ZeroMQ

Handling Errors and ETERM

ØMQ’s error handling philosophy is a mix of fail fast and resilience. Processes, we believe, should be as vulnerable as possible to internal errors, and as robust as possible against external attacks and errors. To give an analogy, a living cell will self-destruct if it detects a single internal error, yet it will resist attack from the outside by all means possible.

Assertions, which pepper the ØMQ code, are absolutely vital to robust code; they just have to be on the right side of the cellular wall. And there should be such a wall. If it is unclear whether a fault is internal or external, that is a design flaw to be fixed. In C/C++, assertions stop the application immediately with an error. In other languages, you may get exceptions or halts.

When ØMQ detects an external fault, it returns an error to the calling code. In some rare cases, it drops messages silently if there is no obvious strategy for recovering from the error.

In most of the C examples we’ve seen so far, there’s been no error handling. Real code should do error handling on every single ØMQ call. If you’re using a language binding other than C, the binding may handle errors for you. In C, you do need to do this yourself. There are some simple rules, starting with POSIX conventions:

• Methods that create objects return NULL if they fail.

• Methods that process data may return the number of bytes processed, or -1 on an error or failure.

• Other methods return 0 on success and -1 on an error or failure. ...