
obtain a host and port number of a Filter that it will talk
to. When the FilterListener is contacted by a host it spawns
a HostInit object to handle this intialisation.  The first
thing a Host does is obtain its configuration, this is done
by the HostInit object obtaining the configuration of the
host on its behalf.  An initial protocol of how this system
works is as follows (of course this is subject to later
alteration, but seemed like a "good idea at the time"):

Host                    FilterManager.HostInit
    STARTCONFIG ->
                        <- OK | ERROR
    LASTMODIFIED ->
                        <- LASTMODIFIED
    DO {
        PROPERTY ->
                        <- VALUE | ERROR
    } UNTIL GOT CONFIG
    
    ENDCONFIG ->
                        <- OK

If there is an ERROR returned after STARTCONFIG, this
indicates to the Host that there is no configuration 
available for it at this time.  It may be possible to
continue using default values, but this is up to the host
configuration.  Again, this is not a certain feature and
should be discussed with other members of the group.

If the property section returns an ERROR then this indicates
to the host that that property requested doesn't exist, the
Host will then deal with this either by ending with an error
on the local system or by ignoring it if it can.

The above features were implemented.


The next item needed to be developed is an architecture for
FilterParent's and FilterChild's, as the next stage of Host 
initialisation is to be passed a 'reference' to a
FilterChild.  This 'reference' will be a server and a port
and not a reference in the CORBA or Java way of thinking.

It was noted that on a "heart beat" with the system, a Host
should check to see if its configuration has changed.  If it
has it should then re-initialise itself.  This will allow 
configuration changes to be made to any part of the system
knowing that on the next "heart beat" the configuration will
take effect.  A point to note about this is that if there is
an error in the configuration the Host will simply error and
die.  What we may want (but still undecided) is a constant
retry until the config is ok.  So the system administrator 
will see in the logger destination that there has been an
error in this new configuration and can make changes to 
rectify the problem, without having to interact with the 
Host program itself.


All code generated was placed in the "experimental" tree of
CVS, awaiting approval from other group members.  It should
also be noted that although CVS records tdb1 as the 
'checker inner', it was infact ajm4...as he was the king of
code during this meeting ;-p

Many small bug fixes were made to the existing code.

It was also noted that there is a need for coding standards.

As we had reached an appropriate stage to end, and given the
late hour, it was decided to conclude the meeting.  It was,
after all, nearly 7 hours of coding ;-)

Since this meeting took place tdb1 has produced Makefiles
to allow easy compiling and configuration of the code.


