fix: prevent PTY file descriptor leak in ShellExecutionService by stevenelliottjr · Pull Request #20916 · google-gemini/gemini-cli

stevenelliottjr · 2026-03-03T02:46:13Z

Summary

PTY master file descriptors were not being properly closed after process exit or manual kill, leading to system-wide PTY exhaustion on long-running sessions (macOS kern.tty.ptmx_max = 511).

Root causes identified and fixed:

destroy() never called on PTY process — The onExit handler deleted the map entry and attempted optional-chained destroy?.(), but this was fragile and insufficient. Replaced with a dedicated destroyPtyProcess() helper that safely calls destroy() with fallback to kill().
headlessTerminal.dispose() never called — The @xterm/headless Terminal with up to 300,000-line scrollback buffer was never disposed, leaking significant memory per execution. Added dispose() call in finalize() after output extraction.
kill() method only deleted map entry — When a user manually kills a process, the PTY's master FD was never closed. Now uses cleanupPtyEntry() to properly destroy the PTY and dispose the terminal.
Error path leaked FDs — If ptyInfo.module.spawn() succeeded but a later step (e.g. Terminal construction) threw, the spawned PTY was unreachable. Hoisted ptyProcess declaration outside the try block and added cleanup in the catch block.
Duplicate activePtys.delete() call — Removed the redundant first delete in onExit (the second one in finalize() is the correct location, after output is extracted).

Changes:

Add destroyPtyProcess() — safely destroys a PTY to release its master FD
Add cleanupPtyEntry() — destroys PTY + disposes terminal + removes map entry
Destroy PTY immediately in onExit before waiting for output processing
Dispose headless terminal in finalize() after extracting output
Clean up PTY in catch block for spawn-succeeded-but-init-threw path
Use cleanupPtyEntry() in kill() instead of bare map delete

Test plan

All 55 existing tests pass (no regressions)
New test: kill() calls destroy() on PTY process and clears activePtys
New test: normal exit cleans up all resources (PTY destroyed, all maps cleared)
Manual verification: run 500+ commands in a session and verify /dev/ptmx FD count stays stable
Verify lsof -c node | grep ptmx | wc -l doesn't grow unbounded

…e-gemini#15945) PTY master file descriptors were not being properly closed after process exit or manual kill, leading to system-wide PTY exhaustion on long-running sessions (macOS kern.tty.ptmx_max = 511). Changes: - Add destroyPtyProcess() helper that safely calls destroy() with fallback to kill() for closing PTY master FDs - Add cleanupPtyEntry() helper that destroys PTY, disposes the headless terminal scrollback buffers, and removes the activePtys map entry - Call destroyPtyProcess() immediately in onExit handler to release FDs before waiting for output processing - Dispose headless terminal in finalize() after extracting output, freeing up to 300k-line scrollback buffer memory - Clean up PTY in catch block when spawn succeeds but later initialization (e.g. Terminal construction) throws - Use cleanupPtyEntry() in kill() to properly destroy PTY instead of only deleting the map entry - Hoist ptyProcess declaration outside try block so catch block can access it for cleanup - Remove duplicate activePtys.delete() call in onExit handler Tests: - Add test verifying kill() calls destroy() on PTY process - Add test verifying all resources are cleaned up after normal exit

gemini-code-assist · 2026-03-03T02:46:33Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request delivers crucial fixes for resource leaks within the shell execution service, specifically targeting PTY (Pseudo-Terminal) processes and their associated headless terminals. By introducing dedicated cleanup functions and refining the lifecycle management of PTYs, it prevents the accumulation of open file descriptors and memory, thereby resolving issues like system-wide PTY exhaustion and memory leaks in long-running sessions.

