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44 CHAPTER 30 Extending ColdFusion with CFX

If the CFX Tag Works with Files

If the guts of the CFX tag are thread-safe, but you are asking the tag to do something like create or

manipulate a ﬁle on the server’s drive, then you might want to lock access to the ﬁle, rather than to

the tag itself. The

<cflock> tags would still surround the CFX tag in your ColdFusion code, but

you would most likely use the complete ﬁlename as the

NAME of the lock, rather than the tag. If the

tag is merely reading the ﬁle, you could use

type=”ReadOnly”; if the tag might be creating or chang-

ing the ﬁle, you would have to use

type=”Exclusive”.

You would also want to surround other portions of your CFML code that access the same ﬁle—

regardless of whether they involve CFX tags—with

<cflock> tags. The <cflock> tags should have

the same

name as the ones around the CFX tag itself, and should use type=”Exclusive” for creation

or modiﬁcations and

type=”ReadOnly” if merely reading the ﬁle.

Keeping the Page Itself in Mind

It’s worth noting that just because a tag is thread-safe internally, that doesn’t automatically mean

that a ColdFusion page’s use of the tag is thread-safe. For instance, if you were supplying

APPLICA-

TION

or SESSION variables to the various attributes of a CFX tag, or if you were asking the CFX tag

to set variables in the

APPLICATION or SESSION scope, then it is theoretically possible for a logical “race

condition” problem to occur if one page request changes those variables at the same time, perhaps

resulting in some kind of data loss or logical data corruption. If the nature of your application is

such that this could be a problem (and only you can determine that), you should continue to lock.

NOTE

As you probably already know, the need for locking dramatically decreased as of ColdFusion MX. That doesn’t change the fact that

any access to shared resources in CFML pages—whether dealing with CFX tags or not—must be locked if the nature of the application

logic (that means your stuff, not ColdFusion’s internals) is such that problems could arise if multiple threads execute the code at the

same time. For more details on this topic, see the “Introducing the Web Application Framework” chapter in our companion volume,

The Macromedia ColdFusion MX 7 Web Application Construction Kit (Macromedia Press).

Using CFX Tags with Previous Versions of ColdFusion

CFX tags are not something that can only be used with current versions of ColdFusion. The CFX

API was actually the means of extending the server introduced ﬁrst in the product’s history, predat-

ing CFML custom tags, user-deﬁned functions, and CFCs.

CFX tags written with C++ can be used with any version of the product after (drumroll, please)

ColdFusion 2.0.

CFX tags written with Java can be used with ColdFusion 4.5 or later without any additional soft-

ware. You can use Java CFX tags with version 4.0 using the

<CFX_J> add-on package, which was

freely available from Macromedia’s Web site as of this writing.

Of course, the exception to this rule is the newfound ability for CFX tags to return structures to

ColdFusion pages (which was ﬁrst introduced in ColdFusion MX). See the “Returning Structures

from CFX Tags” section earlier in this chapter for details.

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