Synchronize with all calls to unpark in id-based thread parker

[joboet]

The documentation for thread::park guarantees that "park synchronizes-with all prior unpark operations". In the id-based thread parking implementation, this is not implemented correctly, as the state variable is reset with a simple store, so there will not be a synchronizes-with edge if an unpark happens just before the reset. This PR corrects this, replacing the load-check-reset sequence with a single compare_exchange.

[rustbot]

r? @thomcc

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[thomcc]

@bors r+

[bors]

📌 Commit fd9fcc5 has been approved by thomcc

It is now in the queue for this repository.

[bors]

⌛ Testing commit fd9fcc5 with merge d06ca0f...

[bors]

☀️ Test successful - checks-actions
Approved by: thomcc
Pushing d06ca0f to master...

[rust-timer]

Finished benchmarking commit (d06ca0f): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.9%	[2.9%, 4.5%]	3
Regressions ❌ (secondary)	3.3%	[2.0%, 5.2%]	3
Improvements ✅ (primary)	-4.3%	[-4.3%, -4.3%]	1
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	1.9%	[-4.3%, 4.5%]	4

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 632.907s -> 633.508s (0.09%)
Artifact size: 347.12 MiB -> 347.19 MiB (0.02%)