Fix IO.select([io], nil, [io]) on macOS

* It was hanging due to a bug in macOS poll(2), so we have to work around it.
* Fixes #3346

Author: eregon

CHANGELOG.md

@@ -10,6 +10,7 @@ Bug fixes:
 * Fix `IO.copy_stream` with a `Tempfile` destination (#3280, @eregon).
 * Fix `Regexp.union` negotiating the wrong result encoding (#3287, @nirvdrum, @simonlevasseur).
 * Fix `Proc#parameters` and return all the numbered parameters lower than the used explicitly ones (@andrykonchin).
+* Fix `IO.select([io], nil, [io])` on macOS, it was hanging due to a bug in macOS `poll(2)` (#3346, @eregon, @andrykonchin).
 
 Compatibility:
 

src/main/ruby/truffleruby/core/io.rb

@@ -767,6 +767,21 @@ def self.select(readables = nil, writables = nil, errorables = nil, timeout = ni
         raise IOError, 'closed stream' if io.closed?
         io
       end
+
+      if Truffle::Platform.darwin? and !errorables.empty?
+        if errorables.all? { |obj| readables.include?(obj) or writables.include?(obj) }
+          # On macOS, if all errorables are in readables or writables, we make errorables empty,
+          # because if non-empty they cause a bug with macOS poll(2), detailed in
+          # https://github.com/oracle/truffleruby/issues/3346#issuecomment-1847323741
+          # Errors are still reported, POLLIN_SET and POLLOUT_SET both include POLLERR.
+          # POLLPRI is only for TCP OOB data (rare, not portable, poll(2) hangs on macOS with TCP OOB, another macOS bug),
+          # and other "high priority data" which seems to not exist or unused since there is no way to read that data.
+          errorables = []
+          errorable_ios = []
+        else
+          raise IOError, 'IO.select call on macOS with error IOs not in read IOs or write IOs, this is not supported due to poll(2) bugs on macOS'
+        end
+      end
     else
       errorables = []
       errorable_ios = []