Limit concurrent NativeAOT compiles to stop MSBuild nodes dying of memory pressure [CI]

scripts/test-linux-agent-build.py

@@ -198,6 +198,26 @@ esac
                         self.assertEqual(package.getmember('moshiro-agent').mode, 0o755)
                     subprocess.run(['sha256sum', '-c', archive.name + '.sha256'], cwd=output, check=True, capture_output=True)
 
+    def test_aot_slots_limit_concurrent_compiles_and_free_on_exit(self):
+        with tempfile.TemporaryDirectory() as temp:
+            slots = Path(temp) / 'slots'
+            env = dict(os.environ, MOSHIRO_AOT_SLOTS='1', MOSHIRO_AOT_SLOT_DIR=str(slots), MOSHIRO_AOT_SLOT_WAIT='1')
+            script = str(ROOT / 'ci/with-aot-slot.sh')
+            holder = subprocess.Popen(['bash', script, 'sleep', '5'], env=env)
+            try:
+                deadline = time.monotonic() + 5
+                while not (slots / 'slot-0').exists() and time.monotonic() < deadline:
+                    time.sleep(0.05)
+                time.sleep(0.3)
+                busy = subprocess.run(['bash', script, 'true'], env=env, capture_output=True, text=True)
+                self.assertEqual(busy.returncode, 1, busy.stderr)
+                self.assertIn('no NativeAOT slot', busy.stderr)
+            finally:
+                holder.kill()
+                holder.wait()
+            env['MOSHIRO_AOT_SLOT_WAIT'] = '5'
+            self.assertEqual(subprocess.run(['bash', script, 'sh', '-c', 'exit 7'], env=env).returncode, 7)
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)