> On May 8, 2020, at 2:17 PM, Leif Hedstrom <[email protected]> wrote: > > > >> On May 8, 2020, at 12:29 PM, Alan Carroll <[email protected] >> <mailto:[email protected]>> wrote: >> >> Consider a situation with option (1) with two remap rules: >> >> map http://example.one <http://example.one/> http://example.one >> <http://example.one/> @plugin=txn_box.so @reloadable=false blah blah blah >> map http://example.two <http://example.two/> http://example.two >> <http://example.two/> @plugin=txn_box.so @reloadable=true blah blah >> >> Does that DSO get reloaded on a reload of "remap.config"? > > > It should get reloaded for the second, not for the first. As far as I > understand, this is fine, the Gancho made the code such that as long as > something uses some version of a plugin, it will be kept forever.
Now, if this gets too complicated (but I don’t see why, the old remap is still available when the new one is being created), I’d say produce an Error(). — Leif > > — Leif > > > >> >> >> On Fri, May 8, 2020 at 9:58 AM Sudheer Vinukonda <[email protected] >> <mailto:[email protected]>> wrote: >> Ah, true. I get the misunderstanding now. Yeah, I don’t mean to have >> reloadable flexibility per remap line either, but just per “(remap)plugin”. >> >> And the only point I was trying to make was to let that the flexibility be >> determined by the user and not implicitly by the fact that a plugin was used >> in mixed mode. And yeah sorry, I totally missed the problem with making it a >> remap level param instead of a plugin level param. So, I still prefer your >> approach 1, except it’d be clearer if it’s named something more obvious >> indicating non-reload ability than “@global” (but, naming is hard and I >> can’t think of a short/succinct better name :() >> >> >> >>> On May 8, 2020, at 7:33 AM, Alan Carroll <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> >>> Sudheer, I understand the point you are making, I just consider it >>> irrelevant. Let me give Leif an example to illustrate why - TxnBox. It >>> shares data between the global and remap configurations at run time via >>> static variables. If you enable remap DSO reloading for TxnBox, it will >>> crash on the first transaction that hits a remap rule. It doesn't matter if >>> it's actually been reloaded or not. However your organization does plugin >>> updates, TxnBox will still crash in that situation. Even in your example, >>> Sudheer, there's no _choice_ about whether a particular plugin can be DSO >>> reloaded, it's a result of the implementation. As you yourself write, you >>> can't enable it for those plugins without changing the code. No >>> configuration cleverness will get around that. >>> >>> For plugins that do support DSO reloading, the enablement is still per >>> plugin, not per remap rule. Moreover, if we went with option (3) it would >>> be simple to have to plugin support a configuration / load time option to >>> enable or disable DSO reloading. In general, if the plugin can be DSO >>> reloaded, it's unclear why it shouldn't be except in unusual circumstances >>> which are depending on the plugin implementation. >>> >>> For Sudheer, I remain unclear on what exact flexibility you want, given the >>> constraints created by a specific plugin's implementation. I've re-read >>> your note and AFAICT it assumes doing DSO reload or not *per plugin*, which >>> is also my point. I dislike (1) because it makes no sense to me to have >>> this change between remap rules for a specific plugin. I think it's better >>> to have the plugin decide if that's possible and, if needed, provide >>> configuration to disable it if needed. Speaking specifically for TxnBox, I >>> must forbid you from enabling DSO reloading. Even in your case, it might be >>> reasonable to have this for plugins that you have not yet updated (which is >>> actually the case with TxnBox - I'm limited by a requirement for ATS 7 >>> compatibility, so I can't change that feature at the current time). >>> >>> On Thu, May 7, 2020 at 10:11 PM Leif Hedstrom <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> >>>> On May 7, 2020, at 8:12 PM, Alan Carroll <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> >>>> Leif; >>>> >>>> If the plugin can be global or remap but not both, I don't see why (2) >>>> limits anything. The entire issue is irrelevant for such plugins, because >>>> the situation of reloading the remap DSO but not the global cannot occur, >>>> In fact, option (3) or (4) would enable detecting this and issuing a >>>> warning. >>> >>> Ah yes, good point. However, still the same problem, one can very much want >>> to use say header_rewrite as both global and remap plugin at the same time, >>> and be fine with the fact that it doesn’t reload as a “global”, but you >>> want it to reload as a remap. We use that plugin in this way for example. >>> >>> I still feel that option 2) is a bad option, but I’m ok with the others >>> (still with a preference towards #1). I think a finer granular control >>> mechanism here is a good idea. >>> >>> I’d also be curious to hear which of the core plugins are having problems >>> here, in most cases, there’s a no dependency between the global >>> instantiation, and the per remap instantiation. Sudheer and LinkedIn have >>> many internal plugins that do experience this problem however, so I’m >>> guessing that maybe you have similar custom internal plugins? >>> >>> Cheers, >>> >>> — Leif >>> >>>> >>>> Approach (1) was my first thought, but I think the problem there is >>>> whether the plugin can work as a global and a reloadable remap is a >>>> property of the plugin implementation, not any particular remap rule. That >>>> is, for a specific plugin, there's really no choice about whether to use >>>> "@plugin" or "@global" - the configuration must get it right or the plugin >>>> crashes. Every time. Every rule. It is for this reason I disagree with >>>> Leif's view the user should decide. The user's opinion is irrelevant - the >>>> plugin works in this mode, or it doesn't. And as our friends at LinkedIn >>>> discovered, some rather basic C++ decisions (such as using static >>>> variables) will prevent a plugin from working in this mode. On the other >>>> hand, if the plugin uses the "User Args" feature then it can work, in >>>> which case what's the point of disabling the DSO reload? Unless the plugin >>>> implementor is concerned about code skew between the global and remap >>>> versions, which again the user is not qualified to decide. >>>> >>>> My personal preference is (3), but I suspect after mysterious crashes with >>>> plugins, we will have been happier with (4). >>>> >>>> On Thu, May 7, 2020 at 7:42 PM Sudheer Vinukonda >>>> <[email protected] <mailto:[email protected]>> wrote: >>>> +1 on the general idea to make the reloadability customizable per plugin. >>>> >>>> However, I think it'd be more simple, cleaner and intuitive to not tie it >>>> to whether or not a plugin is used both as a global and remap plugin. >>>> >>>> In other words, approach (1) below but, instead of calling it "@global", >>>> we could add a param which says "@reloadable=false" (the default value for >>>> "@reloadable" can be "true"). >>>> >>>> The same param can then be used, when we eventually add relodability to >>>> global plugins as well. >>>> >>>> Thoughts? >>>> >>>> >>>> >>>> >>>> On Thursday, May 7, 2020, 05:24:09 PM PDT, Alan Carroll >>>> <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> >>>> >>>> As part of the ATS 9 upgrade, a feature was added so that remap plugins >>>> could have their DSO reloaded. This means not just the configuration, but >>>> the implementation itself. While very useful, this has some unfortunate >>>> side effects with plugins that are used in both a global and remap >>>> context. To alleviate this, a configuration variable as added to disable >>>> the feature. >>>> >>>> Although reasonable, this is a rather heavy handed way to deal with the >>>> problem. What would be better is the ability to reload the DSO or not on a >>>> per remap plugin basis. I have a few ways this could be done: >>>> >>>> 1) Add the keyword "@global" to "remap.config". This would behave exactly >>>> as "@plugin" except it would prohibit reloading of the DSO for that plugin. >>>> >>>> 2) Have the remap reload configuration check to see if the plugin is also >>>> a global plugin and disable remap DSO reload for that plugin. >>>> >>>> 3) Add a flag to the global plugin registry information which can be set >>>> during TSPluginInit which disables DSO reloading for that plugin, should >>>> it occur in "remap.config". This is similar to (2) but requires a plugin >>>> to prohibit DSO reloading. The call woud be TSPluginDSOReloadEnable(flag) >>>> and would only be valid when called from TSPluginInit. >>>> >>>> 4) As (3), except the flag is set by default and must be cleared to enable >>>> DSO reloading in "remap.config". >>>> >>>> I'm willing to see if I can make this work, but I would like to have some >>>> feedback on the preferred approach first.
