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  • WebLogic stuck thread protection

    - by doublep
    By default WebLogic kills stuck threads after 15 min (600 s), this is controlled by StuckThreadMaxTime parameter. However, I cannot find more details on how exactly "stuckness" is defined. Specifically: What is the point at which 15 min countdown begins. Request processing start? Last wait()-like method? Something else? Does this apply only to request-processing threads or to all threads? I.e. can a request-processing thread "escape" this protection by spawning a worker thread for a long task? Especially, can it delegate response writing to such a worker without 15 min countdown? My usecase is download of huge files through a permission system. Since a user needs to be authenticated and have permissions to view a file, I cannot (or at least don't know how) leave this to a simple HTTP server, e.g. Apache. And because files can be huge, download could (at least in theory) take more than 15 minutes.

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  • Is it possible to add -pedantic to GCC command line, yet have it not warn about 'long long'

    - by doublep
    I'm using mostly GCC to develop my library, but I'd like to ensure cross-compiler compatibility and especially standard conformance as much as possible. For this, I have add several -W... flags to command line. I'd also add -pedantic, but I have a problem with its warning about long long type. The latter is important for my library and is properly guarded with #if code, i.e. is not compiled on compilers that don't know it anyway. In short: can I have GCC in -pedantic mode warn about any extension except long long?

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  • Making JSP page not set the response content-type

    - by doublep
    Is it possible to make JSP pages not set any content type on response? In my setup, JSP doesn't directly generate the response, but rather an intermediate presentation, which is then processed by additional Java code that creates HTML or JSON based on that. So, can I somehow make JSP not set content-type on the response and leave it to the intermediate code? If I just remove contentType="..." in a JSP, it still defaults to text/html.

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  • Development deployment: how to achive edit-and-reload with JSP pages?

    - by doublep
    Out project uses WebLogic as web-server and uses mostly JSP for user interface. With standard setup it is possible to copy edited JSP files into the exploded deployment directory and WebLogic will automatically pick them up, recompile and serve new content through HTTP. However, is it possible to avoid copying at all, so that I just save a file in my editor and it is immediately (well, after a couple of seconds for recompilation) visible? The project uses Apache Ant as building tool. I would imagine what I want would be possible with symlinks (since this is for deployment only I don't care about cross-platformity), but then I don't see how it is possible to symlink lots of files at once with Ant. So, how do I achieve save-JSP-hit-F5-in-browser functionality either with some setting in WebLogic; or with symlinking JSPs using Apache Ant (instead of copying them as is done now); or something else completely?

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  • Is it possible to make WebLogic check REDEPLOY file more often?

    - by doublep
    [sorry for apparent shouting in the title, it's just that the file is named in all uppercase] Given advice in http://stackoverflow.com/questions/2695124 I successfully implemented and have been using autodeployment in WebLogic. This works great, but a tad too slow to my tastes, it seems like about 10 seconds pass between touching REDEPLOY file and WebLogic's start of redeployment. Is there any way I can instruct WebLogic to test timestamp on that file more often?

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  • Move constructor and assignment operator: why no default for derived classes?

    - by doublep
    Why there is default move constructor or assignment operator not created for derived classes? To demonstrate what I mean; having this setup code: #include <utility> struct A { A () { } A (A&&) { throw 0; } A& operator= (A&&) { throw 0; } }; struct B : A { }; either of the following lines throws: A x (std::move (A ()); A x; x = A (); but neither of the following does: B x (std::move (B ()); B x; x = B (); In case it matters, I tested with GCC 4.4.

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  • How to force Weblogic to start deployments in active state (i.e. not just prepared)

    - by doublep
    When I start a Weblogic instance with a deployed application, the deployment is sometimes left in prepared state, not in active state. I have to go to Weblogic Console and start the deployment manually, which is quite slow and annoying repetetive work. Since this is done on a development machine — sometimes 50 times a day, — there are no security implication as the server is only visible on the local network. Is there some way to have it always start the deployment active? Note that I'm not redeploying the application, I instead have it "constantly deployed" and stop/start the Weblogic instance using the scripts in bin directory.

