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What is "MercutioHUnlockPatch" and why does RC install it?


(Tech0011A -- 03/11/98)

MercutioHUnlockPatch is a "free" system exension by Brian Zuk which is installed by theRAM Charger installer to fix a common problem that crashes many Macintoshes.

What is the problem?

Many popular Macintosh applications incorporate a "canned" package of software, known as Mercutio MDEF, that allows developers to easily and elegantly extend the power of their application menus. It was discovered applications that use pre-version 1.5 of this package were crashing systems as a result of a bug in Mercutio MDEF. Although this problem has surfaced because of a bug in the Mercutio MDEF package, Apple reports that there are other (non-Mercutio) applications, and even parts of the OS, that can cause the crash.

Does this effect my system?

Yes. As far as we know, this effects all systems if you happen to be running an application using pre -version 1.5 Mercutio MDEF, and other software may cause the problem as well. Also, Apple currently claims that will not put a fix in the system (see below). Since we do not know the list of applications which are dangerous, we recommend everyone run the patch which is basically painless.

What is the fix?

A number of "free" system extensions have been developed by generous programmers that will fix the problem. Any one of these added in your extensions folder will avoid the problem. In specific, we have chosen MercutioHUnlockPatch as the extension we prefer. Since no drawbacks are known, the RAM Charger installer puts MercutioHUnlockPatch in your system (if a more recent version is not already installed).

Why might the RAM Charger installer warn me?

If you already have another known "Mercutio" fix extension installed, then the RAM Charger installer will let you know - since having multiple fixes is a waste. As far as we know, there is no problem having multiple fixes installed. However, that would be extra overhead. If you are warned, you might wish to take the opportunity to disable one of the fixes.

What does Apple have to say about this?

In the Apple tn1118.html, they write:

All users, including developers, should consider installing a system extension which Apple will soon release to address this problem. This extension will protect you from symptoms which result from code which you cannot fix until revised applications appear which do not have the problem. You will be able to obtain this extension, along with further details, from another web page. We'll post a specific reference here as soon as it becomes available. [as far as we know, none is availabe from Apple yet, only from random generous developer -jump]

Apple does not currently plan to roll this functionality into Mac OS. This is because the problem warrants fixing for more than just the next version of Mac OS. (The extension has been qualified under Mac OS 7.6 and later.) Another reason this fix will not be rolled into the system is that it would require the Memory Manager to have intimate knowledge of QuickDraw, and minimizing this kind of coupling is in everyone's long-term best interest. A future version of Mac OS will include a work-around for the most common crash case (NQDStdText).

Developers should not rely on the presence of the functionality provided by this extension. DTS and Evangelism are investigating licensing this extension to developers for redistribution. We'll post an announcement and update this Technote when we resolve all the issues.


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