Add multi-producer, multi-consumer channel (mpmc)

[obeis]

Closes #125712

Tracking issue: #126840

r? m-ou-se

[jeffparsons]

This module is not currently exposed publicly

No longer true as of this PR? :)

[obeis]

r? @Amanieu

[bors]

☔ The latest upstream changes (presumably #125443) made this pull request unmergeable. Please resolve the merge conflicts.

[Amanieu]

@bors r+

[bors]

📌 Commit 041e76b has been approved by Amanieu

It is now in the queue for this repository.

[bors]

⌛ Testing commit 041e76b with merge 8dd5cd0...

[bors]

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing 8dd5cd0 to master...

[rust-timer]

Finished benchmarking commit (8dd5cd0): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.3%	[0.3%, 0.3%]	1
Regressions ❌ (secondary)	0.2%	[0.2%, 0.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[0.3%, 0.3%]	1

Max RSS (memory usage)

Results (primary -1.1%, secondary 2.1%)

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)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.1%	[-1.1%, -1.1%]	1

Cycles

Results (primary -3.3%)

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)	0.9%	[0.9%, 0.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-7.5%	[-7.5%, -7.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-3.3%	[-7.5%, 0.9%]	2

Binary size

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

Bootstrap: 771.847s -> 770.002s (-0.24%)
Artifact size: 341.40 MiB -> 341.49 MiB (0.03%)