las3_pub / predictable_parallel_patterns

Merge continuation-style into master branch

See merge request !13

Our benchmarks require isolation from other system effects. Additionally,
we would like to have a system with 'very symmetric cores' (no hyperthreading,
no different memory connections, ....) that falls more into  the embedded
class of devices than desktop processors do. The notes describe how to setup
an banana pi m3 with a linux distri with rt preemt patch to achieve this.

Tsan needs the fix for not leaking fibers on the server to work properly.
Disable the tests until we can somehow easily get a build of it on the CI server.

I am not sure if this is appropriate, but it works and is no focus of this project.

Make sure that the guard page leads to sigsegv as expected.

It is now possible to use a memory mapped stack that throws a SIGSEV if thes coroutine stacks are exhausted.

Remove the strict static memory allocation scheme in favour of placing objects on the heap at startup. This still keeps the requirements posed for modern, high performance embedded systems, but makes APIs a lot cleaner.

The cas size could exceed an unsigned long, so we use the correct cas_integer type for the traded_cas_field representations.

We fixed the bug in tsan causing it to crash after creating/deleting many fibers, because of that there is no need for this cache mechanism (you have to use the most recent clang build with the patch for it to work thought).

We yield after num_thread failed steals in a row. This parameter can be tuned for better performance, but we stick to a sensible default just to prevent massive spinning.

Tsan does not cope well with rapidely destroyed/created fibers. As it is currently too much effort to fully investigate the tsan issue we work around it by caching the shourt lived fibers based on their stack base address. This allows us to use thread sanitizer for now.

Older CMAKE versions wont work with export targets in different directories. For now we simply add the context_switcher manually to the export target of pls.

We still see very sporadic crashes, however the current version is at least a starting point for refactoring and debugging. Next steps have to be to re-enable tooling support (i.e. add code to let sanitizers do their work).

The current version has race conditions and is hard to debug (especially because of the fibers, if a wrong thread executes on a fiber we get segfalts very fast). To combat this mess we now refactor the code bit by bit while also adding tests where it can be done with reasonably effort).