<s>
ProbeVue	B-Operating_System
is	O
IBM	O
's	O
implementation	O
of	O
a	O
lightweight	O
dynamic	O
tracing	O
environment	O
introduced	O
in	O
AIX	B-Application
version	O
6.1	O
.	O
</s>
<s>
ProbeVue	B-Operating_System
provides	O
the	O
ability	O
to	O
probe	O
running	O
processes	O
in	O
order	O
to	O
provide	O
statistical	O
analysis	O
as	O
well	O
as	O
retrieve	O
data	O
from	O
the	O
probed	O
process	O
.	O
</s>
<s>
The	O
dynamic	O
nature	O
of	O
ProbeVue	B-Operating_System
allows	O
it	O
to	O
be	O
used	O
as	O
a	O
global	O
system	O
performance	O
tool	O
while	O
retaining	O
the	O
ability	O
to	O
drill	O
into	O
very	O
specific	O
events	O
on	O
a	O
single	O
process	O
or	O
thread	O
.	O
</s>
<s>
Because	O
modifications	O
are	O
not	O
required	O
of	O
a	O
probed	O
process	O
or	O
system	O
and	O
the	O
lightweight	O
design	O
of	O
ProbeVue	B-Operating_System
as	O
a	O
tracing	O
tool	O
,	O
it	O
is	O
suitable	O
for	O
use	O
in	O
a	O
production	O
environment	O
where	O
previous	O
tracing	O
tools	O
would	O
have	O
been	O
performance	O
prohibitive	O
.	O
</s>
<s>
ProbeVue	B-Operating_System
provides	O
a	O
series	O
of	O
probe	O
point	O
specifications	O
that	O
are	O
potential	O
events	O
that	O
can	O
be	O
probed	O
.	O
</s>
<s>
A	O
script	O
written	O
in	O
the	O
Vue	B-Operating_System
language	O
allows	O
the	O
user	O
to	O
define	O
a	O
probe	O
that	O
is	O
a	O
block	O
of	O
code	O
called	O
an	O
action	O
block	O
that	O
will	O
run	O
when	O
those	O
events	O
occur	O
on	O
the	O
system	O
.	O
</s>
<s>
The	O
code	O
in	O
the	O
action	O
block	O
follows	O
a	O
C-like	O
syntax	O
with	O
a	O
limited	O
set	O
of	O
built	O
in	O
functions	O
.	O
</s>
<s>
The	O
first	O
line	O
in	O
the	O
action	O
block	O
is	O
a	O
C-style	O
comment	O
and	O
therefore	O
will	O
not	O
execute	O
in	O
the	O
ProbeVue	B-Operating_System
environment	O
.	O
</s>
<s>
The	O
ProbeVue	B-Operating_System
environment	O
protects	O
the	O
user	O
from	O
errant	O
code	O
or	O
resource	O
hungry	O
tracing	O
frequently	O
seen	O
with	O
previous	O
IBM	O
tracing	O
tools	O
.	O
</s>
<s>
The	O
runtime	O
compile	O
feature	O
of	O
ProbeVue	B-Operating_System
provides	O
a	O
powerful	O
ad	O
hoc	O
environment	O
for	O
data	O
gathering	O
.	O
</s>
<s>
Currently	O
IBM	O
provides	O
the	O
following	O
probe	O
providers	O
on	O
AIX	B-Application
6.1	O
:	O
syscall	O
,	O
uft	O
,	O
interval	O
,	O
trace	O
,	O
and	O
the	O
probevue	B-Operating_System
probes	O
(	O
BEGIN	O
and	O
END	O
)	O
.	O
</s>
<s>
User	O
Function	O
Tracing	O
(	O
uft	O
)	O
probes	O
can	O
be	O
defined	O
for	O
entry	O
points	O
of	O
functions	O
defined	O
in	O
a	O
C	B-Language
or	O
C++	B-Language
program	I-Language
.	O
</s>
<s>
Both	O
syscall	O
and	O
uft	O
probes	O
must	O
include	O
a	O
valid	O
function	O
prototype	O
in	O
the	O
Vue	B-Operating_System
script	O
before	O
function	O
parameters	O
(	O
for	O
the	O
entry	O
probes	O
)	O
or	O
return	O
values	O
(	O
for	O