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  • Updating rows using "in" operator in "where" clause

    - by doublep
    Hi. I stumbled upon SQL behavior I don't understand. I needed to update several rows in a table at once; started with just finding them: SELECT * FROM some_table WHERE field1 IN (SELECT ...) This returned a selection of about 60 rows. Now I was pretty confident I got the subquery right, so I modified the first part only: UPDATE some_table SET field2 = some_value WHERE field1 IN (SELECT ...) In other words, this was exactly as the first query after the WHERE. However, it resulted in 0 rows updated, whereas I would expect those 60. Note that the statement above would change field2, i.e. I verified that some_value was not present in the selected rows. The subquery was a modestly complicated SQL piece with 2 (different) tables, 1 view, joins and its own WHERE clause. In case this matters, it happened with Oracle Database 10g. So, the question is, why UPDATE didn't touch the rows returned by SELECT?

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  • final transient fields and serialization

    - by doublep
    Is it possible to have final transient fields that are set to any non-default value after serialization in Java? My usecase is a cache variable — that's why it is transient. I also have a habit of making Map fields that won't be changed (i.e. contents of the map is changed, but object itself remains the same) final. However, these attributes seem to be contradictory — while compiler allows such a combination, I cannot have the field set to anything but null after unserialization. I tried the following, without success: simple field initialization (shown in the example): this is what I normally do, but the initialization doesn't seem to happen after unserialization; initialization in constructor (I believe this is semantically the same as above though); assigning the field in readObject() — cannot be done since the field is final. In the example cache is public only for testing. import java.io.*; import java.util.*; public class test { public static void main (String[] args) throws Exception { X x = new X (); System.out.println (x + " " + x.cache); ByteArrayOutputStream buffer = new ByteArrayOutputStream (); new ObjectOutputStream (buffer).writeObject (x); x = (X) new ObjectInputStream (new ByteArrayInputStream (buffer.toByteArray ())).readObject (); System.out.println (x + " " + x.cache); } public static class X implements Serializable { public final transient Map <Object, Object> cache = new HashMap <Object, Object> (); } } Output: [email protected] {} [email protected] null

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  • Moving inserted container element if possible

    - by doublep
    I'm trying to achieve the following optimization in my container library: when inserting an lvalue-referenced element, copy it to internal storage; but when inserting rvalue-referenced element, move it if supported. The optimization is supposed to be useful e.g. if contained element type is something like std::vector, where moving if possible would give substantial speedup. However, so far I was unable to devise any working scheme for this. My container is quite complicated, so I can't just duplicate insert() code several times: it is large. I want to keep all "real" code in some inner helper, say do_insert() (may be templated) and various insert()-like functions would just call that with different arguments. My best bet code for this (a prototype, of course, without doing anything real): #include <iostream> #include <utility> struct element { element () { }; element (element&&) { std::cerr << "moving\n"; } }; struct container { void insert (const element& value) { do_insert (value); } void insert (element&& value) { do_insert (std::move (value)); } private: template <typename Arg> void do_insert (Arg arg) { element x (arg); } }; int main () { { // Shouldn't move. container c; element x; c.insert (x); } { // Should move. container c; c.insert (element ()); } } However, this doesn't work at least with GCC 4.4 and 4.5: it never prints "moving" on stderr. Or is what I want impossible to achieve and that's why emplace()-like functions exist in the first place?

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  • Detect template presence at compilation time

    - by doublep
    GCC up to 4.5 doesn't have standard C++0x type trait template has_nothrow_move_constructor. I could use it in my package for optimization, but I don't want to rule out one of the common compilers and don't want to overload configuration with symbols like HAVE_STD_HAS_NOTHROW_MOVE_CONSTRUCTOR. Is it somehow possible to use that template if present and just fall back to copying if not present without using any predefined configuration symbols? I also don't want to depend on Boost, since my library is small and doesn't need Boost for any other reasons. In pseudocode, I need something like: template <typename type> struct has_nothrow_move_constructor_robust : public integral_constant <bool, /* if possible */ has_nothrow_move_constructor <type>::value /* otherwise */ false> { }; Since move constructors are only for C++0x anyway, I don't mind using other C++0x features for the above definition, if at all possible.

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  • Strict pointer aliasing: is access through a 'volatile' pointer/reference a solution?

