<s>
Jupiter	B-Language
JVM	I-Language
is	O
an	O
open-source	B-Application
Java	B-Language
virtual	I-Language
machine	I-Language
,	O
which	O
has	O
been	O
developed	O
as	O
a	O
master	O
thesis	O
with	O
modularity	O
and	O
extensibility	O
in	O
mind	O
.	O
</s>
<s>
It	O
uses	O
Boehm	B-Language
garbage	I-Language
collector	I-Language
and	O
GNU	B-Language
Classpath	I-Language
.	O
</s>
<s>
Memory	B-General_Concept
locality	I-General_Concept
-	O
Objects	O
are	O
allocated	O
on	O
the	O
heap	O
with	O
little	O
or	O
no	O
consideration	O
for	O
locality	O
.	O
</s>
<s>
Typically	O
,	O
JVMs	B-Language
employ	O
"	O
stop-the-world	O
"	O
garbage	O
collectors	O
,	O
where	O
program	B-Operating_System
threads	I-Operating_System
are	O
halted	O
during	O
garbage	O
collection	O
.	O
</s>
<s>
Second	O
,	O
using	O
a	O
single	B-Operating_System
thread	I-Operating_System
to	O
collect	O
garbage	O
results	O
in	O
an	O
unacceptably	O
large	O
sequential	O
fraction	O
for	O
any	O
application	O
.	O
</s>
<s>
Memory	B-General_Concept
consistency	I-General_Concept
model	I-General_Concept
-	O
To	O
achieve	O
scaling	O
performance	O
on	O
many	O
processors	O
,	O
it	O
is	O
important	O
to	O
exploit	O
the	O
"	O
relaxed	O
"	O
Java	B-General_Concept
Memory	I-General_Concept
Model	I-General_Concept
.	O
</s>
<s>
Presently	O
no	O
JVM	B-Language
implements	O
the	O
JMM	O
faithfully	O
,	O
and	O
indeed	O
many	O
implement	O
it	O
incorrectly	O
,	O
leading	O
to	O
lack	O
of	O
coherence	O
and	O
loss	O
of	O
optimization	O
opportunities	O
.	O
</s>
<s>
Efficient	O
threads	B-Operating_System
and	O
synchronization	O
-	O
With	O
many	O
processors	O
,	O
it	O
is	O
critical	O
to	O
provide	O
efficient	O
threading	O
support	O
and	O
synchronization	O
mechanisms	O
that	O
scale	O
well	O
.	O
</s>
