Pike-devel February 2012

pike-devel@lists.lysator.liu.se

2 participants
4 discussions

Sql.pgsql behavior in case of errors
by aldem-pikedev＠aldem.net 21 Aug '14

21 Aug '14

Hi everyone, I am preparing to use Postgres in my app, found the following strange behavior: ---snip--- Sql.Sql db = Sql.Sql("pgsql://localhost", "test", "test", "test"); db->query("BEGIN"); db->query("INSERT INTO requests (SvTrId) VALUES ('lala')"); catch(db->query("INSERT INTO requests (SvTrId) VALUES ('lala')")); db->query("INSERT INTO requests (SvTrId) VALUES ('juju')"); db->query("ROLLBACK"); ---snip--- Database is opened, row with 'lala' is inserted, second query (obviously) fails as SvTrId is the primary key, but row with 'juju' is inserted *and* appears in the database - i.e. the transaction is *committed*! Studying source code show, that once error is encounter, session is reset, i.e. running transaction is rolled back, everything is closed, temporary tables are deleted and session variables are reset as well, and after that, the next statement(s) will be committed immediately, as there is no active transaction. In my opinion, this is not exactly correct behavior when statement fails, as session still may be needed (especially temporary tables, open cursors etc). Im some cases, this is perfectly normal when SQL statement fails, especially in SERIALIZED transaction isolation level, and it would be more practical to leave the decision as of what to do to the application. Yes, this is true that it is impossible to continue executing statements in failed transaction, but temporary tables etc. may still be needed. Also, silent reconnection is not a good idea too - when there are many transactional statements are executed - it would be nice to have an option to modify this behavior. Best regards, /Alexander

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compilation handler for multi-tenant applications: update
by Bill Welliver 02 Apr '12

02 Apr '12

Hi all, A few months ago, started a conversation about what I'll call multi-tenant applications: that is, a single pike process running multiple applications (perhaps including copies of a given application) with isolated program and module spaces. The idea is to provide a similar capability to that provided by Java's ClassLoader API. That is, I'd like to be able to do the following: pike +-----------------|-----------------+ | | thread a1...an thread b1 ... bn compilation handler a compilation handler b loads classes for app1 instance 1 loads classes for app1 instance from location a,b from location a,c (perhaps) uses module foo.bar uses module foo.bar foo.bar != foo.bar though it would perhaps be acceptable if object_program(foo.bar) == object_program(foo.bar) applications would not be aware of each other (a condition of the multi-tenant contract) and thus object identity would not need to be maintained. I've been dabbling with the approach suggested at the Pike conference, which was to use a compilation handler to provide this functionality. I've come tantalizingly close, being able to use an overriden master to provide versions of compile_string() and friends that automatically select the desired compilation handler based on various criteria (such as threads in an application). While a bit clunky, it seems to allow me to control visibility of identifiers in a given application or thread, but there does seem to be a limitation that for me is fatal: the programs and module objects are cached by the master, and therefore any two applications are not truely isolated: they share a common set of modules (and join/dirnodes) and (though less problematic) precompiled programs.Because programs and modules seem to be indexed by filename, I've played around with adding a unique identifier in order to split the cache on a per-handler basis, but this hasn't worked either (programs seem to be loaded as desired, but modules are still problematic.) I've attempted to add storage of these caches in the compilation handler, but it results in extremely odd failures (for example, a given class will be cached as a zero value in the programs mapping, which means the program won't be found, even if it's on disk. As a brute force attempt to prove that the idea can work, I'm thinking about short circuiting the auto-reload functionality so that it always reloads a given class from disk. I'm not sure that this will actually prove beneficial, as modules would still be persistent. As always, any thoughts or suggestions would be welcome. Bill

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Design advice sought: Backend implementation
by Bill Welliver 01 Apr '12

