fix(install): optimize isolated linker to avoid O(N²) complexity in resumeUnblockedTasks

[robobun]

Summary

• Fixes bun install hanging on Windows when using the isolated (symlink) linker with large monorepos
• Adds a blocked_entries hashmap to track which entries are currently blocked
• Reduces complexity from O(N²) to O(B * D) where B is the number of blocked entries

Problem

When using the isolated linker (linker = "symlink" or auto mode with workspaces), bun install would hang indefinitely on large monorepos (~1500+ packages) on Windows, consuming 5-6GB+ of RAM with CPU usage dropping to near zero.

The root cause was in resumeUnblockedTasks() which was called after every task completion and iterated through ALL entries (O(N)) to find blocked tasks. With ~1500 packages, this resulted in approximately N² iterations (1500 task completions × 1500 entries = 2.25 million iterations), plus additional O(D * P) work for cycle detection per blocked task.

Solution

Instead of iterating through all entries on each task completion, we now:

1. Track blocked entries in a hashmap (blocked_entries) when they become blocked
2. Only iterate through this much smaller list in resumeUnblockedTasks()
3. Remove entries from the hashmap when they are unblocked

This reduces the complexity from O(N² * D * P) to O(B * D * P) where B is the number of currently blocked entries (typically much smaller than N).

Test plan

• Build succeeds
• Existing tests pass (semver.test.ts, architecture-match.test.ts)
• Manual testing with large monorepo on Windows (I don't have access to Windows)

Closes #25970

🤖 Generated with Claude Code

[robobun]

^{Updated 3:44 AM PT - Jan 12th, 2026}

❌ Your commit 386de73b has 2 failures in Build #34548 (All Failures):

• test/integration/next-pages/test/dev-server.test.ts - 1 failing on 🍎 14 aarch64
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 2019 x64-baseline
• test/js/bun/test/parallel/test-http-should-emit-close-when-connection-is-aborted.ts - timeout on 🪟 2019 x64

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🧪   To try this PR locally:

bunx bun-pr 25983

That installs a local version of the PR into your bun-25983 executable, so you can run:

bun-25983 --bun

[coderabbitai]

Walkthrough

Optimizes task resumption logic in the Installer by introducing a blocked_entries map to track currently blocked entries. Replaces inefficient full-scan approach in resumeUnblockedTasks with targeted iteration over only blocked entries, reducing complexity in large dependency graphs.

Changes

Cohort / File(s)	Summary
Installer optimization src/install/isolated_install/Installer.zig	Adds public blocked_entries field to track blocked entries; extends deinit for cleanup; updates onTaskBlocked to record blocked entries; replaces O(N) full-scan approach in resumeUnblockedTasks with targeted iteration over blocked entries subset, collecting unblockable entries and updating their step to symlink_dependency_binaries before restarting tasks.

Suggested reviewers

• dylan-conway
• taylordotfish

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title directly describes the main change: optimizing isolated linker by avoiding O(N²) complexity in resumeUnblockedTasks, which matches the primary objective of fixing the performance hang.
Description check	✅ Passed	The PR description addresses both template sections: clearly explains what the PR does (fixes hang, adds blocked_entries hashmap) and covers verification (build succeeds, existing tests pass), though manual Windows testing is marked as TODO.
Linked Issues check	✅ Passed	The PR directly addresses issue #25970's objective of resolving the indefinite hang in bun install with the symlink linker on large monorepos by reducing algorithmic complexity from O(N²) to O(B*D).
Out of Scope Changes check	✅ Passed	All changes are scoped to addressing the identified performance issue: blocked_entries hashmap addition, deinit extension, onTaskBlocked recording, and resumeUnblockedTasks optimization—all directly serve the complexity reduction objective.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In @src/install/isolated_install/Installer.zig:
- Around line 24-26: The field blocked_entries should be made private by
renaming it to #blocked_entries; update its declaration in Installer and replace
all internal references (e.g., in onTaskBlocked, resumeUnblockedTasks, deinit)
to use this.#blocked_entries so accesses compile and follow the repository's
private-field convention.

