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What does “Any CPU” really mean?

There’s a new “Prefer 32-bit” option in Visual Studio 2012 that tripped us up, and can trip you up too.

Running through some standard JNBridgePro test examples recently, we were surprised that the examples didn’t work, and the embedded Java side failed. The examples were created using Visual Studio 2012, set Any CPU, and, since we were running the tests on a 64-bit machine and were using shared memory, we supplied a 64-bit JRE as part of the configuration.

After a bit of investigation, we discovered a new setting in the VS 2012 project that isn’t in previous versions of Visual Studio: in the project’s properties, under the Build tab, there is a new checkbox: “Prefer 32-bit.” The checkbox only seems to be enabled when Any CPU is selected, and it was automatically checked. And indeed the running process was 32-bit. What was happening? Didn’t “Any CPU” mean that the application would run as 64 bit on a 64-bit system, and 32 bit on a 32-bit system? And how does “Any CPU/Prefer 32-bit” differ from simple x86?

We did some research and discovered an explanation in a Microsoft blog post here. It turns out that the meaning of “Any CPU” has changed a bit. I won’t go into too many details, but would suggest that anyone doing .NET development read the blog post. In a nutshell, the new “Prefer 32-bit” is connected to Microsoft’s new support for ARM architectures as of .NET 4.5. It also seems to have something to do with Microsoft’s retreat from encouraging 64-bit and “Any CPU” development in deference to 32-bit development, as the complexity of supporting both 32-bit and 64-bit environments has become apparent. In making the changes, Microsoft has made some design decisions that we feel are to the detriment of users. (Also note that we still strongly believe in supporting “Any CPU” and x64 development. Read more about the bitness challenge in this blog post.)

In the first design decision we take issue with, Microsoft has decided to make “Any CPU/Prefer 32-bit” the default in Visual Studio 2012 when creating .NET 4.5 applications. This is unfortunate because users assume “Any CPU” meant the same thing as it previously did (the application will run as 64 bit on 64-bit systems), and because the new “Prefer 32-bit” setting is somewhat hidden and not immediately obvious. In our experience, most users set the Target Platform (Any CPU/x86/x64/etc.) in the configuration manager, where there’s no mention of the “Prefer 32-bit” setting – “Prefer 32-bit” is only visible (and settable) in the project properties, where most developers don’t have a reason to look, but where it’s already been set, without telling the developer.

Second, setting “Prefer 32-bit” as the default leads to inconsistencies in creating new projects versus migrating exiting ones. “Prefer 32-bit” is set in new “Any CPU” projects created in VS 2012, but it isn’t set when migrating an existing project from VS 2010. Props to Microsoft for not altering the behavior of existing projects when migrating from VS 2010 to 2012, but why not go a step further and make “Any CPU” behavior consistent by leaving the “Prefer 32-bit” setting turned off by default in new projects created with VS 2012?

The inconsistent behavior is what really what makes this change so annoying. Microsoft could have offered the “Prefer 32-bit” capability and not surprise unsuspecting users by just leaving the setting turned off by default. Users would happily create new applications without problem, and without suspecting that “Any CPU” could possibly mean anything different than what it meant before. Interestingly enough, users could still target ARM platforms if “Any CPU” running on ARM was guaranteed to run as 32 bit (until 64-bit ARM chips become generally available, at which time such applications will run as 64 bit). Microsoft could also allow developers to specifically target ARM in the same way as they can now specifically target x86, x64, and IA64. I can almost guarantee that this would be less confusing than the current use of “Any CPU” and “Prefer 32-bit,” particularly since very few .NET developers are going to be targeting ARM, at least not for a long time.

So what does this mean for users of JNBridgePro and the JNBridge adapters? First, as mentioned earlier, we still strongly believe in “Any CPU” and x64 development, and are working hard to create products that can be used in “Any CPU” applications. There are some subtleties and complications in making this transparent to the user, but we’ve done a lot of work on this, which you can see in JNBridgePro 7.0, and will soon see in new releases of the adapters. We’ve discussed the work that we’ve done here. The next version of JNBridgePro will have even more support for “Any CPU” applications; particularly, when using shared memory, you’ll be able to specify paths to both a 32-bit and a 64-bit jvm.dll, and the proper JRE will be loaded depending on whether it’s a 32-bit or a 64-bit process. This will make Any CPU applications using shared memory even easier to deploy on any system without changes.

Second, we want all our users to know that JNBridgePro will still work in all “Any CPU” applications using shared memory, even when “Prefer 32-bit” is turned on. When it is, simply use a 32-bit JRE, and when it isn’t turned on, use a 32-bit or 64-bit JRE as is appropriate to the platform. The V.next of JNBridgePro, with the aforementioned ability to specify both 32-bit and 64-bit JREs, will make this process even more transparent.

We’re always trying to stay ahead of Microsoft’s changes, whether they’re ill-advised or not. The change to the meaning of “Any CPU,” and the new default “Prefer 32-bit” setting are just one example of how we’ve stayed on top of .NET’s evolution, so that your applications using JNBridgePro and the adapters continue to work despite the changes to .NET, and will continue to work in the future.

Software Development and the Bitness Challenge

Since 64-bit processors were introduced about ten years ago, they have become the default on both desktop and server machines. With a larger addressable process memory space, wider range of representable integers, and greater floating point precision, what’s not to like? For software developers that need to support both 32- and 64-bit machines, it’s a bit complicated.

