Use select.poll() for exec on linux/darwin

[jsun-splunk]

What type of PR is this?

/kind bug

What this PR does / why we need it:

For an exec call, the current WSClient implementation uses select.select() to wait for file descriptor that are ready for read. The select.select() method uses the select() system call for this. As the select() system call has a limitation where by it will return the following error if the file descriptor # is greater than 1024.

Reason: filedescriptor out of range in select()

This limitation happens at scale when are running a large number of exec calls from a single client process. Once the filedescriptor number goes pass 1024 all future exec calls will experience the above error.

By switching to select.poll() instead, we can over come this limitation. The caveat here is that select.poll() is only supported on unix based OS, where as select.select() is also support on Windows. However, even if this is the case, it would be better to use the select.poll() where possible so we can overcome this limitation even if it is on unix based OS.

Which issue(s) this PR fixes:

Similar problem was previously discussed in these issues.
#53
#106

Special notes for your reviewer:

Another option here is to use select.epoll() instead of select.poll() for linux, however, I did not fully understand the difference between the two and did not felt confident enough to try epoll.

Does this PR introduce a user-facing change?

NONE

Use select.poll() for exec on linux/darwin to improve scalability of WSClient

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[roycaihw]

/assign

Thanks for sending the fix! Please let us know when it's ready for review.

[jsun-splunk]

Hi @roycaihw - thanks for looking into this. I'm just waiting on some internal process to sign off the CLA. The PR is actually ready to be reviewed.

[jsun-splunk]

I signed it

[jsun-splunk]

/check-cla

[jsun-splunk]

/check-cla

[jsun-splunk]

i signed it

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[roycaihw]

/lgtm
/approve
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[roycaihw]

The CLA check still doesn't pass. Please make sure you've signed the CLA, and the email matches the one used in the Git commits.

[jsun-splunk]

/check-cla

[jsun-splunk]

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[jsun-splunk]

hi @roycaihw,

Now this is merged, do you know how we can update the submodule in the top leve client (https://github.com/kubernetes-client/python/tree/master/kubernetes)? I can't seem to find any instructions on how to release the submodules.

Thanks!

[roycaihw]

Please follow this instruction to update the submodule and create a PR. Thanks!