[fiber] Add more concurrency classes

[salkinium]

Fibers need a standard set of efficient constructs. I modelled these classes after the C++ thread concurrency interfaces. Not sure if useful, but also probably not really much room for improvement anyways.

• [x] https://github.com/modm-io/avr-libstdcpp/pull/35
• [x] modm::fiber::sleep -> modm::this_fiber::sleep_for
• [x] modm::this_fiber::sleep_until
• [x] modm::this_fiber::get_id
• [x] Align modm::fiber::Task to std::jthread interface, incl. stop_token.
• [x] stop_token and stop_source (simplified)
• [x] mutex
• [x] timed_mutex
• [x] recursive_mutex
• [x] recursive_timed_mutex
• [x] counting_semaphore (=binary_semaphore)
• [x] shared_mutex
• [x] shared_timed_mutex
• [x] once_flag
• [x] call_once
• [x] latch
• [x] barrier
• [x] condition_variable
• [x] unit tests
• [x] More documentation
• [x] Hardware testing
  • [x] STM32F723
  • [x] STM32G071
  • [x] ATmega2650

[salkinium]

It's still missing unit tests for latch, barrier and condition_variable and a bunch of documentation, however, it would be amazing if this could get reviewed with a special focus on C++ "conformity". This implementation should be interrupt-safe (when it makes sense for the functions), so that we can use then in the HAL as signalling primitives for operation completions in the future.

I also noticed that avrlibstd++ does not have <atomic>, I assume it was really annoying to port, @chris-durand? If it's an issue with the builtin gcc atomics not being implemented for avr-gcc, we can reuse the Cortex-M0 ones now.

[chris-durand]

I also noticed that avrlibstd++ does not have <atomic>, I assume it was really annoying to port, @chris-durand? If it's an issue with the builtin gcc atomics not being implemented for avr-gcc, we can reuse the Cortex-M0 ones now.

I haven't tried to be honest but I expect that the same solution as for Cortex-M0 will work. The header is mostly implemented using compiler builtins. I'd expect it to fall back to calling a library function in case the operation is not atomic on AVR. If you are lucky just dropping in the headers and compiling atomics_c11_cortex.cpp.in for AVR could be sufficient.

C++20 atomic wait which requires OS support shouldn't be an issue because it is only enabled when _GLIBCXX_HAS_GTHREADS is set.

[chris-durand]

I'll take a look at the PR over the weekend.

[salkinium]

If you are lucky just dropping in the headers and compiling atomics_c11_cortex.cpp.in for AVR could be sufficient.

Yup that just works, thanks!

[salkinium]

@chris-durand, I added ARMv8-M stack protection, could you check if the example/generic/fiber still works? I don't have a Cortex-M33 in my collection.

[chris-durand]

@chris-durand, I added ARMv8-M stack protection, could you check if the example/generic/fiber still works? I don't have a Cortex-M33 in my collection.

When running this on an STM32L5 I get a hardfault. The stack overflow bit (STKOF, bit 4) in UFSR is set. The fault happens inside modm_context_jump, triggered from the call to yield() inside the lambda of fiber_y1.

[chris-durand]

Let me know if there is something specific I can check.

[chris-durand]

Listing: https://gist.github.com/chris-durand/4f3deae41aacbfd0cad2c9d067df0b5a

[salkinium]

Hm, so setting MSPLIM is no problem, setting PSPLIM once on context_start is no problem either, but then on the first context switch it fails? ugh.

Could you try to change the assembly in context_jump?

1. %% elif with_psplim
   -       "ldm r1, {r1-r2}    \n\t"
   -       "mov sp,  r1        \n\t"   // Set PSP to ctx->sp
   -       "msr psplim, r2     \n\t"   // Set PSPLIM to ctx->bottom
   +       "ldm r1, {r2-r3}    \n\t"
   +       "mov sp,  r2        \n\t"   // Set PSP to ctx->sp
   +       "msr psplim, r3     \n\t"   // Set PSPLIM to ctx->bottom
   %% else

2. %% elif with_psplim
   -       "ldm r1, {r1-r2}    \n\t"
   -       "mov sp,  r1        \n\t"   // Set PSP to ctx->sp
   -       "msr psplim, r2     \n\t"   // Set PSPLIM to ctx->bottom
   +       "ldr sp, [r1]       \n\t"   // Set PSP to ctx->sp
   +       "ldr r2, [r1, #4]   \n\t"
   +       "msr psplim, r2     \n\t"   // Set PSPLIM to ctx->bottom
   %% else

3. %% elif with_psplim
   -       "ldm r1, {r1-r2}    \n\t"
   -       "mov sp,  r1        \n\t"   // Set PSP to ctx->sp
   -       "msr psplim, r2     \n\t"   // Set PSPLIM to ctx->bottom
   +       "ldm r1, {r2-r3}    \n\t"
   +       "msr psplim, r3     \n\t"   // Set PSPLIM to ctx->bottom
   +       "mov sp,  r2        \n\t"   // Set PSP to ctx->sp
   %% else

4. %% elif with_psplim
   -       "ldm r1, {r1-r2}    \n\t"
   -       "mov sp,  r1        \n\t"   // Set PSP to ctx->sp
   -       "msr psplim, r2     \n\t"   // Set PSPLIM to ctx->bottom
   +       "ldr r2, [r1, #4]   \n\t"
   +       "msr psplim, r2     \n\t"   // Set PSPLIM to ctx->bottom
   +       "ldr sp, [r1]       \n\t"   // Set PSP to ctx->sp
   %% else

[chris-durand]

No success with any of the options. I've also tried replacing the code in both context_start and context_jump.

[salkinium]

Ok, then I'll descope it for now and will order a bunch of new development boards and debug it some more. Thanks for your help!