From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58347) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dl96e-0003Tx-0Z for qemu-devel@nongnu.org; Fri, 25 Aug 2017 03:32:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dl96Z-000246-RB for qemu-devel@nongnu.org; Fri, 25 Aug 2017 03:32:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:35366) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dl96Z-00023R-If for qemu-devel@nongnu.org; Fri, 25 Aug 2017 03:32:35 -0400 Date: Fri, 25 Aug 2017 15:32:29 +0800 From: Fam Zheng Message-ID: <20170825073229.GC11465@lemon.lan> References: <20170824072202.26818-1-stefanha@redhat.com> <20170824083843.GB1866@lemon> <20170824180402.GA4368@stefanha-x1.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170824180402.GA4368@stefanha-x1.localdomain> Subject: Re: [Qemu-devel] [PATCH 0/3] iotests: clean up resources using context managers List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Kevin Wolf , qemu-devel@nongnu.org, Stefan Hajnoczi On Thu, 08/24 19:04, Stefan Hajnoczi wrote: > On Thu, Aug 24, 2017 at 04:38:43PM +0800, Fam Zheng wrote: > > On Thu, 08/24 08:21, Stefan Hajnoczi wrote: > > > Tests should declare resources upfront in a with statement. Resources are > > > automatically cleaned up whether the test passes or fails: > > > > > > with FilePath('test.img') as img_path, > > > VM() as vm: > > > ...test... > > > # img_path is deleted and vm is shut down automatically > > > > Looks good but still requires test writers to learn and remember to use FilePath > > and with. > > You cannot forget to use FilePath() unless you love typing at > os.path.join(iotests.test_dir, 'test.img'). It's much better than open > coding filename generation! > > > These are still boilerplates. Here goes my personal oppinion, so may > > not be plausible: > > > > - For VM() maybe add an atexit in the launch() method also makes sure the VM is > > eventually terminated. > > > > This means vm.shutdown() is still needed in tearDown() if there are multiple > > test methods and each of them expects a clean state, but that is probably > > still less typing (and also indenting) than the with approach, and also easy > > to remember (otherwise a test will fail). > > I looked into atexit before going this route. atexit does not have an > unregister() API in Python 2. This makes it ugly to use because some > tests do not want the resource to remain for the duration of the > process. > > A related point is that the Python objects used by atexit handlers live > until the end of the process. They cannot be garbage collected because > the atexit handler still has a reference to them. I think this shortcoming can be solved with a clean up list ("all problems in computer science can be solved by another level of indirection"): _clean_up_list = set() def _clean_up_handler(): for i in _clean_up_list: try: i() except: pass atexit.register(_clean_up_handler) class VM(...): def launch(): ... _clean_up_list.add(self.launch) def shutdown(): _clean_up_list.remove(self.launch) ... > > The with statement's identation is annoying for straightforward scripts. > More complex tests use functions anyway, so the indentation doesn't > matter there - it can be hidden by a parent function or even a > decorator. > > > - For scratch how about adding atexit in iotests.main to clean up everything in > > the scratch directory? The rationale is similar to above. > > If we decide to clear out TEST_DIR then it should be done in ./check, > not by iotests.py, so that all tests get the same file cleanup behavior, > regardless of the language they are written in. > > Also, we can then chdir(iotests.test_dir) so filename generation isn't > necessary at all. Tests can simply use 'test.img'. I guess there may > be some cases where absolute paths are necessary, but for the most part > this would be a win. Good point, ./check can even invoke scripts with scratch as their working directory. Fam > > Kevin may have an opinion on whether TEST_DIR should be cleared out or > not. > > Stefan >