What is FEATURE_PAL compiler directive means in .net 4 source code

Question

I am having problem with understanding what FEATURE_PAL compiler directive means in .net 4.0 source code. It is used almost in every class that access unmanaged code.

Answer 1

PAL = Platform Adaptation Layer. It is first and foremost a detail of the CLR, insulating it from the operating system implementation. You'll indeed see it used in the Reference Source copy of the source code for the .NET 4 classes. It appears in any code that has a strong dependency on the underlying operating system implementation, bypassing such code since it cannot work on an operating system other than Windows.

Answer 2

You may be familiar with the use of the DEBUG and RELEASE directives to wrap blocks of code specific for testing/production code.

The .NET 4.0 framework uses the FEATURE_PAL compiler directive to execute code on newer platforms. It has to adapt to the platform by calling native methods found in native dlls. Hence the name of the feature: 'Platform adaptation layer'.

I came across this post after looking at the code for the Process class. One can image that killing a process works different on a given platform.

Think of the your code running on a newer version of Windows installed on a device that uses an ARM processor. When killing a process you need to call a method inside a native dll tailored to that platform.

So when compiling the framework for such platforms the FEATURE_PAL compiler directive is set as 'conditional compilation symbol'.