Transcript Group 2: Exception Mechanisms

Anirban De
Jeffrey Harry
Yves Lepouchard
Peixin Li
Pinchao Lu
Why we should care about exceptions
Ariane 5 Maiden Flight
 Computer automation is
everywhere:



in your daily life
in critical systems
Exception handling
 Our project deals with:
Java
= THE HOT programming
language

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Java Exception Handling



Exceptions are objects
Multilevel Model
Termination Model
Server
Try {
Workers
Finally
Check
Cleaners }
Catch {
Handlers }
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Receive
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Exception Handling Enhancements
RESCUE-RETRY CONSTRUCT
/* Attempt to transmit a message 100 times and set “tx_successful” */
Public void transmit_message(String message) {
if (tx_failures < 100)
{
attempt_transmission(message);
tx_successful = true;
}
else
tx_successful = false;
/** rescue
{
tx_failures = tx_failures + 1;
retry;
} **/
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Exception Handling Enhancements
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Rescue-Retry added using JJTree and JavaCC
JJTree is a bottom-up Parse Tree Builder
JavaCC uses the output of JJTree to generate the
Lexer/Parser
Generates a top-down, recursive descent parser
Partial EBNF Notation for Rescue-Retry:
void MethodBodyBlock( ) :
{ [ RequireClause( ) ] ( BlockStatement( ) )* [EnsureClause( ) ]
[RescueClause( )] }
void RescueClause( ) :
{ <RESCUE> [ (RescueCatch( ) “;”)+ ] ] <ASSRN_END> }
void RescueCatch( ) :
{ ( "catch" "(" FormalParameter() ")" )? "{" ( BlockStatement() | RetryStatement()
)* “}” }
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Evaluation
Things we sort of already
knew...
Java is slow, more Java is slower.
Given a Java program,
adding more Java is
going to make it larger.
We didn’t know
how much
slower/larger...
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Evaluation
How much slower is Jass?
How much larger?
System 0.33
0.33
User 0.27
4,366
1,081
21.03
1.33
Real
0
22.33
5
10
15
20
25
Execution Time in Seconds
0
1,000
2,000
3,000
4,000
5,000
Buffer w/ Jass
Buffer w/o Jass
Size in Bytes
Buffer class w/ Jass
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Buffer class w/o Jass
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Conclusion
It’s a hog,
it’s slow, it’s
big...
Value inside
(Safe, reusable error-free code.)
BUT...
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Java Exception Handling
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