Can't Redirect Mercurial stdout/stderr Under Windows 2012 R2 Noninteractive Session

[Steve Barnes]

On 22/09/14 23:38, Mads Kiilerich wrote:
> On 09/20/2014 06:07 AM, Jensen, Aaron wrote:
>> We have several automated build jobs that check changes into 
>> Mercurial. If they encounter unmerged heads on the outgoing server, 
>> the scripts will pull down those changes, merge them, then push 
>> everything back out (repeated until the push succeeds). In some 
>> cases, Mercurial would ask for input from the user, which caused our 
>> automated jobs to timeout. We can't use the --interactive flag 
>> because there are occasions we *didn't* want to choose `y` to 
>> Mercurial's questions.
>>
>> So, we wrote a wrapper script in PowerShell which starts a Mercurial 
>> as a background process and monitors it. If the script detects 
>> Merurial is asking a question, it will abort Mercurial, and fail the 
>> build with a friendly error message. This script also redirects 
>> Mercurial's stdout/stderr streams, reads them in, writes the errors 
>> to PowerShell's error stream, and converts Mercurial's output to 
>> objects, which consumers of our script use to perform additional 
>> processing.
>>
>> Unfortunately, beginning with Windows 2012 R2 (we were using Windows 
>> 2008 R2 previously), the background Mercurial process started hanging 
>> when run by our build server (CruiseControl.NET running as an 
>> Administrator). It does not happen when I'm running at an interactive 
>> console. After several hours of research, it looks like redirecting 
>> Mercurial's stdout/stderr streams causes Mercurial to freeze and not 
>> output anything. Even running `hg help` hangs.
>>
>> Here's how you can reproduce. Under CruiseControl.NET, or some other 
>> non-interactive process/service, run the following PowerShell code 
>> [1]. I'm pretty sure this is something in Mercurial because I 
>> switched the background process to `cmd.exe` with arguments of `@( 
>> '/c', 'echo fubar' )` and that process completes successfully.
>
> It sounds like a blocking buffer. Obviously 'hg status' without output 
> passes? How about short output like 'hg id'?
>
>> Any ideas what would be causing this? How can I troubleshoot further?
>
> Unless you or some other windows expert can figure out how to debug 
> it, I would suggest replacing your complex wrapper script with a small 
> extension that just modify merges. Or perhaps even simpler: let it run 
> non-interactively and merge as it wants and then check the output 
> whether it did some of the forbidden actions.
>
> /Mads
>
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>
I would also suggest that this might be the sort of job that would be 
better written as a (wx)python script - using hglib 
<http://mercurial.selenic.com/wiki/PythonHglib> or the command server 
<http://mercurial.selenic.com/wiki/CommandServer#Example_client> in 
python you can control mercurial quite thoroughly and if you use 
wxPython you can even have a GUI to show the progress, number of errors, 
etc.

Gadget/Steve



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