microsoft/Terminal

[cont] [DefTerm] Some invocations can cause deadlocks in terminal + another GUI application in Attach mode

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#19749 opened on Jan 15, 2026

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Area-DefAppHelp WantedIssue-BugPriority-2Product-Terminal

Description

Windows Terminal version

No response

Windows build number

No response

Other Software

No response

Steps to reproduce

Same steps as https://github.com/microsoft/terminal/issues/14131 More here: https://github.com/microsoft/terminal/issues/14131#issuecomment-3731555688

Expected Behavior

no 5000ms timeout from SendMessageTimeoutW: SMTO_NOTIMEOUTIFNOTHUNG

Actual Behavior

5000ms because the window is newly hung (by call to system())

Contributor guide

Tech stack
cpp
Domain
desktop
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
mostly clear
Prerequisites
Windows API knowledgeTerminal codebaseC++ experienceDebugging skills
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20
Research direction
Investigate the deadlock described in issue #19749, which is related to #14131. Focus on the use of SendMessageTimeoutW and the call to system() that causes the window to hang. Examine the DefTerm handling code and how attach mode interacts with other GUI applications. Review the linked comment (#14131#issuecomment 3731555688) for additional context and potential reproduction steps.