@Martin
We could list all the hypothetical breaking cases but I don't think that's
useful. Every case is different and we should address issues that belong to
the real use case. So, until it becomes an issue it's only speculation and
leads to over-engineering and it's a waste of time and effort. He could be
fine with deleting the cache entry. If it's not fine, he'll then seek for
another solution.
2013/8/17 Martin Cooper <mfncoo...@gmail.com>
> Your implementation is still subject to both potential issues I mentioned.
>
> Let's suppose M is the module you are removing from the cache in (b), and
> let's suppose the code for M includes the following lines:
>
> var b = require("./b.js");
> var thing = { ... };
>
> exports.getThing = function () { return thing; };
>
> Now, when you remove M from the cache, and load M1 in its place, "./b.js"
> is still cached, and M1 will get that instead of any new version you may
> have provided, and the mainline code of b.js will not be re-run.
>
> Also, anyone who called M.getThing() and held a reference to it will have
> a different 'thing' than anyone who later calls M1.getThing(). (I believe
> this will also prevent M from being collected, since it's still in use.)
>
> Whether these issues are okay in the context of your framework, only you
> can say. I guess as long as you, and everyone else who writes a module to
> your interface, understands all of this, you may be okay, but I do think
> it's fragile.
>
> --
> Martin Cooper
>
>
> On Sat, Aug 17, 2013 at 9:35 AM, Tony Huang <cnwz...@gmail.com> wrote:
>
>> @Martin
>>
>> I have noticed this risk. So:
>>
>> 1) This will be just a limited feature used in my framework, it might go
>> open source, but I will never try to make this a part of node.js API. So
>> the risk will affect very little area.
>>
>> 2) I will implement it in this way:
>> a) Get the old exports object from the cache
>> b) Remove the old module from the cache
>> c) Use require() to load the new module to the cache
>> d) Use new module's code_changed function to convert module state
>> e) Delete all fields of the old exports object
>> f) Copy all fields of the new exports to the old exports object
>> g) Update the status field of old exports object to the status object
>> created at step d
>> h) Update the new modules exports field to the reference to the old
>> exports object, to make sure the exports object of the module is unique in
>> the system
>>
>> Thank you for your reply and expecting more comments & advices.
>>
>>
>> On Sat, Aug 17, 2013 at 11:55 PM, Martin Cooper <mfncoo...@gmail.com>wrote:
>>
>>> There are a couple of issues with that.
>>>
>>> First, if 'mod' loaded other modules to do its job, those other modules
>>> are not removed from the cache. For example, suppose package 'foo' has main
>>> module a.js, and that loads module b.js to do some of its work. Now if you
>>> delete 'foo', or even a.js, from the cache, b.js is still cached, so when a
>>> new version of a.js is loaded, it will still use that old b.js. Hence for
>>> this to work reliably, you need to know all of the implementation files
>>> that will need to be removed from the cache, not just your entry point.
>>> That's pretty fragile.
>>>
>>> Also, depending on the nature of the modules being removed, and their
>>> usage patterns, you may end up with retained references to the now-removed
>>> (but possibly still extant) module, or objects created by it, that may
>>> result in weird behaviour later. In the OP's case, with a framework
>>> designed for this, that may not be so much of an issue, but it's still a
>>> risk, especially if the modules being removed from the cache are
>>> non-trivial and / or not written by the framework designer.
>>>
>>> --
>>> Martin Cooper
>>>
>>>
>>> On Sat, Aug 17, 2013 at 2:42 AM, George Stagas <gsta...@gmail.com>wrote:
>>>
>>>> function removeCached(mod) {
>>>> delete require.cache[require.resolve(mod)];
>>>> }
>>>>
>>>> // then
>>>>
>>>> require('foo');
>>>>
>>>> // ... later
>>>>
>>>> removeCached('foo');
>>>>
>>>>
>>>>
>>>> 2013/8/17 Tony Huang <cnwz...@gmail.com>
>>>>
>>>>> Hi all,
>>>>>
>>>>> I'm creating a framework for my game server, and developing the module
>>>>> hot update feature.
>>>>>
>>>>> My design is very similar to the Erlang hot update feature. Modules
>>>>> will be hot updated should meet the interface:
>>>>> module.exports = {
>>>>> 'status': "data",
>>>>> 'version': "1.0",
>>>>> 'init': function() {
>>>>> return initialStatus;
>>>>> },
>>>>> 'code_changed': function(oldVersion, newVersion, oldStatus) {
>>>>> return newStatus;
>>>>> }
>>>>> };
>>>>>
>>>>> So, when the module source file changes, the framework will get the
>>>>> status of original version of module, and remove it from the module cache,
>>>>> and import the new module, and invoke the code_changed method of the new
>>>>> version of module to generate the new status and assign it to the new
>>>>> module to finish the update process.
>>>>>
>>>>> As a result, I need an API to remove the module from the module cache,
>>>>> will it be possible or will this API be added in the future version of
>>>>> node?
>>>>>
>>>>> Best regards.
>>>>>
>>>>> --
>>>>> ------------------------------------------------------
>>>>> Tony Huang cnwz...@gmail.com
>>>>> wz...@hotmail.com
>>>>> wz...@vip.sina.com
>>>>>
>>>>> --
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>>
>>
>> --
>> ------------------------------------------------------
>> Tony Huang cnwz...@gmail.com
>> wz...@hotmail.com
>> wz...@vip.sina.com
>>
>> --
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