I will leave it to others to point to the entire chapters in
the
documentation that discusses these issues as well as
innumerable blogs,
white papers and discussion lists and give the 10 second
rundown.
Normal HTTP request-response are stateless. No data is
persisted from
one request to the next under normal conditions. To allow
data to
persist ColdFusion (and most other web languages in one way
or another)
create persistent scopes. ColdFusion offers several levels
and varietes
of scopes to persist data; server, application, session,
client and
cookie to name some and request sort of in a way.
Each of these scopes of different purposes and
characteristics. Some
are specific to a user (session and client) some to an
application
(application) and some to an entire server (server). Some are
stored in
memory on the server (session, application and server) some
on the
client either in memory or a file (cookie).
Locking is a concept to protect data from race conditions.
Since web
applications can be accessed by multiple people from multiple
locations
at the same time, sometimes applications can attempt to
change the data
in a common variable to different values at the same time.
Sometimes
this can cause serious consequences to an application, i.e a
race
condition. When this is the case, locking can be employed to
only allow
the value of a variable to be changed one at a time, but this
can have
serious performance consequences so adjudication needs to be
used on
when and how much should be locked at any given point. In
versions past
(pre-CF5) there where bugs and problems with the global
scopes like
server, application and session so universal locking with was
a
workaround to avoid these problems.
Ok, that took way more then 10 seconds. You can see this is a
big
topic. If you are a beginner who wishes to learn more, I
highly
recomened reading the documentation and other published
material. Then
if you have specific questions about certain aspects of what
you read we
can help clarify the concepts.
Usually such broad and global questions do not receive much
positive
responses from a list such as this.
