Use owner-only compiled machine state

[SandroMaglione]

Summary

• store compiled process snapshots in a lightweight owner-only mutable reference
• keep terminal reservation and observer installation atomic at synchronous Effect boundaries
• revision-check effectful updates across asynchronous boundaries and stress-test first observation racing on-demand completion

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 (not applicable)
• Reviewed the automated type-performance report, when the public TypeScript API or inference changed (pnpm perf:types; public API unchanged)
• Reviewed the automated runtime-performance report, when runtime behavior changed

Local three-process comparison: burst +11.5%, observed burst +11.2%, child delivery +19.0%, idle heap -15.2%, and parent-child heap -12.8%.

[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	0.03s	0.03s
Import effect-machine	0.03s	0.03s
Machine.defineStates (3 states)	0.10s	0.10s
Machine.make (3 states, 2 events)	0.16s	0.16s
machine.handle (3 states, 2 transitions)	0.24s	0.24s
machine.handle (depth 8)	0.51s	0.51s
machine.handle (depth 12)	0.55s	0.55s
machine.handle (depth 16)	0.60s	0.59s
machine.handle (depth 24)	0.71s	0.70s
machine.handle (wide depth 16)	0.77s	0.76s
machine.handle (parallel/history/choice)	0.62s	0.60s
machine.handle (4 successive calls)	0.57s	0.59s
machine exact input/output/error/services	0.50s	0.51s
execution adapter readiness	0.57s	0.56s

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 9V74 80-Core Processor with Node v24.18.0.

Pull request baseline

Scenario	Effect Machine	XState 5	XState 6 alpha
Plan counter transitions	129,109 transitions/s	174,616 transitions/s	142,856 transitions/s
Drain burst with terminal fence	109,121 increments/s	500,315 increments/s	133,164 increments/s
Drain burst with a change observer	86,464 increments/s	494,566 increments/s	132,672 increments/s
Lookup and send to one child	104,951 increments/s	493,131 increments/s	130,090 increments/s
Start and stop a machine	30,741 machines/s	227,998 machines/s	91,017 machines/s
Start and stop a parent with one child	9,469 families/s	91,349 families/s	37,994 families/s

Effect runtime reference points

Scenario	Effect Machine	Effect runtime primitives
Start and stop a raw compiled process	39,544 processes/s	—
Start and interrupt a suspended fiber	—	198,491 fibers/s
Start and stop a queue worker	—	144,488 workers/s
Start and stop an actor shell	—	133,316 actors/s
Start and stop two actor shells	—	82,932 families/s
Update an owner-only mutable snapshot	—	401,123,145 updates/s
Update a synchronized snapshot	—	1,979,912 updates/s
Create, resolve, and await a terminal latch	—	2,174,220 latches/s

Memory profile	Effect Machine	XState 5	XState 6 alpha	Effect runtime primitives
Idle machine	8.8 KiB	3.8 KiB	6.1 KiB	—
Raw generic managed process	13.2 KiB	—	—	—
Raw compiled process	9.6 KiB	—	—	—
Two independent idle machines	17.1 KiB	7.3 KiB	11.8 KiB	—
Idle parent with one child	22.1 KiB	5.4 KiB	8.8 KiB	—
Parent with observed child registry	33.6 KiB	—	—	—
Parent with observed invoked child snapshots	22.3 KiB	—	—	—
Suspended Effect fiber	—	—	—	0.7 KiB
Effect queue with waiting fiber	—	—	—	2.8 KiB
Effect mailbox actor shell	—	—	—	3.2 KiB
Two Effect actor shells	—	—	—	6.9 KiB

Effect Machine change from base

Metric	Base	Base variability	PR	PR variability	Difference
Plan counter transitions	129,571 transitions/s	2.7% MAD	129,109 transitions/s	1.5% MAD	-0.4%
Drain burst with terminal fence	97,025 increments/s	0.8% MAD	109,121 increments/s	3.1% MAD	+12.5%
Drain burst with a change observer	82,787 increments/s	1.1% MAD	86,464 increments/s	0.8% MAD	+4.4%
Lookup and send to one child	95,224 increments/s	0.4% MAD	104,951 increments/s	0.8% MAD	+10.2%
Start and stop a machine	27,938 machines/s	0.5% MAD	30,741 machines/s	2.4% MAD	+10.0%
Start and stop a parent with one child	9,078 families/s	4.1% MAD	9,469 families/s	2.8% MAD	+4.3%
Idle machine heap per unit	10.5 KiB	0.0% MAD	8.8 KiB	0.0% MAD	-15.9%
Raw generic managed process heap per unit	13.2 KiB	0.0% MAD	13.2 KiB	0.0% MAD	-0.0%
Raw compiled process heap per unit	11.3 KiB	0.0% MAD	9.6 KiB	0.0% MAD	-14.6%
Two independent idle machines heap per unit	20.4 KiB	0.0% MAD	17.1 KiB	0.0% MAD	-16.2%
Idle parent with one child heap per unit	25.4 KiB	0.0% MAD	22.1 KiB	0.0% MAD	-12.9%
Parent with observed child registry heap per unit	36.9 KiB	0.0% MAD	33.6 KiB	0.0% MAD	-8.9%
Parent with observed invoked child snapshots heap per unit	25.6 KiB	0.0% MAD	22.3 KiB	0.0% MAD	-12.8%

Effect runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw compiled process	37,467 processes/s	0.6% MAD	39,544 processes/s	1.7% MAD	+5.5%
Start and interrupt a suspended fiber	195,771 fibers/s	0.4% MAD	198,491 fibers/s	0.8% MAD	+1.4%
Start and stop a queue worker	144,071 workers/s	0.1% MAD	144,488 workers/s	1.3% MAD	+0.3%
Start and stop an actor shell	132,591 actors/s	0.3% MAD	133,316 actors/s	1.5% MAD	+0.5%
Start and stop two actor shells	71,782 families/s	1.5% MAD	82,932 families/s	2.0% MAD	+15.5%
Update an owner-only mutable snapshot	401,123,145 updates/s	0.0% MAD	401,123,145 updates/s	0.0% MAD	0.0%
Update a synchronized snapshot	2,008,064 updates/s	0.6% MAD	1,979,912 updates/s	1.0% MAD	-1.4%
Create, resolve, and await a terminal latch	2,127,297 latches/s	1.7% MAD	2,174,220 latches/s	1.3% MAD	+2.2%

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.