Highlights

PTY File Descriptor Leak Prevention: Introduced destroyPtyProcess to safely close PTY master file descriptors, addressing system-wide PTY exhaustion.
Comprehensive Resource Cleanup: Implemented cleanupPtyEntry to centralize and ensure proper destruction of PTY processes and disposal of headless terminals.
Memory Leak Fix for Headless Terminals: Ensured headless terminals are explicitly disposed in finalize() after output extraction to prevent significant memory leaks.
Error Path Leak Mitigation: Addressed PTY file descriptor leaks that occurred when PTY spawn succeeded but subsequent initialization steps failed.
Refined PTY Lifecycle Management: Corrected PTY cleanup logic in onExit and kill methods, removing redundant deletions and ensuring timely resource release.

Changelog

packages/core/src/services/shellExecutionService.test.ts
- Added a new test to verify that the kill() method correctly calls destroy() on the PTY process and clears activePtys.
- Added a new test to confirm that all associated resources are properly cleaned up after a normal PTY exit.
packages/core/src/services/shellExecutionService.ts
- Introduced a new private static method destroyPtyProcess to safely destroy a PTY process and release its file descriptors, with a fallback to kill() if destroy() is unavailable.
- Implemented a new private static method cleanupPtyEntry to encapsulate the complete cleanup process for a PTY entry, including destroying the PTY, disposing the headless terminal, and removing it from activePtys.
- Modified the executeWithPty method to declare ptyProcess outside the try block, allowing for its cleanup in the catch block if an error occurs after spawning but before full initialization.
- Updated the onExit handler to immediately call destroyPtyProcess to release the PTY's master file descriptor as soon as the process exits.
- Ensured that headlessTerminal.dispose() is called within the finalize() function after extracting the output, preventing memory leaks from the scrollback buffer.
- Added a call to destroyPtyProcess in the catch block of executeWithPty to clean up PTY file descriptors if an error occurs during the setup phase after a successful spawn.
- Replaced the direct this.activePtys.delete(pid) call in the kill method with this.cleanupPtyEntry(pid) to ensure comprehensive resource cleanup.
- Removed a redundant this.activePtys.delete(ptyProcess.pid) call from the onExit handler, as the cleanup is now handled in finalize() or by cleanupPtyEntry().

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Code Review

This pull request effectively addresses several file descriptor and memory leaks in the ShellExecutionService by introducing robust cleanup mechanisms for PTY processes. The changes are well-structured, with new helper functions for destroying PTYs and cleaning up associated resources. The fixes cover normal exit, manual kill, and error paths during initialization. The added tests correctly verify the new cleanup logic. I've found one critical issue where a resource leak could still occur, and I've provided a suggestion to fix it.

cocosheng-g · 2026-04-09T21:26:05Z

Hi @stevenelliottjr, this PR is being closed due to merge conflicts and 29 days of inactivity. To keep the review queue manageable, we are closing stale blocked PRs. Please feel free to re-open this PR or open a new one once the issues are resolved! Thank you for your contribution.

stevenelliottjr requested a review from a team as a code owner March 3, 2026 02:46

gemini-code-assist Bot reviewed Mar 3, 2026

View reviewed changes

gemini-cli Bot added priority/p1 Important and should be addressed in the near term. area/core Issues related to User Interface, OS Support, Core Functionality help wanted We will accept PRs from all issues marked as "help wanted". Thanks for your support! labels Mar 3, 2026

This was referenced Mar 3, 2026

Bug: PTY Shell aborts orphan nested background processes causing OS-level resource exhaustion #20941

Closed

fix(core): secure pty process tree teardown to prevent zombie orphaning #20945

Closed

cocosheng-g closed this Apr 9, 2026

cocosheng-g mentioned this pull request Apr 9, 2026

System-wide PTY exhaustion due to file descriptor leak #15945

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fix: prevent PTY file descriptor leak in ShellExecutionService#20916

fix: prevent PTY file descriptor leak in ShellExecutionService#20916
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stevenelliottjr:fix/pty-fd-leak-15945

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stevenelliottjr commented Mar 3, 2026

Summary

Root causes identified and fixed:

Changes:

Test plan

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gemini-code-assist Bot commented Mar 3, 2026

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