syscall	O
exit	O
probes	O
only	O
)	O
can	O
be	O
accessed	O
.	O
</s>
<s>
The	O
trace	O
provider	O
allows	O
ProbeVue	B-Operating_System
to	O
access	O
traditional	O
trace	O
hooks	O
.	O
</s>
<s>
Finally	O
the	O
probevue	B-Operating_System
probes	O
called	O
BEGIN	O
and	O
END	O
will	O
fire	O
as	O
the	O
probevue	B-Operating_System
environment	O
itself	O
starts	O
and	O
exits	O
.	O
</s>
<s>
Because	O
ProbeVue	B-Operating_System
is	O
designed	O
as	O
a	O
tool	O
to	O
monitor	O
operating	O
system	O
events	O
,	O
the	O
Vue	B-Operating_System
language	O
uses	O
an	O
event	B-Application
driven	I-Application
style	O
that	O
is	O
used	O
to	O
describe	O
how	O
to	O
process	O
data	O
derived	O
from	O
these	O
events	O
.	O
</s>
<s>
Like	O
most	O
dynamic	O
tracing	O
languages	O
found	O
on	O
other	O
Unices	O
,	O
the	O
Vue	B-Operating_System
language	O
has	O
a	O
C-like	O
syntax	O
and	O
is	O
frequently	O
presented	O
in	O
this	O
context	O
.	O
</s>
<s>
Vue	B-Operating_System
's	O
relationship	O
to	O
C	B-Language
has	O
many	O
parallels	O
but	O
deviates	O
most	O
significantly	O
from	O
the	O
imperative	B-Application
nature	O
of	O
C	B-Language
.	O
Some	O
of	O
the	O
contrasts	O
and	O
similarities	O
are	O
shown	O
here	O
.	O
</s>
<s>
Because	O
ProbeVue	B-Operating_System
is	O
used	O
to	O
monitor	O
applications	O
written	O
primarily	O
in	O
C	B-Language
,	O
it	O
supports	O
all	O
C	B-Language
data	O
types	O
as	O
well	O
as	O
C	B-Language
data	O
structures	O
.	O
</s>
<s>
Vue	B-Operating_System
also	O
supports	O
a	O
String	O
,	O
list	O
,	O
and	O
time	O
stamp	O
data	O
types	O
.	O
</s>
<s>
The	O
String	O
and	O
list	O
types	O
are	O
both	O
actually	O
arrays	B-Data_Structure
,	O
while	O
the	O
time	O
stamp	O
is	O
a	O
high	O
resolution	O
representation	O
of	O
a	O
point	O
in	O
time	O
.	O
</s>
<s>
Type	O
casting	O
and	O
automatic	O
type	O
promotion	O
during	O
operations	O
with	O
mixed	O
types	O
is	O
similar	O
to	O
C	B-Language
behavior	O
as	O
well	O
.	O
</s>
<s>
Pointers	O
to	O
arrays	B-Data_Structure
and	O
data	O
structures	O
behave	O
in	O
ProbeVue	B-Operating_System
the	O
same	O
as	O
they	O
would	O
in	O
a	O
C	B-Language
program	I-Language
,	O
with	O
the	O
key	O
difference	O
from	O
C	B-Language
is	O
that	O
when	O
pointers	O
refer	O
to	O
a	O
location	O
in	O
memory	O
they	O
are	O
referencing	O
a	O
location	O
in	O
another	O
process	O
space	O
.	O
</s>
<s>
To	O
access	O
that	O
memory	O
it	O
is	O
necessary	O
to	O
first	O
copy	O
the	O
memory	O
location	O
into	O
the	O
local	O
ProbeVue	B-Operating_System
environment	O
.	O
</s>
<s>
If	O
the	O
memory	O
has	O
been	O
paged	O
out	O
,	O
ProbeVue	B-Operating_System
cannot	O
force	O
a	O
page	B-General_Concept
fault	I-General_Concept
to	O
access	O
it	O
.	O
</s>
<s>
Another	O
difference	O
is	O
that	O
the	O
size	O
of	O
pointers	O
in	O
C	B-Language
are	O
determined	O
at	O
compile	O
time	O
,	O
while	O
in	O
