Compact process supervision

[SandroMaglione]

Summary

• replace five persistent process-termination Deferreds and nested races with one arbitration signal plus the existing join completion
• run the machine worker and a single supervisor as siblings so stop and failure reserve state, interrupt worker finalizers, and terminalize in one ordered path
• preserve initialization self-stop, concurrent stop/completion/failure, frozen terminal snapshots, and external failure cleanup semantics
• add focused external-failure lifecycle coverage and a patch changeset

Changeset

• Added or updated for a library or package-metadata change
• Not required because this PR does not change src/ or package.json

Validation

• pnpm check
• Relevant example checks, when examples changed
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed
• Reviewed the automated runtime-performance report, when runtime behavior changed

Three paired full local benchmark runs against the exact parent commit showed median memory changes of -27.8% for a raw managed process, -22.8% for an idle machine, -23.2% for two independent machines, -13.5% for a parent-child pair, and -12.0% for an observed parent-child pair. Machine and family lifecycle throughput improved by 5.9% and 4.4%; steady-state throughput remained neutral within run-to-run drift.

[github-actions]

Type performance

Measured with TypeScript 6.0.3 and skipLibCheck=true.

Scenario	Base	PR	Difference
Effect only	55	55	0 (0.0%)
Import effect-machine	55	55	0 (0.0%)
Machine.defineStates (3 states)	2,965	2,965	0 (0.0%)
Machine.make (3 states, 2 events)	8,715	8,715	0 (0.0%)
machine.handle (3 states, 2 transitions)	23,492	23,492	0 (0.0%)
machine.handle (depth 8)	117,075	117,075	0 (0.0%)
machine.handle (depth 12)	129,713	129,713	0 (0.0%)
machine.handle (depth 16)	145,055	145,055	0 (0.0%)
machine.handle (depth 24)	183,851	183,851	0 (0.0%)
machine.handle (wide depth 16)	214,189	214,189	0 (0.0%)
machine.handle (parallel/history/choice)	132,667	132,667	0 (0.0%)
machine.handle (4 successive calls)	128,674	128,674	0 (0.0%)
machine exact input/output/error/services	110,584	110,584	0 (0.0%)
execution adapter readiness	127,854	127,854	0 (0.0%)

Marginal instantiations are measured against the matching setup without that API call:

Scenario	Base	PR	Difference
Import effect-machine	0	0	0
Machine.defineStates (3 states)	2,910	2,910	0 (0.0%)
Machine.make (3 states, 2 events)	5,742	5,742	0 (0.0%)
machine.handle (3 states, 2 transitions)	14,777	14,777	0 (0.0%)
machine.handle (depth 8)	109,601	109,601	0 (0.0%)
machine.handle (depth 12)	121,039	121,039	0 (0.0%)
machine.handle (depth 16)	135,181	135,181	0 (0.0%)
machine.handle (depth 24)	171,577	171,577	0 (0.0%)
machine.handle (wide depth 16)	202,224	202,224	0 (0.0%)
machine.handle (parallel/history/choice)	114,331	114,331	0 (0.0%)
machine.handle (4 successive calls)	113,703	113,703	0 (0.0%)
machine exact input/output/error/services	100,670	100,670	0 (0.0%)
execution adapter readiness	102,092	102,092	0 (0.0%)

Check times (informational)

Scenario	Base	PR
Effect only	0.02s	0.02s
Import effect-machine	0.02s	0.02s
Machine.defineStates (3 states)	0.07s	0.07s
Machine.make (3 states, 2 events)	0.11s	0.11s
machine.handle (3 states, 2 transitions)	0.15s	0.17s
machine.handle (depth 8)	0.38s	0.34s
machine.handle (depth 12)	0.39s	0.39s
machine.handle (depth 16)	0.39s	0.40s
machine.handle (depth 24)	0.46s	0.45s
machine.handle (wide depth 16)	0.50s	0.48s
machine.handle (parallel/history/choice)	0.43s	0.40s
machine.handle (4 successive calls)	0.38s	0.39s
machine exact input/output/error/services	0.35s	0.35s
execution adapter readiness	0.43s	0.38s

Type instantiations are the comparison metric. Check time varies with runner load and is informational only.

[github-actions]

Runtime performance

Median of 5 independent benchmark processes on AMD EPYC 7763 64-Core Processor with Node v24.18.0.

Pull request baseline

Scenario	Effect Machine	XState 5	XState 6 alpha
Plan counter transitions	106,359 transitions/s	132,796 transitions/s	123,584 transitions/s
Drain burst with terminal fence	56,176 increments/s	400,195 increments/s	112,669 increments/s
Drain burst with a change observer	44,070 increments/s	396,286 increments/s	111,971 increments/s
Lookup and send to one child	50,703 increments/s	394,177 increments/s	107,518 increments/s
Start and stop a machine	11,001 machines/s	184,502 machines/s	73,443 machines/s
Start and stop a parent with one child	3,823 families/s	66,899 families/s	26,940 families/s

Memory profile	Effect Machine	XState 5	XState 6 alpha	Effect runtime primitives
Idle machine	18.0 KiB	3.8 KiB	6.1 KiB	—
Raw managed process	13.3 KiB	—	—	—
Two independent idle machines	35.3 KiB	7.3 KiB	11.8 KiB	—
Idle parent with one child	63.7 KiB	5.5 KiB	8.8 KiB	—
Parent with observed child registry	72.5 KiB	—	—	—
Suspended Effect fiber	—	—	—	0.7 KiB
Effect queue with waiting fiber	—	—	—	2.8 KiB
Effect mailbox actor shell	—	—	—	3.2 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	110,589 transitions/s	1.3% MAD	106,359 transitions/s	0.6% MAD	-3.8%
Drain burst with terminal fence	56,364 increments/s	1.7% MAD	56,176 increments/s	0.8% MAD	-0.3%
Drain burst with a change observer	44,288 increments/s	0.3% MAD	44,070 increments/s	0.6% MAD	-0.5%
Lookup and send to one child	50,299 increments/s	2.0% MAD	50,703 increments/s	0.4% MAD	+0.8%
Start and stop a machine	10,195 machines/s	1.3% MAD	11,001 machines/s	2.2% MAD	+7.9%
Start and stop a parent with one child	3,604 families/s	0.7% MAD	3,823 families/s	0.6% MAD	+6.1%
Idle machine heap per unit	23.4 KiB	0.0% MAD	18.0 KiB	0.0% MAD	-23.0%
Raw managed process heap per unit	18.4 KiB	0.0% MAD	13.3 KiB	0.0% MAD	-27.8%
Two independent idle machines heap per unit	46.0 KiB	0.0% MAD	35.3 KiB	0.0% MAD	-23.3%
Idle parent with one child heap per unit	73.7 KiB	0.0% MAD	63.7 KiB	0.0% MAD	-13.6%
Parent with observed child registry heap per unit	82.6 KiB	0.0% MAD	72.5 KiB	0.0% MAD	-12.2%

Versions and interpretation

• Effect Machine: 0.3.0
• XState 5: 5.32.5
• XState 6 alpha: 6.0.0-alpha.27
• Effect runtime primitives: 4.0.0-beta.105

Higher throughput is better; lower heap is better. Variability is the median absolute deviation across independent processes, relative to their median. Runtime measurements on shared GitHub-hosted hardware remain informational, so small differences should be confirmed across multiple workflow runs.