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[fiber] Add more concurrency classes #1026

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merged 11 commits into from
May 20, 2024

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salkinium
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@salkinium salkinium commented May 20, 2023

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.

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

@salkinium salkinium added this to the 2023q2 milestone May 20, 2023
@salkinium salkinium removed this from the 2023q2 milestone Jul 10, 2023
@salkinium salkinium force-pushed the feature/fiber_concurrency branch 2 times, most recently from 97c4cb4 to d9e13d0 Compare April 14, 2024 10:03
@salkinium salkinium added this to the 2024q2 milestone Apr 14, 2024
@salkinium salkinium force-pushed the feature/fiber_concurrency branch 3 times, most recently from 3526783 to 3f372b6 Compare April 14, 2024 21:19
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salkinium commented Apr 14, 2024

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.

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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.

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

@salkinium salkinium force-pushed the feature/fiber_concurrency branch 2 times, most recently from c8575fb to 377553c Compare April 20, 2024 16:44
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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 salkinium force-pushed the feature/fiber_concurrency branch 2 times, most recently from 0d3fa53 to 6803ce0 Compare April 21, 2024 16:01
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Very nice!

I haven't managed to look at all the synchronization primitives, but will do tomorrow.

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@salkinium salkinium force-pushed the feature/fiber_concurrency branch 8 times, most recently from d9b837a to 72ab66d Compare May 6, 2024 14:51
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@salkinium salkinium force-pushed the feature/fiber_concurrency branch 2 times, most recently from ae6328c to 407e1a6 Compare May 10, 2024 21:36
@salkinium salkinium marked this pull request as ready for review May 12, 2024 07:34
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@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.

@salkinium salkinium force-pushed the feature/fiber_concurrency branch 2 times, most recently from c067a44 to 1dea124 Compare May 12, 2024 11:35
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@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.

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chris-durand commented May 13, 2024

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

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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
 %% 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
 %% 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
 %% 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

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

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salkinium commented May 15, 2024

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!

@salkinium salkinium force-pushed the feature/fiber_concurrency branch 3 times, most recently from 13e0760 to 460bcee Compare May 20, 2024 17:10
@salkinium salkinium added the ci:hal Triggers the exhaustive HAL compile CI jobs label May 20, 2024
@salkinium salkinium merged commit 39a9f4d into modm-io:develop May 20, 2024
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@salkinium salkinium deleted the feature/fiber_concurrency branch September 17, 2024 10:05
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