This chapter covers
- How exceptions work with asynchronous code
- How to fix lost exceptions
- Handling exceptions in async void methods
In this chapter, we are going to talk about exceptions. We’ll discuss how they work in asynchronous code and the differences in how they work in non-asynchronous code. In transitional code, exceptions bubble up the call stack. As we’ve seen in chapters 3, 5, and 11, in asynchronous code, callbacks are constantly registered to be called later, often from other threads; thus, the call stack no longer describes the flow of your code. This knowledge and the knowledge about what async/await does to mitigate this are important when debugging problems related to exceptions in asynchronous code, that is, when debugging any situation where the asynchronous code fails in a non-straightforward way. We’ll also cover some pitfalls you should be aware of regarding exceptions.
12.1 Exceptions and asynchronous code
Exceptions use the call stack. The call stack is a data structure (specifically a stack) used by the system to implement the concept of methods (or functions or procedures, depending on your programming language). When you call a method, the system pushes the memory address of the next instruction into the call stack, and when you execute a return statement, the system jumps to the address at the top of the stack (this explanation is a gross oversimplification because this book is not about processor architecture).