Make native select differential deterministic

[loreste]

Summary

• ensure only channel b can be ready for the first select
• delay channel a so it deterministically feeds the second select
• remove scheduler-order flakiness from the C/native differential gate

Validation

• ./scripts/native-compiler-test.sh
• prior merged CI run: ASan, UBSan, TSan, GCC, LLVM, cross-compile, product claims, benchmark gates, and macOS/Linux platform jobs passed

Summary by CodeRabbit

• Documentation
  • Updated the select-syntax example timing to make channel readiness and timeout behavior clearer.
  • Increased selection timeout values for more reliable example execution.

[coderabbitai]

📝 Walkthrough

Walkthrough

The select syntax example updates sender delays and increases both timeout values so the first selection targets channel b readiness.

Changes

Select syntax example

Layer / File(s)	Summary
Channel timing and timeout adjustments examples/select_syntax.mko	Sender kickoff delays are revised so channel b is ready for the first selection, and both select timeouts change from 500 to 2000.
Estimated code review effort: 1 (Trivial)	~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly matches the main change: making the native select differential test deterministic.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch agent/memory-safety-runtime-install

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@examples/select_syntax.mko`:
- Around line 13-17: Update the setup around chan_selectn in the first select
test so b’s sender is confirmed to have started or become ready before kicking
the delayed sender for a. Replace the fixed-delay-only ordering with an explicit
synchronization mechanism, while preserving the existing intent that only b is
selectable initially and retaining the current select timeout and values.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: a2ffe787-54e6-4a30-8414-2b2fd8cb648d

📥 Commits

Reviewing files that changed from the base of the PR and between cf5e37e and 3e20dda.

📒 Files selected for processing (1)

• examples/select_syntax.mko

[coderabbitai]

🩺 Stability & Availability | 🟠 Major | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Verify the ordering guarantees of crew kickoff and channel readiness.
rg -n -C5 '\bt\.kick\s*\(|fn\s+kick\b|sleep_ms\b|chan_select' .

Repository: loreste/mako

Length of output: 50369

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🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== candidate crew definitions =="
rg -n -C8 '\bkick\b|struct .*Crew|type .*Crew|impl .*Crew|fn new_crew|Crew::|t\.kick' src runtime examples/testing examples/select_syntax.mko --glob '!runtime/native_bridge.c' | head -n 240

echo
echo "== select_syntax.mko and chan_select implementation references =="
cat -n examples/select_syntax.mko
rg -n -C7 'select|chan_select' runtime src --glob '!runtime/native_bridge.c' | head -n 220

Repository: loreste/mako

Length of output: 29009

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== focused crew/channel/select runtime symbols =="
rg -n -C6 'struct mako_crew|type mako_crew|crew_\w*|Crew|kick\(|chan_new|chan_send|chan_select|mako_chan_select|mako_native_chan_select|selectn|selectn' runtime src -g '*.c' -g '*.h' -g '*.rs' | head -n 300

echo
echo "== relevant exact files if any =="
git ls-files | rg '(^|/)(?i)(crew|select|channel|thread|task).*\.(c|h)$|(^|/)(mako_rt|mako_vm|mako_sched).*\.(c|h)$|src/.*select.*|src/.*crew.*'

Repository: loreste/mako

Length of output: 16622

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== runtime/mako_rt.h relevant ranges =="
sed -n '5030,5115p' runtime/mako_rt.h
sed -n '5115,5150p' runtime/mako_rt.h
sed -n '5440,5515p' runtime/mako_rt.h
sed -n '5590,5660p' runtime/mako_rt.h

echo
echo "== crew kickoff and scheduling references =="
rg -n -C8 'kick|Crew|crib|Task|task|spawn|thread|pthread|schedule|runnable|ready|selectn\(|chan_selectn\(' runtime/mako_rt.h runtime -g '*.c' -g '*.h' --glob 'runtime/mako_rt.h'

Repository: loreste/mako

Length of output: 50369

---

🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== exact ranges requested =="
sed -n '5030,5115p' runtime/mako_rt.h
sed -n '5115,5150p' runtime/mako_rt.h

echo
echo "== select-n implementation candidates =="
rg -n -C10 'mako_chan_selectn|static inline .*select.*' runtime/mako_rt.h

echo
echo "== crew/task implementation candidates =="
rg -n -C10 'struct .*Task|struct .*Crew|typedef .*Task|typedef .*Crew|kick\(|Kick\(|pthread_create|pthread_mutex|pthread_cond|runnable|ready|spawn|join' runtime/mako_rt.h --glob 'runtime/mako_rt.h'

Repository: loreste/mako

Length of output: 50368

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🏁 Script executed:

#!/bin/bash
set -euo pipefail

echo "== crew/task implementation tail =="
wc -l runtime/mako_rt.h
sed -n '5646,5950p' runtime/mako_rt.h

echo
echo "== select syntax lowering =="
rg -n -C8 'Select|stmts|ChanSelect|select_syntax|mako_chan_select' src --glob '*.rs'

Repository: loreste/mako

Length of output: 50369

---

Wait for b’s send to start before delaying a.

chan_selectn starts scanning from the current round-robin index, so if both buffered channels become ready before the first select, either arm can be chosen. A fixed delay does not guarantee a is still unavailable, so the test remains scheduler-dependent; establish readiness ordering between kicking/beginning the delayed sender and the first select.

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@examples/select_syntax.mko` around lines 13 - 17, Update the setup around
chan_selectn in the first select test so b’s sender is confirmed to have started
or become ready before kicking the delayed sender for a. Replace the
fixed-delay-only ordering with an explicit synchronization mechanism, while
preserving the existing intent that only b is selectable initially and retaining
the current select timeout and values.