Applications written in pure managed code (whether in .NET Intermediate Language or Java bytecodes)  will typically work just fine regardless of whether they’re running as 32-bit or 64-bit processes. However many applications also contain non-managed or native code that is targeted to a specific “bitness” (where “bitness” describes the distinction between 32-bit and 64-bit qualities of a platform, process, or system). In these cases, the developer needs to be careful that the right version of the non-managed code executes when the application is run, depending on the bitness of the running process. For software vendors, like JNBridge, which produce both self-contained applications and components that are integrated inside other users’ applications, the situation becomes even more tricky – the right version of the components needs to be included in the application, and it’s a common and easy mistake for users to include the components with the wrong bitness.  The user sees an error, and we get a support call. Better to reduce the chances of an error, and everybody will be happy.

After facing these issues for a number of years, we now have a workable solution, and our new JNBridgePro 7.0 release reflects this experience. We’d like to share what we’ve learned, so that other developers can successfully address the bitness challenge.

Create a single unified installer for both 32-bit and 64-bit scenarios. Developers’ first instinct is to create separate 32-bit and 64-bit builds and distribute separate installers for each. While this may seem logical, it leads to a lot of user confusion. In our experience, users faced with the decision as to whether to download the installer for the 32-bit or 64-bit version frequently download the wrong one. When they discover this error, they have to go back and download the other version, often after engaging support. Combining the 32- and 64-bit versions into a single installer is a win for the user and a win for us.

The challenge in building a single installer is that most installer generator packages either don’t allow 32-bit and 64-bit components to be combined in a single installer that would run on either system, or if they do support it, the resulting installation is too complicated. In particular, the usual technique of combining 32-bit and 64-bit installers, and a bootstrapper, into a single installer won’t work in our case, since we want 64-bit components to be installed on 32-bit machines, too. We resolved this by creating a single 32-bit installer (that is, one that would run on both 32-bit and 64-bit machines), and fooling the installer generator into thinking that the 64-bit components were simply “content,” so that the installer generator wouldn’t reject them. The “content” is all the 64-bit components packed into a single zip file. When the installer is run, a custom action extracts the 64-bit components then removes the zip file. While there are subtleties in getting this right (Google ‘advertised shortcut’ for pointers to issues that can arise), when done correctly this approach works perfectly and yields a single installer that runs on both 32-bit and 64-bit machines, and installs both 32-bit and 64-bit components on both machines. (Why do we need to install 64-bit components on 32-bit machines? Because, while the build machine may be 32-bit, the developer may be generating 64-bit applications.)

Ensure that users can use your components to create “Any CPU” applications. “Any CPU” applications are designed to automatically run as 32-bit processes on 32-bit machines and as 64-bit processes on 64-bit machines. This is very attractive as it allows the application to take advantage of whatever platform it runs on, and suggests that the code is portable. “Any CPU” implies that the code is completely managed, but there’s nothing to prevent unmanaged code, including third-party components, from being included. We’ve encountered scenarios where a developer used JNBridgePro to create an Any CPU application on their 64-bit development machine, successfully test it there, then ran into problems in deploying the application to a 32-bit machine. Situations like this suggest that developers should develop both 32-bit and 64-bit versions of their components or applications, but this is kicking the developer’s problem down the road, forcing the user to deal with using the right version. This should be as unacceptable to the software developer as it is to the user.

In order to allow users to create and run “Any CPU” applications, we changed JNBridgePro so that the appropriate 32-bit or 64-bit components would be loaded at run time depending on the bitness of the running process. However, platform vendors don’t make this easy. We discovered that the simplest way to test bitness at run time in .NET is to check the value returned by IntPtr.Size: 4 means you’re running as a 32-bit process; 8 means it’s a 64-bit process. (Note that the .NET alternative of calling Environment.Is64BitProcess won’t work in our case, since that API is only supported in .NET Framework 4.0 and later, and our components also need to be able to run in .NET Framework 2.0 through 3.5.) In Java, simply check the value of the system property os.arch. “x86” means that it’s a 32-bit process; “x86_64” means it’s a 64-bit process. These tests allow us to load the appropriate components at run-time, thereby supporting users who want to create applications that run anywhere, even though some of our components contain 32-bit or 64-bit targeted code.

Be careful using the Windows registry. When Microsoft created 64-bit Windows, they made the fateful decision to provide separate 32-bit and 64-bit registries, accessible only to respective 32-bit and 64-bit processes. The problem arises when the registry is used to share information between applications. Information deposited by  a 32-bit application is inaccessible to a 64-bit application, and vice versa. The answer is to only use the registry for information used by a single application, and only when the application’s bitness on that machine will always be the same. Save the information shared between applications in files; do not use the registry. JNBridge used to store information in the registry, but this became a constant source of support headaches once 64-bit platforms were introduced. Now that we store information in files, not the registry, these bitness-related headaches have gone away.

In conclusion: If all the processes in the world were 64-bit processes, the problems I’ve mentioned above wouldn’t exist.  However, as long as 32-bit processes and platforms still exist and must be supported, software developers must be careful and watch out for pitfalls that can trip up users. When developers adhere to the guidelines discussed above, users’ bitness problems should disappear, to the great benefit of both users and software support teams.