Wait for child process to die in case of critical errors

Ported the regression test from OHAI-455 to mixlib-shellout, which
revealed a race condition in the way shellout reaps the child after a
failed exec (most commonly caused by attempting to run a command that
doesn't exist). The call to waitpid2 used WNOHANG to avoid hanging
indefinitely if an error was caused but the child process was still
alive, but this results in the child process not getting reaped if it
exits after the call to waitpid2. In a single run of the stress test,
this occurred 94/100 times, so it is very likely that mixlib-shellout
will leak zombies for the ENOENT case without this change.

1 files changed, 32 insertions, 0 deletions

diff --git a/spec/mixlib/shellout_spec.rb b/spec/mixlib/shellout_spec.rb
index 89f21e7..23d9a13 100644
--- a/spec/mixlib/shellout_spec.rb
+++ b/spec/mixlib/shellout_spec.rb
@@ -777,6 +777,38 @@ describe Mixlib::ShellOut do
         end
       end
 
+      context "when running a command that doesn't exist" do
+
+        let(:cmd) { "/bin/this-is-not-a-real-command" }
+
+        def shell_out_cmd
+          Mixlib::ShellOut.new(cmd)
+        end
+
+        it "reaps zombie processes after exec fails [OHAI-455]" do
+          # NOTE: depending on ulimit settings, GC, etc., before the OHAI-455 patch,
+          # ohai could also exhaust the available file descriptors when creating this
+          # many zombie processes. A regression _could_ cause Errno::EMFILE but this
+          # probably won't be consistent on different environments.
+          created_procs = 0
+          100.times do
+            begin
+              shell_out_cmd.run_command
+            rescue Errno::ENOENT
+              created_procs += 1
+            end
+          end
+          created_procs.should == 100
+          reaped_procs = 0
+          begin
+            loop { Process.wait(-1); reaped_procs += 1 }
+          rescue Errno::ECHILD
+          end
+          reaped_procs.should == 0
+        end
+      end
+
+
       context 'with open files for parent process' do
         before do
           @test_file = Tempfile.new('fd_test')