This is a cross post to a cooperative-multitasking implementation that I did in the past and hosted on github >> matcha-threads <<.
Cooperative-multitasking allows to perform the thread scheduling in user space.
Executing threads need to give the control back to the scheduler such that
other threads can run. Since control is returned explicitly to the scheduler,
threads need to "cooperate".
The following code snippet shows an example of two such threads:
#include "lib/executor.h"
#include "lib/thread.h"
#include <cstdio>
void like_tea(nMatcha::Yielder& y) {
std::puts("like");
y.yield();
std::puts("tea");
}
int main() {
nMatcha::Executor e;
e.spawn(nMatcha::FnThread::make(like_tea));
e.spawn(nMatcha::FnThread::make([](nMatcha::Yielder& y) {
std::puts("I");
y.yield();
std::puts("green");
}));
e.run();
return 0;
}
Which gives the following output when being run:
I
like
green
tea
The main focus of that project was to understand the fundamental mechanism
underlying cooperative-multitasking and implement such a yield() function as
shown in the example above.
Looking at the final implementation, the yield function does the following:
yield:
1. function prologue
2. push callee-saved regs to current stack
3. swap stack pointers (current - new)
4. pop callee-saved regs from new stack
5. function epilogue & return
Implementations for different ISAs are available here: