Share zero-input process logic

[SandroMaglione]

Summary

• Share the immutable execution descriptor used by zero-input starts of the same machine definition.
• Keep input-bearing and resumed starts instance-specific, while retaining invoked-child sessions in their existing runtime-address-keyed WeakMap.
• Add regression coverage proving concurrent invoked children and distinct input-bearing starts remain isolated.

This removes one duplicated closure bundle and invoke-session map per ordinary actor without changing the public API, transition semantics, or type inference. Three independent local heap-slope runs measured approximately 7% less retained heap for idle and independent actors and 6% less for parent-with-child actors; lifecycle throughput remained effectively neutral.

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 (unchanged; local budget still passes)
• Reviewed the automated runtime-performance report, when runtime behavior changed

[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)	0.23s	0.22s
machine.handle (depth 8)	0.52s	0.51s
machine.handle (depth 12)	0.56s	0.56s
machine.handle (depth 16)	0.60s	0.60s
machine.handle (depth 24)	0.69s	0.69s
machine.handle (wide depth 16)	0.77s	0.76s
machine.handle (parallel/history/choice)	0.62s	0.63s
machine.handle (4 successive calls)	0.58s	0.59s
machine exact input/output/error/services	0.51s	0.52s
execution adapter readiness	0.59s	0.58s

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	99,530 transitions/s	134,894 transitions/s	122,945 transitions/s
Drain burst with terminal fence	82,397 increments/s	398,762 increments/s	112,874 increments/s
Drain burst with a change observer	60,483 increments/s	396,179 increments/s	112,626 increments/s
Lookup and send to one child	77,186 increments/s	395,707 increments/s	108,083 increments/s
Start and stop a machine	18,797 machines/s	184,468 machines/s	73,774 machines/s
Start and stop a parent with one child	7,512 families/s	68,507 families/s	26,795 families/s

Effect runtime reference points

Scenario	Effect Machine	Effect runtime primitives
Start and stop a raw compiled process	30,628 processes/s	—
Start and interrupt a suspended fiber	—	161,238 fibers/s
Start and stop a queue worker	—	112,032 workers/s
Start and stop an actor shell	—	102,796 actors/s
Start and stop two actor shells	—	63,780 families/s
Update an owner-only mutable snapshot	—	317,863,954 updates/s
Update a synchronized snapshot	—	1,504,929 updates/s
Create, resolve, and await a terminal latch	—	1,409,692 latches/s

Memory profile	Effect Machine	XState 5	XState 6 alpha	Effect runtime primitives
Idle machine	7.0 KiB	3.8 KiB	6.1 KiB	—
Raw generic managed process	12.3 KiB	—	—	—
Raw compiled process	7.6 KiB	—	—	—
Two independent idle machines	13.5 KiB	7.3 KiB	11.8 KiB	—
Idle parent with one child	15.8 KiB	5.5 KiB	8.8 KiB	—
Parent with observed child registry	19.9 KiB	—	—	—
Parent with observed invoked child snapshots	15.9 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	110,642 transitions/s	1.2% MAD	99,530 transitions/s	0.7% MAD	-10.0%
Drain burst with terminal fence	88,826 increments/s	1.7% MAD	82,397 increments/s	1.7% MAD	-7.2%
Drain burst with a change observer	66,039 increments/s	2.4% MAD	60,483 increments/s	1.5% MAD	-8.4%
Lookup and send to one child	83,985 increments/s	0.9% MAD	77,186 increments/s	0.9% MAD	-8.1%
Start and stop a machine	18,875 machines/s	2.4% MAD	18,797 machines/s	1.1% MAD	-0.4%
Start and stop a parent with one child	7,894 families/s	0.9% MAD	7,512 families/s	1.5% MAD	-4.8%
Idle machine heap per unit	7.5 KiB	0.0% MAD	7.0 KiB	0.0% MAD	-7.1%
Raw generic managed process heap per unit	12.3 KiB	0.0% MAD	12.3 KiB	0.0% MAD	-0.0%
Raw compiled process heap per unit	7.6 KiB	0.0% MAD	7.6 KiB	0.0% MAD	+0.9%
Two independent idle machines heap per unit	14.5 KiB	0.0% MAD	13.5 KiB	0.0% MAD	-7.3%
Idle parent with one child heap per unit	16.8 KiB	0.0% MAD	15.8 KiB	0.0% MAD	-6.1%
Parent with observed child registry heap per unit	21.0 KiB	0.0% MAD	19.9 KiB	0.0% MAD	-4.9%
Parent with observed invoked child snapshots heap per unit	17.0 KiB	0.0% MAD	15.9 KiB	0.0% MAD	-6.0%

Effect runtime reference change from base

Metric	Base	Base variability	PR	PR variability	Difference
Start and stop a raw compiled process	30,487 processes/s	1.2% MAD	30,628 processes/s	0.4% MAD	+0.5%
Start and interrupt a suspended fiber	165,262 fibers/s	0.6% MAD	161,238 fibers/s	0.3% MAD	-2.4%
Start and stop a queue worker	112,905 workers/s	0.4% MAD	112,032 workers/s	0.0% MAD	-0.8%
Start and stop an actor shell	102,480 actors/s	0.7% MAD	102,796 actors/s	0.4% MAD	+0.3%
Start and stop two actor shells	57,267 families/s	2.1% MAD	63,780 families/s	2.7% MAD	+11.4%
Update an owner-only mutable snapshot	316,856,781 updates/s	0.0% MAD	317,863,954 updates/s	0.0% MAD	+0.3%
Update a synchronized snapshot	1,530,454 updates/s	0.9% MAD	1,504,929 updates/s	0.4% MAD	-1.7%
Create, resolve, and await a terminal latch	1,424,702 latches/s	0.6% MAD	1,409,692 latches/s	1.6% MAD	-1.1%

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.