Current software projects deal with exceptions in implementation and maintenance phases without a clear definition of exception handling policies. We call an exception handling policy the set of design decisions that govern the use of exceptions in a software project. Without an explicit exception handling policy, developers can remain unaware of the originally intended use of exceptions. In this paper, we present Exception Handling Policies Language (EPL), a domain-specific language to specify and verify exception handling policies. The evaluation of EPL was based on a user-centric observational study and case studies. The user-centric study was performed to observe how potential users of the language actually use it. With this study, we could better understand the trade-offs related to different language design decisions based on concrete and well-documented observations and experiences reported by participants. We identified some language characteristics that hindered its use and that motivated new language constructs. In addition, we performed case studies with one open-source project and two industry-strength systems to investigate how specifying and verifying exception handling policies may assist in detecting exception handling problems. The results show that violations of exception handling policies help to indicate potential faults in the exception handling code.

Exception handling mechanisms have been introduced into programming languages in an effort to help deal with runtime irregularities. These mechanisms aim to improve code reliability by providing constructs for sectioning code into exception scopes (e.g. Java try blocks) and exception handlers (e.g. Java catch blocks). Whilst exception handling mechanisms have been the focus of much research over the past years, empirical studies have only focused on characterising exception handling code of Java and C# programs. There exists little empirical evidence on how exception handling mechanisms are used to develop software with other programming languages. Moreover, to date there exists no empirical study which has examined the structure of exception scopes across software projects. We address these shortcomings by examining the commonalities and differences of both exception scopes and handlers implemented with a wider range of languages. To this end, we analysed 50 software projects, containing code developed in C++, JavaScript, PHP, Java and C#. More than 9 million lines of code and over 20,000 exceptional code blocks were analysed. Our findings revealed significant differences in the frequency, structure and length of exception scopes and exception handlers across languages. This finding suggests that certain exception handling mechanisms are less explored by programmers using certain programming languages. However, regardless of language, exception handlers remained simplistic and in general only ever one handler was associated with each scope. Finally, our analysis confirms the existing belief that developers often pay little attention to developing exception scoping and handling behaviour.