Minor improvement to TritonService

[kpedro88]

PR description:

While testing an algorithm with a significantly longer inference time than the one used for the SonicTriton unit test, I re-encountered the issue with the fallback server shutting down too early.

Adding some debugging info to auto_stop, I found that using $PPID for the fallback server did not actually get the PID of the cmsRun process, but rather the sh process spawned by the popen call. Apparently, this sh process hangs around long enough for the unit test to complete, if auto_stop is delayed by a few seconds (in the case of Singularity reading from cvmfs, which is slightly slower than a local read). However, this is not reliable or general.

Instead, I now pass the cmsRun PID directly when starting the fallback server. This works to avoid the previous failure (tested by setting PMAX=1 in cmsTriton). I've retained the value PMAX=5 in this PR just in case some other instability might arise.

PR validation:

Reran stress tests from #32576.

@makortel @silviodonato @qliphy it would be nice to get this into pre3 if the deadline has not passed (it's really just a minor bug fix).

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-32861/21088

• This PR adds an extra 20KB to repository

[cmsbuild]

A new Pull Request was created by @kpedro88 (Kevin Pedro) for master.

It involves the following packages:

HeterogeneousCore/SonicTriton

@makortel, @cmsbuild, @fwyzard can you please review it and eventually sign? Thanks.
@makortel, @riga, @rovere this is something you requested to watch as well.
@silviodonato, @dpiparo, @qliphy you are the release manager for this.

cms-bot commands are listed here

[kpedro88]

please test

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-32861/21089

• This PR adds an extra 20KB to repository

[cmsbuild]

Pull request #32861 was updated. @makortel, @cmsbuild, @fwyzard can you please check and sign again.

[kpedro88]

please test

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-b7e177/12815/summary.html
COMMIT: 7d47581
CMSSW: CMSSW_11_3_X_2021-02-09-2300/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week1/cms-sw/cmssw/32861/12815/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 37
• DQMHistoTests: Total histograms compared: 2751765
• DQMHistoTests: Total failures: 1
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2751742
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 36 files compared)
• Checked 156 log files, 37 edm output root files, 37 DQM output files

[makortel]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @silviodonato, @dpiparo, @qliphy (and backports should be raised in the release meeting by the corresponding L2)

[qliphy]

+1