Fix use of select() instead of poll()

[mehrdadn]

Why are these changes needed?

Negative timeout for poll() was not translated to infinite timeout for select().

Related issue number

#631

#6363 (line)

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://ray.readthedocs.io/en/latest/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failure rates at https://ray-travis-tracker.herokuapp.com/.

[AmplabJenkins]

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[pcmoritz]

Thanks for the fix! Let's also put and ifdef here and keep the poll code for linux and macOS. On linux, select only works for file descriptors <= 1024 which could cause problems, see https://linux-tips.com/t/is-it-possible-to-listen-file-descriptor-greater-than-1024-with-select/45.

[mehrdadn]

@pcmoritz Oh shoot, thanks for the heads up! I didn't realize it's a bit vector! I thought it's an array of file descriptors (that's how they're implemented in Windows) so I assumed there can't be a problem if there's only a single file descriptor.

I pushed a new patch to switch to poll on non-Windows systems now, hopefully it should take care of that.

[mehrdadn]

@pcmoritz I just pushed an identical patch for Redis's ae.c in this PR as well, hope that's fine.

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