Powershell: Background process hangs until UI is triggered

[xdhmoore]

I'm seeing some weird behavior trying to pipe a command to AutoHotkey. It seems to hang in the background until a pwsh UI event causes it to complete.

Steps to reproduce

'WinMaximize, ahk_class ENMainFrame' | D:\path\to\AutoHotkey\AutoHotkey.exe *

Expected behavior

Completes within a few seconds and maximizes the target window. It leaves no AutoHotkey processes running:

PS D:\projects> ps auto*
PS D:\projects>

Actual behavior

The command returns quickly, but the target window is not maximized, and there remains a background process:

PS D:\projects> ps auto*

 NPM(K)    PM(M)      WS(M)     CPU(s)      Id  SI ProcessName
 ------    -----      -----     ------      --  -- -----------
     12     1.96       7.65       0.03   13804   1 AutoHotkey

This background process hangs without maximizing the window for 7+ minutes if the terminal is left alone. However, if I hold down the ENTER key, (displaying a series of new prompts), within a few seconds the targeted window will be maximized and the background process will terminate. Similarly, I can type .\ and then hold TAB for a few seconds (cycling through file name completions) with the same effect. Also, adding a & at the end fixes the problem:

'WinMaximize, ahk_class ENMainFrame' | D:\tools\AutoHotkey\AutoHotkey.exe * & 

Environment data

This behavior is present with:

• pwsh (7.0.3) with ConEmu
• pwsh (7.0.3) with traditional windows terminal ui
• pwsh -NoProfile (7.0.3)

But not present with:

• powershell (5.1.18362.752, after adjusting the default encoding)
• cmd

$PSVersionTable :

Name                           Value
----                           -----
PSVersion                      7.0.3
PSEdition                      Core
GitCommitId                    7.0.3
OS                             Microsoft Windows 10.0.18363
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[SeeminglyScience]

So AutoHotkey isn't a console application, so typically PowerShell doesn't wait for it's completion before returning. I think stdin is still being shared though, so AutoHotkey thinks it's still waiting for more script.

As a workaround, if you pipe the output of AutoHotkey to something it'll force it to wait until completion and properly close stdin. e.g.

'WinMaximize, ahk_class ENMainFrame' | D:\path\to\AutoHotkey\AutoHotkey.exe * | Write-Output

[xdhmoore]

@SeeminglyScience Thanks, that workaround does work on my machine. I'm unsure of the next step. Do you think this is a AutoHotkey bug instead (maybe it's not acknowledging the EOF or something)? Should I submit a bug report to AHK? Or do you think pwsh is failing to close stdin properly in this case?

[SeeminglyScience]

It's probably mostly PowerShell's fault. The only question is if it's typically by design and AHK is just an edge case. Either way I don't think there's anything on AHK's end to do.

[msftbot[bot]]

This issue has been marked as answered and has not had any activity for 1 day. It has been closed for housekeeping purposes.