Transcript No Slide Title

CIS 644 Thus. Oct. 28, 1999
… misc. questions
… thread, Runable
… communication patterns
W10B
Exam1 …
covers: class & scenario models
open book … < 1.5 hours
Tues Nov 2.
on campus … in class
off campus … sent email 4:30pm C.T.
email or fax it back
administrative:
> corrections to GRADES file are being
made … will be reposted later.
> CIS web server was “killed” this week …
temporarily moved …
… some scripts may not work
CIS644 local pages should be OK now.
> I keep up with “urgent” email …
rest may wait for a while
(will post patterns lists later)
?? are GRADES 4 digits SSN number?
... they are KSU student ID number.
?? send back off-campus homework
… no … just class discussion
?? post “my answer”
… no … posted TA’s answer
?? “1.5” hours for exam
… on-campus ... up to 90 minutes
… off-campus … honor system
will draw some diagrams …
FAX is OK … “asap”
if you want to use Rose or other tool,
great … don’t count that as part of
exam time.
review questions:
"class variables" ,
"class markers" (page 21)
c getList( ; list)
… there are times with class methods
are required
Coad’s use of class methods for
collections is optional …
not my preference
my preference:
theAirports
LOOP
|
getAirport( ; anAirport) -->|
|
anAirport
|
|
getInfo( ) ----------------------->|
ENDLOOP
translates:
loop {
anAirport = theAirports.getAirport( i );
}
??is this related to
aggregation vs composition ??
… no … I see A vs C as
who owns the items
who is responsible for keeping refs
UML … what are the items "part of"
??
c new(passenger; aReservation)
… converts to Java as:
aReservation =
new Reservation(passenger)
??
Airports
|
c remove( anAirport) -->|
could translate as:
class Airports {
Airport[ ] items;
…
void remove( integer i)
{ items[ i ] = null ; }
}
??
* getValues( ; values)
… * indicates a loop …
calls to multiple objects from
the collection
threads use comments:
threads are used in:
CIS625 distributed Processing
CIS725 Computer Networks
I use Solaris threads & Posix threads.
I use the ACE framework
(thread details are hidden within)
… at Motorola
at Sprint:
...Every application … is multi-threaded
... created our own thread classes in C++
( inconsistencies with the standard class)
e.g.
* credit card validation (C++) …
allows concurrent requests
* vendor communication (C++) …
allows concurrent requests
* orders system (Java) ..
Enterprise Java Beans framework
(hidden multi-threads )
.. some Java threads.
.. more with multi-tasking in real-time OS
(OS-9, iRMX, Unison, VersaDos) using C
…these OS's have features such as:
mailboxes, signals, shared memory
for intertask communication
semaphores to control access
we use concurrency
...in modeling aircraft systems
for real-time simulation
-----------------------------------------------------
threads (multiple processes)
are becoming more common
in systems we are developing
?? was there only one thread
in the Video Store??
… Chap 1 … yes
… real… no…
need to define the "system" arch.
assume: one processor, many agents
in PD … should be multiple Agent tasks,
each with own UI
continuing into Chaps 4 & 5:
Coad: "this is easy"
UML:
:-(
objects: passive vs active
active: process vs thread
ADA: object vs task
Java:
Runable interface
defines run()
but is not per se active object
Thread implements Runable
and is active object
Runable object can be executed "in"
(with ??) its own thread.
… pass object to Thread(Obj) .
or, Runable object can make its own
thread, as Sensor version p. 194
or ..
Thread can execute several different
runable objects (…invoke their run() )
… in sequence , of course.
threads can have priorities …
but current JVMs do not guarentee
exact mapping of priorities !!
Lea recommends:
HI … for system critical threads
LO … for background threads
Coad mapping … p. 192 :-(
visual representation of active objects:
… at Java level,
only Thread is really active,
… at design (abstract) level,
Runable objects can be "active"
:-( Coad does not show bold boxes
__
__
Ada: /__ / for Task vs [__] for obj.
skim Chap 4, 5 for overview:
several different forms for communication
passive (polling)
timer
active (source notifies its listeners)
message vs notification:
of course, at Java level,
notification implemented as message
End