Meeting was concluded @ 20:45. Next meeting booked for 11:00 
on Wednesday, until 12:30. Meeting with iau @ 13:30 on that 
day.
Revision:	1.3
Committed:	Wed Nov 15 00:33:45 2000 UTC (23 years, 5 months ago) by ajm
Content type:	text/plain
Branch:	MAIN
Changes since 1.2:	+24 -18 lines
Log Message:	added tdb1's updates and other extras
#	Content
1	Minutes of Meeting, 13/11/2000 @ 14:00
2	Location: Eliot College, E3E room 8
3
4	Present: ajm4, tdb1
5	Absent: none
6
7	[tdb1: Documented by ajm4, comments added by tdb1.]
8
9	This meeting was between ajm4 and tdb1 to discuss and
10	possibly implement parts of the CORE and FilterManager
11	elements of the system.
12
13
14
15	Initial discussion was on the configuration system of the
16	CORE which has been partially completed to date. A key
17	decision that was made was that it will NOT be possible
18	for the elements of the system to update their own
19	configuration, as this will cause difficulties if the user
20	wants to use the file themseleves (ie, add comments). This
21	isn't seen to be a real problem though, as it was only going
22	to be a "funky" extra ;-)
23
24	[tdb1: this will also solve security issues with
25	unauthorised third parties changing settings.]
26
27
28	Next point was whether or not we would support elements
29	being able to be updated without restarting them, ie. a host
30	would be able to detect its configuration has changed and
31	adjust accordingly. The method chosen was to use the last
32	modified date stamp of the configuration file as an
33	indicator. When a Configuration object is passed to an
34	element of the system it can determine when the loaded
35	configuration was last edited. The element of the system
36	can then periodically (the period can be set in the
37	configuration ;-) ) ask the Configurator if its
38	configuration has been updated, and act accordingly. The
39	methods:
40
41	long Configuration.getLastModifed() and
42	boolean Configurator.isModified(String conf, long curTime)
43
44	where thus implemented and the configurator test class
45	modified to include a test of this system.
46
47	It should also be noted at this stage that a java 'long' is
48	defined as a 'long long' in the IDL->Java mapping.
49
50
51	The next item discussed was the CORBA IDL and general system
52	package structure. It was decided to use the ukc domain as
53	the root identifier for the project. Packages therefore
54	follow the naming:
55
56	uk.ac.ukc.iscream.<package>.<class>\|<sub-package>
57
58	The IDL and currently implemented classes were updated to
59	refelect this change.
60
61
62
63	The next item to be discussed was the initial thinking and
64	possible implementation of the FilterManager. An initial
65	FilterManager class was fleshed out with hooks to the logger
66	and the configurator, it then creates a FilterListener class
67	which will listen for new Hosts trying to connect to the
68	system. It was NOT decided how Hosts should find the system
69	however a method similar to the WPAD system used to locate
70	web caches was suggested by tdb1.
71
72	A Host contacts the FilterManager to initialise itself and
73	obtain a host and port number of a Filter that it will talk
74	to. When the FilterListener is contacted by a host it spawns
75	a HostInit object to handle this intialisation. The first
76	thing a Host does is obtain its configuration, this is done
77	by the HostInit object obtaining the configuration of the
78	host on its behalf. An initial protocol of how this system
79	works is as follows (of course this is subject to later
80	alteration, but seemed like a "good idea at the time"):
81
82	Host FilterManager.HostInit
83	STARTCONFIG ->
84	<- OK \| ERROR
85	LASTMODIFIED ->
86	<- LASTMODIFIED
87	DO {
88	PROPERTY ->
89	<- VALUE \| ERROR
90	} UNTIL GOT CONFIG
91
92	ENDCONFIG ->
93	<- OK
94
95	If there is an ERROR returned after STARTCONFIG, this
96	indicates to the Host that there is no configuration
97	available for it at this time. It may be possible to
98	continue using default values, but this is up to the host
99	configuration. Again, this is not a certain feature and
100	should be discussed with other members of the group.
101
102	If the property section returns an ERROR then this indicates
103	to the host that that property requested doesn't exist, the
104	Host will then deal with this either by ending with an error
105	on the local system or by ignoring it if it can.
106
107	The above features were implemented.
108
109
110
111	The next item needed to be developed is an architecture for
112	FilterParent's and FilterChild's, as the next stage of Host
113	initialisation is to be passed a 'reference' to a
114	FilterChild. This 'reference' will be a server and a port
115	and not a reference in the CORBA or Java way of thinking.
116
117	It was noted that on a "heart beat" with the system, a Host
118	should check to see if its configuration has changed. If it
119	has it should then re-initialise itself. This will allow
120	configuration changes to be made to any part of the system
121	knowing that on the next "heart beat" the configuration will
122	take effect. A point to note about this is that if there is
123	an error in the configuration the Host will simply error and
124	die. What we may want (but still undecided) is a constant
125	retry until the config is ok. So the system administrator
126	will see in the logger destination that there has been an
127	error in this new configuration and can make changes to
128	rectify the problem, without having to interact with the
129	Host program itself.
130
131
132
133	All code generated was placed in the "experimental" tree of
134	CVS, awaiting approval from other group members. It should
135	also be noted that although CVS records tdb1 as the
136	'checker inner', it was infact ajm4...as he was the king of
137	code during this meeting ;-p
138
139	Many small bug fixes were made to the existing code.
140
141	It was also noted that there is a need for coding standards.
142
143	As we had reached an appropriate stage to end, and given the
144	late hour, it was decided to conclude the meeting. It was,
145	after all, nearly 7 hours of coding ;-)
146
147	Since this meeting took place tdb1 has produced Makefiles
148	to allow easy compiling and configuration of the code.
149
150
151	Meeting was concluded @ 20:45. Next meeting booked for 11:00
152	on Wednesday, until 12:30. Meeting with iau @ 13:30 on that
153	day.