System.Net.AutoWebProxyScriptWrapper.CloseAppDomain C# (CSharp) Method

        private static void CloseAppDomain(int index)
        {
            AppDomain appDomain;

            // Locking s_AppDomains must happen in a CER so we don't orphan a lock that gets taken by AppDomain.DomainUnload.
            bool lockHeld = false;
            RuntimeHelpers.PrepareConstrainedRegions();
            try
            {
                try { }
                finally
                {
                    Monitor.Enter(s_AppDomains.SyncRoot);
                    lockHeld = true;
                }

                if (s_CleanedUp)
                {
                    return;
                }
                appDomain = (AppDomain) s_AppDomains[index];
            }
            finally
            {
                if (lockHeld)
                {
                    Monitor.Exit(s_AppDomains.SyncRoot);
                    lockHeld = false;
                }
            }

            try
            {
                // Cannot call Unload() in a lock shared by OnDomainUnload() - deadlock with ADUnload thread.
                // So we may try to unload the same domain twice.
                AppDomain.Unload(appDomain);
            }
            catch (AppDomainUnloadedException) { }
            finally
            {
                RuntimeHelpers.PrepareConstrainedRegions();
                try
                {
                    try { }
                    finally
                    {
                        Monitor.Enter(s_AppDomains.SyncRoot);
                        lockHeld = true;
                    }

                    s_AppDomains.Remove(index);
                }
                finally
                {
                    if (lockHeld)
                    {
                        Monitor.Exit(s_AppDomains.SyncRoot);
                    }
                }
            }
        }