ProbeVue	B-Operating_System
they	O
are	O
determined	O
by	O
the	O
32	O
or	O
64	B-Device
bitness	O
of	O
the	O
application	O
that	O
is	O
probed	O
.	O
</s>
<s>
Vue	B-Operating_System
uses	O
scoping	B-Language
rules	I-Language
similar	O
to	O
C	B-Language
,	O
but	O
must	O
also	O
account	O
for	O
the	O
externally	O
derived	O
nature	O
of	O
much	O
of	O
the	O
data	O
in	O
probes	O
.	O
</s>
<s>
Vue	B-Operating_System
operators	O
follow	O
C	B-Language
conventions	O
closely	O
with	O
the	O
exception	O
of	O
when	O
used	O
with	O
strings	O
.	O
</s>
<s>
Vue	B-Operating_System
does	O
not	O
allow	O
the	O
definition	O
of	O
user	O
functions	O
,	O
recursion	O
,	O
or	O
looping	O
constructs	O
but	O
does	O
offer	O
conditional	O
if-then	O
expressions	O
within	O
a	O
probe	O
action	O
block	O
.	O
</s>
<s>
The	O
lightweight	O
nature	O
of	O
ProbeVue	B-Operating_System
prohibits	O
a	O
Vue	B-Operating_System
script	O
from	O
defining	O
expensive	O
looping	O
or	O
extensive	O
branching	O
operations	O
that	O
could	O
degrade	O
performance	O
.	O
</s>
<s>
This	O
works	O
conceptually	O
much	O
like	O
transaction	O
controls	O
in	O
SQL	B-Language
.	O
</s>
<s>
A	O
Vue	B-Operating_System
script	O
can	O
be	O
invoked	O
with	O
interpreter	O
magic	B-Operating_System
and	O
set	O
executable	O
like	O
a	O
shell	O
script	O
or	O
can	O
be	O
run	O
as	O
input	O
to	O
the	O
probevue	B-Operating_System
command	O
in	O
the	O
form	O
of	O
a	O
command	O
line	O
parameter	O
or	O
stdin	O
input	O
.	O
</s>
<s>
By	O
convention	O
,	O
Vue	B-Operating_System
scripts	O
have	O
a	O
.e	O
filename	O
extension	O
.	O
</s>
<s>
The	O
Vue	B-Operating_System
language	O
lacks	O
aggregations	O
and	O
instead	O
uses	O
a	O
list	O
data	O
type	O
that	O
offers	O
similar	O
yet	O
limited	O
functionality	O
.	O
</s>
<s>
The	O
equivalent	O
product	O
from	O
Solaris	B-Application
called	O
DTrace	B-Application
offers	O
an	O
aggregation	O
data	O
type	O
and	O
a	O
powerful	O
set	O
of	O
aggregating	O
functions	O
to	O
represent	O
statistical	O
data	O
.	O
</s>
<s>
The	O
list	O
data	O
type	O
offers	O
only	O
basic	O
aggregating	O
functions	O
on	O
a	O
single	O
item	O
(	O
as	O
opposed	O
to	O
an	O
associative	B-Application
arrays	I-Application
of	O
aggregations	O
that	O
DTrace	B-Application
offers	O
)	O
.	O
</s>
<s>
IBM	O
has	O
committed	O
to	O
associative	B-Application
arrays	I-Application
on	O
future	O
versions	O
of	O
the	O
Vue	B-Operating_System
language	O
.	O
</s>
<s>
Because	O
of	O
the	O
long	O
development	O
lead	O
time	O
DTrace	B-Application
has	O
over	O
ProbeVue	B-Operating_System
,	O
DTrace	B-Application
has	O
considerably	O
more	O
probe	O
point	O
specifications	O
.	O
</s>
<s>
IBM	O
has	O
plans	O
to	O
add	O
a	O
considerable	O
number	O
of	O
new	O
probe	O
points	O
in	O
future	O
technology	O
level	O
releases	O
of	O
AIX	B-Application
6.1	O
and	O
in	O
the	O
next	O
major	O
AIX	B-Application
release	O
.	O
</s>