01 Apr '12

I'd like to solicit some design feedback for a new feature that I'd like to contribute. I apologize for the length of this message, but hopefully it contains all of the details needed to get the conversation started. First, some quick background: Over the past few years I've written a few modules[1] that provide access to a number of technologies that are either part of Darwin or one of Apple's Darwin-based OSes (OSX, iOS, etc). A common feature that keeps occurring is their reliance on an active run loop. Normally, this is either NSRunloop or CFRunLoop (they are distinct APIs, but they share a common set of event sources.) In the past, I've resorted to adding a persistent call-out to the default back end, which is similar to the approach taken by the GTK2 module. This is normally good enough for sitatuions where events are relatively infrequent, such as GUI-input work. However, it's not always suitable for higher interrupt volumes and it also has the side effect of presenting a continual, though low, load on the CPU. This isn't a huge problem, but it's unclean and if one were to increase the frequency of the poll-out to the CF/NS run loop, the load becomes higher, and thus harder to ignore. A Solution: After doing some research on better ways to approach the problem, I discovered that CF/NS run loops use kqueue at their core. As a result, a kqueue can be added to the run loop and polled for events. That's convenient, because pike uses kqueue on Darwin in its default backend, Pike.PollDeviceBackend. Swapping out the direct call to kevent() with one that calls the run loop results in "native" Pike I/O working the way it should, plus Darwin layered functionality working properly as well (and low CPU utilization, too). I think that this is a useful new feature to add to Pike, but I've got some concerns about how best to include it. Right now, I've created a branch called hww3/cfrunloop_backend[2] that includes the functionality and swaps out the existing implementation under Darwin. That is, of course, the simplest approach, but I think is probably not the best idea: Pros: - Uses kqueue() at its core, so the existing backend will fire events in the same way. - Allows a number of technologies to function normally when used from with Pike processes, without the use of hacks. Cons: - There is exactly one Run Loop per thread, which, if used universally, could present issues because this means behavior would differ from other Backends. - There is slightly more overhead per trip through the backend due to events being single-shot. This means that the kqueue has to be re-added to the runloop each loop. I don't think it's a major overhead, it still exists. Alternate Implementations: A second approach would be to provide an additional backend implementation, say Pike.CFBackend, that's available on Darwin based systems. I see one or two problems with this, though: - There would need to be a way to activiate this selectively at runtime, something like set_default_backend(Pike.CFBackend()), which probably doesn't exist right now, right? - Because 90% of the implementation would be shared with PollDeviceBackend, I think it would involve a fair amount of code duplication inside of backend.cmod, which I think would make maintenance more difficult. A third (and right now, I believe the best) approach would be to add one or two methods to Pike.Backend that could be implemented by PollDeviceBackend on Darwin and be used to activate this alternate mode. For example: int(0..1) has_client_mode() which would return true if there were a client optimization (I suggest client because CFRunLoop would be more useful for client apps than traditional server based apps, though that's certainly not an either/or situaiton) and: void enable_client_mode(int(0..1)) that would trigger calls to CFRunLoopRunInMode() instead of kevent() directly. Input Sought: I think either of the two alternative approaches would be just fine, assuming that the concerns could be addressed. I'm just not sure which would be best from a design and implementation standpoint (I sort of think the last option would be simplest for _me_ to get working, but if someone has desire to help tackle it, I'd be game to play along). The upshot of allowing the proposed backend changes for other folks using Pike are that: a) SDL and GL becomes usable out of the box on OSX b) I am prepared to contribute a few pieces of code, namely: - FSEvents module - Updated Filesystem.Monitor that uses FSEvents on Darwin and inotify on Linux to eliminate polling - DNS_SD querying support on OSX - ObjectiveC bridge (possibly) Hopefully we can have a bit of discussion about the options and approaches and come up with a solution that works without being terribly inconvenient. Please do drop me a note if anything about this proposal is unclear. Best, Bill [1] Public.ObjectiveC, Public.System.FSEvents, Public.IO.IOWarror, additions to DNS-SD; SDL and GL on OSX also share this requirement. [2] http://hg.welliver.org/pike/changesets, not yet pushed to the pike master repo.

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paging Peter Bortas
by H. William Welliver III 16 Feb '12

16 Feb '12

I don't have Peter's email address, so hopefully he's monitoring this… I'd like to get working on a 7.8 release but don't really have any idea what's involved, aside from change log entries (which I'm working on, slowly). Anything you might have for me to go on in that department (even if it's a rough outline) would be greatly appreciated! Bill

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Pike-devel February 2012