diff --git a/docs/CODING_STYLE.md b/docs/CODING_STYLE.md index 9b2fd5cc84..d945f8cdbe 100644 --- a/docs/CODING_STYLE.md +++ b/docs/CODING_STYLE.md @@ -55,53 +55,49 @@ title: Coding Style - Do not write `foo ()`, write `foo()`. -## Other +## Code Organization and Semantics - Please name structures in `PascalCase` (with exceptions, such as public API structs), variables and functions in `snake_case`. -- Avoid static variables, except for caches and very few other - cases. Think about thread-safety! While most of our code is never - used in threaded environments, at least the library code should make - sure it works correctly in them. Instead of doing a lot of locking - for that, we tend to prefer using TLS to do per-thread caching (which - only works for small, fixed-size cache objects), or we disable - caching for any thread that is not the main thread. Use - `is_main_thread()` to detect whether the calling thread is the main - thread. +- Avoid static variables, except for caches and very few other cases. Think + about thread-safety! While most of our code is never used in threaded + environments, at least the library code should make sure it works correctly + in them. Instead of doing a lot of locking for that, we tend to prefer using + TLS to do per-thread caching (which only works for small, fixed-size cache + objects), or we disable caching for any thread that is not the main + thread. Use `is_main_thread()` to detect whether the calling thread is the + main thread. - Do not write functions that clobber call-by-reference variables on - failure. Use temporary variables for these cases and change the - passed in variables only on success. + failure. Use temporary variables for these cases and change the passed in + variables only on success. - The order in which header files are included doesn't matter too - much. systemd-internal headers must not rely on an include order, so - it is safe to include them in any order possible. - However, to not clutter global includes, and to make sure internal - definitions will not affect global headers, please always include the - headers of external components first (these are all headers enclosed - in <>), followed by our own exported headers (usually everything - that's prefixed by `sd-`), and then followed by internal headers. - Furthermore, in all three groups, order all includes alphabetically + much. systemd-internal headers must not rely on an include order, so it is + safe to include them in any order possible. However, to not clutter global + includes, and to make sure internal definitions will not affect global + headers, please always include the headers of external components first + (these are all headers enclosed in <>), followed by our own exported headers + (usually everything that's prefixed by `sd-`), and then followed by internal + headers. Furthermore, in all three groups, order all includes alphabetically so duplicate includes can easily be detected. -- Please avoid using global variables as much as you can. And if you - do use them make sure they are static at least, instead of - exported. Especially in library-like code it is important to avoid - global variables. Why are global variables bad? They usually hinder - generic reusability of code (since they break in threaded programs, - and usually would require locking there), and as the code using them - has side-effects make programs non-transparent. That said, there are - many cases where they explicitly make a lot of sense, and are OK to - use. For example, the log level and target in `log.c` is stored in a - global variable, and that's OK and probably expected by most. Also - in many cases we cache data in global variables. If you add more - caches like this, please be careful however, and think about - threading. Only use static variables if you are sure that - thread-safety doesn't matter in your case. Alternatively, consider - using TLS, which is pretty easy to use with gcc's `thread_local` - concept. It's also OK to store data that is inherently global in - global variables, for example data parsed from command lines, see +- Please avoid using global variables as much as you can. And if you do use + them make sure they are static at least, instead of exported. Especially in + library-like code it is important to avoid global variables. Why are global + variables bad? They usually hinder generic reusability of code (since they + break in threaded programs, and usually would require locking there), and as + the code using them has side-effects make programs non-transparent. That + said, there are many cases where they explicitly make a lot of sense, and are + OK to use. For example, the log level and target in `log.c` is stored in a + global variable, and that's OK and probably expected by most. Also in many + cases we cache data in global variables. If you add more caches like this, + please be careful however, and think about threading. Only use static + variables if you are sure that thread-safety doesn't matter in your + case. Alternatively, consider using TLS, which is pretty easy to use with + gcc's `thread_local` concept. It's also OK to store data that is inherently + global in global variables, for example data parsed from command lines, see below. - You might wonder what kind of common code belongs in `src/shared/` and what