It's my same argument that there should be no maximum number of lines to a function. Sometimes, you just need to do a lot of work. I comment the code blocks, maybe with steps/parts, but there's no point in making a function that's only called in one place.
But anything is better than one person I met who somehow was programming without knowing how to define their own functions. Gross
There's nothing wrong with doing that if it helps make your code clearer. The compiler's optimizer will inline it when appropriate so there's no runtime overhead either.
I encourage junior developers that get into this habit (getting worse now, with LLMs) to convert the comment into a function name and add the block as a function, thinking pretty carefully about its function signature. If you have a `typedef struct state` that gets passed around, great.
The reason for splitting up this code is so that the person writing it doesn't fuck up, the input/output is expressed as types and validated before they push it. It's easy for me to review, because I can understand small chunks of code better than big chunks, and logically divides up the high level architecture from the actual implementation so I can avoid reviewing the latter if I find trouble with the former. It's also good as a workflow, where you can pair to write out the high level flow and then split off to work on implementation internally. And most importantly, it makes it possible to test the code.
I have had this discussion with many grumbly developers that think of the above as a "skill issue." I don't really want to work with those people, because their code sucks.
[1] https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html
Small text sizes? What is the problem for you?
That tends to just make the project eventually implement an approximation of one... as what appears to have happened here.
How I'd solve the given problem is by using the PWM peripheral (or timer interrupts if no PWM peripheral exists) and pin change interrupts, with the CPU halted nearly 100% of the time. I suspect that approach is even simpler than what's shown here.
typedef struct blinky_state {
size_t pc;
uint64_t timer;
... variables that need to live across YIELDs ...
} blinky_state_t;
blinky_state_t blinky_state;
#define YIELD() s->pc = __LINE__; return; case __LINE__:;
void blinky(void) {
blinky_state_t *s = &blinky_state;
uint64_t now = get_ticks();
switch(s->pc) {
while(true) {
turn_on_LED();
s->timer = now;
while( now - s->timer < 1000 ) { YIELD(); }
turn_off_LED();
s->timer = now;
while( now - s->timer < 1000 ) { YIELD(); }
}
}
}
#undef YIELD
Your company is probably using hardware containing code I've written like this.
What's especially nice that I miss in other languages with async/await is ability to mix declarative and procedural code. Code you write before the switch(s->pc) statement gets run on every call to the function. Can put code you want to be declarative, like updating "now" in the code above, or if I have streaming code it's a great place to copy data.
If there is just one instance of a co-routine, which is often the case for embedded software, one could also make use of static variables inside the function. This also makes the code slightly faster.
You need some logic, if for example two co-routines need to access a shared peripheral, such as I2C. Than you might also need to implement a queue. Last year, I worked a bit on a tiny cooperative polling OS, including a transpiler. I did not finish the project, because it was considered too advanced for the project I wanted to use it for. Instead old fashion state machines documented with flow-charts were required. Because everyone can read those, is the argument. I feel that the implementation of state machines is error prone, because it is basically implementing goto statements where the state is like the label. Nasty bugs are easily introduced if you forget a break statement at the right place is my experience.
Agreed re: making the state a static variable inside the function. Great for simple coroutines. I made it a pointer in the example for two reasons:
- Demonstrates access to the state variables with very little visual noise... "s->"
- For sub-coroutines that can be called from multiple places such as "delay" you make the state variable the first argument. The caller's state contains the sub-coroutine's state and the caller passes it to the sub-coroutine. The top level coroutine's state ends up becoming "the stack" allocated at compile-time.
I’m not sure this is so much hacking as an accepted technique from the old-old days which has somewhat fallen out of favour, especially as C is falling a little outside of the mainstream these days.
Perhaps it’s almost becoming lost knowledge :)
It's using Simon Tatham's method based on Duff's device (https://www.chiark.greenend.org.uk/~sgtatham/coroutines.html)
mikepurvis•6h ago
That said, if I was stuck rolling this myself, I think I’d prefer to try to do it with “real” codegen than macros. If nothing else it would give the ability to do things like blocks and correctness checks, and you’d get much more readable resulting source when it came to stepping through it with a debugger.