[GR-20446] Fix Process.wait2 to return nil when WNOHANG flag is given and the process is still running

PullRequest: truffleruby/3286

Author: bjfish

CHANGELOG.md

@@ -13,6 +13,7 @@ Compatibility:
 
 * Fix `Marshal.dump` to raise an error when an object has singleton methods (@bjfish).
 * `Exception#full_message` now defaults the order to `:top` like CRuby 3+ (@eregon).
+* Fix `Process.wait2` to return `nil` when the `WNOHANG` flag is given and the child process is still running (@bjfish).
 
 Performance:
 

spec/ruby/core/process/wait2_spec.rb

@@ -33,4 +33,13 @@
     -> { Process.wait2 }.should raise_error(Errno::ECHILD)
     -> { Process.wait2 }.should raise_error(StandardError)
   end
+
+  it "returns nil if the child process is still running when given the WNOHANG flag" do
+    IO.popen(ruby_cmd('STDIN.getbyte'), "w") do |io|
+      pid, status = Process.wait2(io.pid, Process::WNOHANG)
+      pid.should be_nil
+      status.should be_nil
+      io.write('a')
+    end
+  end
 end

spec/tags/core/process/wait2_tags.txt

@@ -1 +1,2 @@
 fails:Process.wait2 returns the pid and status of child process
+slow:Process.wait2 returns nil if the child process is still running when given the WNOHANG flag

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

@@ -541,7 +541,11 @@ def self.last_status
   #
   def self.wait2(input_pid=-1, flags=nil)
     status = Truffle::ProcessOperations.wait(input_pid, flags, true, true)
-    [status.pid, status]
+    if status
+      [status.pid, status]
+    else
+      nil
+    end
   end
 
   #