📜 Review details

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Review profile: ASSERTIVE

Plan: Pro

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📥 Commits

Reviewing files that changed from the base of the PR and between beccd01 and 386de73.

📒 Files selected for processing (1)

• src/install/isolated_install/Installer.zig

🧰 Additional context used

📓 Path-based instructions (2)

**/*.zig

📄 CodeRabbit inference engine (CLAUDE.md)

In Zig code, be careful with allocators and use defer for cleanup

Files:

• src/install/isolated_install/Installer.zig

src/**/*.zig

📄 CodeRabbit inference engine (src/CLAUDE.md)

src/**/*.zig: Use the # prefix for private fields in Zig structs, e.g., struct { #foo: u32 };
Use Decl literals in Zig, e.g., const decl: Decl = .{ .binding = 0, .value = 0 };
Place @import statements at the bottom of the file in Zig (auto formatter will handle positioning)
Never use @import() inline inside functions in Zig; always place imports at the bottom of the file or containing struct

Files:

• src/install/isolated_install/Installer.zig

🧠 Learnings (1)

📚 Learning: 2026-01-05T16:32:07.551Z

Learnt from: alii
Repo: oven-sh/bun PR: 25474
File: src/bun.js/event_loop/Sigusr1Handler.zig:0-0
Timestamp: 2026-01-05T16:32:07.551Z
Learning: In Zig codebases (e.g., Bun), treat std.posix.sigaction as returning void and do not perform runtime error handling for its failure. The Zig standard library views sigaction failures as programmer errors (unreachable) because they only occur with invalid signals like SIGKILL/SIGSTOP. Apply this pattern across Zig files that call sigaction (e.g., crash_handler.zig, main.zig, filter_run.zig, process.zig) and ensure failures are not handled as recoverable errors; prefer reaching an explicit unreachable/compile-time assumption when such failures are detected.

Applied to files:

• src/install/isolated_install/Installer.zig

🔇 Additional comments (3)

src/install/isolated_install/Installer.zig (3)

28-31: LGTM!

The blocked_entries hashmap is properly deallocated using the same allocator (this.lockfile.allocator) that is used for insertions in onTaskBlocked. Memory management is correct.

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223-224: LGTM!

The blocked entry is correctly tracked after setting the step to .blocked. The put operation handles the case if the entry was somehow already present. OOM handling is consistent with the codebase patterns.

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326-343: LGTM! Clean optimization with correct two-phase approach.

The implementation correctly:

1. Collects unblocked entries first to avoid mutating blocked_entries during iteration
2. Uses swapRemove for O(1) removal from the hashmap
3. Properly deallocates the temporary to_unblock list via defer

This effectively reduces complexity from O(N) to O(B) per task completion, addressing the performance issue in large monorepos.

[coderabbitai]

🧹 Nitpick | 🔵 Trivial

Consider marking blocked_entries as private with # prefix.

The field is only accessed within internal Installer methods (onTaskBlocked, resumeUnblockedTasks, deinit). As per coding guidelines for this repository, private fields should use the # prefix.

♻️ Suggested change

     /// Tracks which entries are currently blocked, avoiding O(N) iteration over all entries
     /// in resumeUnblockedTasks. Only modified from the main thread.
-    blocked_entries: std.AutoArrayHashMapUnmanaged(Store.Entry.Id, void) = .empty,
+    #blocked_entries: std.AutoArrayHashMapUnmanaged(Store.Entry.Id, void) = .empty,

Note: This would require updating all references to use this.#blocked_entries.

🤖 Prompt for AI Agents

In @src/install/isolated_install/Installer.zig around lines 24 - 26, The field
blocked_entries should be made private by renaming it to #blocked_entries;
update its declaration in Installer and replace all internal references (e.g.,
in onTaskBlocked, resumeUnblockedTasks, deinit) to use this.#blocked_entries so
accesses compile and follow the repository's private-field convention.

[github-actions]

Closing this PR because it has been inactive for more than 90 days.