Consider a situation with option (1) with two remap rules: map http://example.one http://example.one @plugin=txn_box.so @reloadable=false blah blah blah map 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"? On Fri, May 8, 2020 at 9:58 AM Sudheer Vinukonda <[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]> > 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]> wrote: > >> >> >> On May 7, 2020, at 8:12 PM, Alan Carroll < >> [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]> 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]> 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. >>> >>> >>
