Parsing XML dies (stays blocked) when doing in parallel

[krezac]

Hello all,
I've discovered this while load-testing my app on Windows 7. When there are multiple goroutines doing XML parsing, sooner or later all of them stay stucked in xml.Parse() and the CPU load drops to zero.

It's much more probable for go run than for building and running the executable. So far I wasn't able to repro it on linux.

See the attached sample code (no request, just 10 go routines running in loop).
It should timeout after 20 seconds (or 10000 iterations) but with go run it usually ends up like

Id 8, iter: 571, elapsed: 5.018003
Id 8, iter: 572, elapsed: 5.021004
Id 8, iter: 573, elapsed: 5.023504
Id 8, iter: 574, elapsed: 5.026005
Id 8, iter: 575, elapsed: 5.029006
Done -- this is outputted after 20s - timeout expired

Any idea what can be wrong?
Thanks in advance
gokogiri-load.zip

[jbowtie]

The underlying library (libxml2) does not guarantee thread safety for multiple threads sharing the same document. It can be done but requires the caller (gokogiri in this case) to handle any locking and synchronization. I'm not surprised it has issues under load.

You should be able to parse different documents in each goroutine safely, though I don't know how feasible that is for your actual application.

[krezac]

Thanks for your reply.
I was just curious whether it's common problem (we eventually handled the
issue different way).

On Sat, May 21, 2016 at 8:56 AM, John C Barstow notifications@github.com
wrote:

The underlying library (libxml2) does not guarantee thread safety for
multiple threads sharing the same document. It can be done but requires the
caller (gokogiri in this case) to handle any locking and synchronization.
I'm not surprised it has issues under load.

You should be able to parse different documents in each goroutine
safely, though I don't know how feasible that is for your actual
application.

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