Structured Exception Handling

Chapter 11

Structured Exception Handling

Usually the exception handling model of a programming language is considered the domain of that particular language’s runtime. Under the hood, each language has its own way of detecting exceptions and locating an appropriate exception handler. Some languages perform exception handling completely within the language runtime, whereas others rely on the structured exception handling (SEH) mechanism provided by the operating system—which in our case is Win32.

In the world of managed code, exception handling is a fundamental feature of the common language runtime execution engine. The execution engine is fully capable of handling exceptions without regard to language, allowing exceptions to be raised in one language and caught in another. At that, the runtime does not dictate any particular syntax for handling exceptions. The exception mechanism is language-neutral in that it is equally efficient for all languages.

No special metadata is captured for exceptions other than the metadata for the exception classes themselves. No association exists between a method of a class and the exceptions that the method might throw. Any method is permitted to throw any exception at any time.

Although we talk about managed exceptions thrown and caught within managed code, a common scenario involves a mix of both managed and unmanaged code. Execution threads routinely traverse managed and unmanaged blocks of code through the use of the common language runtime’s platform invocation mechanism (P/Invoke) and other interoperability mechanisms. (See Chapter 15, “Managed and Unmanaged Code Interoperation.”) Consequently, during execution, exceptions can be thrown or caught in either managed or unmanaged code.

The runtime exception handling mechanism integrates seamlessly with the Win32 SEH mechanism so that exceptions can be thrown and caught within and between the two exception handling systems.