[alexander-akait]

Stacked on #389: this branch contains its commit. Please merge #389 first; this diff then shrinks to its own commit (7f62c3d).

Summary

Each compiler of a MultiCompiler kept its own worker and its own program for its TypeScript check. Runs that overlap in time were already shared (sharedRuns in check.js). Compilers that build one after another, though (parallelism: 1, or dependencies between configs), each built and held the whole program.

• Shared workers:
  • Workers are kept in a module-level map keyed by sharingKey("typescript", options), the same key concurrent runs are shared by. It is now exported from check.js.
  • Each worker counts the compilers using it, and ends once the last one lets go: on shutdown or watchClose, or in cleanup() for a one-shot build.
  • Options that cannot be written down fall back to today's per-compiler key.
• Per-run cancellation (on top of perf: stop a TypeScript run nothing will report once the next rebuild starts #389): with a shared worker, "stop every run issued so far" could stop another compiler's live run.
  • createSolo now writes a run's number into one of 64 slots of the shared Int32Array.
  • cancel(answer) stops exactly the run that promise belongs to.
• The in-process path (threads: false) still keeps a program per compiler, so it is garbage-collected with the compiler.

Measurements

Setup: 600 .ts files, a two-compiler MultiCompiler with the same TypeScript check, a watch with the first build plus one rebuild after an edit.

	wall	CPU	peak RSS
main, parallelism: 1	10.24 / 9.68 / 10.27 s	18.7–20.0 s	803–853 MB
this PR, parallelism: 1	5.68 / 5.80 / 5.59 s	9.8–10.4 s	467–483 MB
main, parallel	5.25 s	9.9 s	481 MB
this PR, parallel	5.45 s	9.9 s	468 MB

One compiler alone takes 5.5 s, 10 CPU-s and about 450 MB, so two sequential compilers now cost about what one does.

One-shot sequential builds are unchanged by this PR. A one-shot compiler ends its worker when its build is done, or the thread would keep the process alive. #383's persisted builder state is what makes the second compiler cheap there.

Tests

• test/typescript/share.test.js:
  • A TypeScript mock records whether each builder program was built fresh or from the previous one.
  • Two compilers with parallelism: 1 in watch mode must record ["fresh", "reused"].
  • With the key forced back to per compiler, the test fails (fresh, fresh).
• test/typescript/cancel.test.js from perf: stop a TypeScript run nothing will report once the next rebuild starts #389 still passes with per-run cancellation.
• Lint, tsc, schema lint, prettier, cspell and the full suite (332 tests) pass locally.

---

Generated by Claude Code

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📥 Commits

Reviewing files that changed from the base of the PR and between 0abded0 and bfa4584.

📒 Files selected for processing: 21

• .changeset/ts-share-program-across-compilers.md
• .changeset/ts-stop-stale-runs.md
• README.md
• src/check.js
• src/checks/index.js
• src/checks/typescript-program.js
• src/checks/typescript-worker.js
• src/checks/typescript.js
• src/threads.js
• test/store.test.js
• test/typescript/cancel.test.js
• test/typescript/fixtures/cancel/index.js
• test/typescript/mock/typescript-counter/index.js
• test/typescript/mock/typescript-stall/index.js
• test/typescript/share.test.js
• types/check.d.ts
• types/checks/index.d.ts
• types/checks/typescript-program.d.ts
• types/checks/typescript-worker.d.ts
• types/checks/typescript.d.ts
• types/threads.d.ts

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[linux-foundation-easycla]

• ✅ Unknown (6d8905b, 7f62c3d, 84b755e, bfa4584)
• ❌ - login: @claude / name: Claude. The commit (6d8905b, 7f62c3d, 84b755e, bfa4584) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please visit our EasyCLA portal and chat with our support bot.

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[alexander-akait]

EasyCLA fails because the commits carry a Co-Authored-By: Claude trailer that maps to no GitHub account. It is not a code failure. Whether to drop the trailer or accept the check is for the maintainers to decide, so I haven't rewritten history.

This PR now also carries #389's review fix (84b755e: never stop a run another compiler joined), merged in from that branch.

---

Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.65%. Comparing base (0abded0) to head (bfa4584).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff            @@
##             main     #390    +/-   ##
========================================
  Coverage   99.64%   99.65%            
========================================
  Files          19       19            
  Lines        5618     5750   +132     
========================================
+ Hits         5598     5730   +132     
  Misses         20       20            

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