Information Technology Reference
In-Depth Information
Algorithm 2.
isLocalObject(
m
,
O
)
1: Set
staticObject
newObjects
;
2:
for all
stmt ∈ m
do
3:
if
stmt
is a
new
statement
then
4: create a new static object
O
i
;
5:
newObjects
:=
newObjects ∪{O
i
}
;
6:
end if
7:
end for
8:
for all
O
j
∈ newObjects
do
9:
if
O
j
must-alias
O
then
10:
return
true
;
11:
end if
12:
end for
13:
return
false
;
Besides identifying
local objects
, for a configuration, we also need to know
whether it is gotten by statically modeling the multiple consecutive invocations
of the analyzed method in forward or backward analysis. Same as the first op-
timization, we also extend the original configuration tuple to a triple (
Q,b,R
),
where
R
is
true
if the current configuration is indeed gotten by statically mod-
eling the multiple consecutive invocations of the analyzed method.
For a given method
m
, the intra-procedural control-flows cannot lead to the
multiple consecutive invocations of
m
. Hence, the shadows in methods cannot
change the value of
R
. Figure 4 visualizes four types of possible inter-procedural
control-flows (
solid
arrows) of
m
[7]. Solid arrows (1) and (2) are used to model
the transitively recursive method calls to
m
. We cannot determine that a method
call must be transitively recursive at compile-time. Hence, both of the arrows
(3a) and (3b) are used to model the non-recursive method calls within
m
. Addi-
tionally, method
m
can re-executes again after its returning. Arrows (4) is used to
model this case. Obviously, there are only three types of inter-procedural control
flows (
solid
arrows (1), (2) and (4)) in Figure 4, which can lead to the multiple
consecutive invocations of the method
m
. Therefore, in forward analysis, for all
the configurations that reach the entry statements of
m
or the recursive call
sites within
m
along these inter-procedural control flows, we should assign
true
to
R
in these configurations. Based on the same argument, in backward analysis,
the value of
R
in configurations, which reach the exit statements of
m
or the
recursive call sites within
m
along these reverse inter-procedural control flows,
should be assigned
true
. Furthermore, for each initial configuration, the value of
R
is set to
false
in both forward and backward analysis.
Based on Algorithm 2 and the extended configuration, we can filter interferen-
tial configurations as follows: for a given shadow
s
, which is usually a method call
statement, inside a method, if there exists a variable
v
in the variable bindings of
s
pointing to a
local object
, a configuration (
Q,b,R
)in
source
(
s
)or
futures
(
s
)
can be safely eliminated if
R
is
true
. The reason is: even if the shadow
s
and the
configuration have a same static variable binding with respect to the variable