    - by doublep
    On the heels of a specific problem, a self-answer and comments to it, I'd like to understand if it is a proper solution, workaround/hack or just plain wrong. Specifically, I rewrote code: T x = ...; if (*reinterpret_cast <int*> (&x) == 0) ... As: T x = ...; if (*reinterpret_cast <volatile int*> (&x) == 0) ... with a volatile qualifier to the pointer. Let's just assume that treating T as int in my situation makes sense. Does this accessing through a volatile reference solve pointer aliasing problem? For a reference, from specification: [ Note: volatile is a hint to the implementation to avoid aggressive optimization involving the object because the value of the object might be changed by means undetectable by an implementation. See 1.9 for detailed semantics. In general, the semantics of volatile are intended to be the same in C++ as they are in C. — end note ] EDIT: The above code did solve my problem at least on GCC 4.5.

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  • Splitting a set of object into several subsets of 'similar' objects

    - by doublep
    Suppose I have a set of objects, S. There is an algorithm f that, given a set S builds certain data structure D on it: f(S) = D. If S is large and/or contains vastly different objects, D becomes large, to the point of being unusable (i.e. not fitting in allotted memory). To overcome this, I split S into several non-intersecting subsets: S = S1 + S2 + ... + Sn and build Di for each subset. Using n structures is less efficient than using one, but at least this way I can fit into memory constraints. Since size of f(S) grows faster than S itself, combined size of Di is much less than size of D. However, it is still desirable to reduce n, i.e. the number of subsets; or reduce the combined size of Di. For this, I need to split S in such a way that each Si contains "similar" objects, because then f will produce a smaller output structure if input objects are "similar enough" to each other. The problems is that while "similarity" of objects in S and size of f(S) do correlate, there is no way to compute the latter other than just evaluating f(S), and f is not quite fast. Algorithm I have currently is to iteratively add each next object from S into one of Si, so that this results in the least possible (at this stage) increase in combined Di size: for x in S: i = such i that size(f(Si + {x})) - size(f(Si)) is min Si = Si + {x} This gives practically useful results, but certainly pretty far from optimum (i.e. the minimal possible combined size). Also, this is slow. To speed up somewhat, I compute size(f(Si + {x})) - size(f(Si)) only for those i where x is "similar enough" to objects already in Si. Is there any standard approach to such kinds of problems? I know of branch and bounds algorithm family, but it cannot be applied here because it would be prohibitively slow. My guess is that it is simply not possible to compute optimal distribution of S into Si in reasonable time. But is there some common iteratively improving algorithm?

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  • How to interrupt a waiting C++0x thread?

    - by doublep
    I'm considering to use C++0x threads in my application instead of Boost threads. However, I'm not sure how to reimplement what I have with standard C++0x threads since they don't seem to have an interrupt() method. My current setup is: a master thread that manages work; several worker threads that carry out master's commands. Workers call wait() on at least two different condition variables. Master has a "timed out" state: in this case it tells all workers to stop and give whatever result they got by then. With Boost threads master just uses interrupt_all() on a thread group, which causes workers to stop waiting. In case they are not waiting at the moment, master also sets a bool flag which workers check periodically. However, in C++0x std::thread I don't see any replacement for interrupt(). Do I miss something? If not, how can I implement the above scheme so that workers cannot just sleep forever?

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  • Can 'iterator' type just subclass 'const_iterator'?

    - by doublep
    After another question about iterators I'm having some doubts about custom containers. In my container, iterator is a subclass of const_iterator, so that I get conversion from non-const to const "for free". But is this allowed or are there any drawbacks or non-working scenarios for such a setup?

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  • Strict pointer aliasing: any solution for a specific problem?

    - by doublep
    I have a problem caused by breaking strict pointer aliasing rule. I have a type T that comes from a template and some integral type Int of the same size (as with sizeof). My code essentially does the following: T x = some_other_t; if (*reinterpret_cast <Int*> (&x) == 0) ... Because T is some arbitary (other than the size restriction) type that could have a constructor, I cannot make a union of T and Int. (This is allowed only in C++0x only and isn't even supported by GCC yet). Is there any way I could rewrite the above pseudocode to preserve functionality and avoid breaking strict aliasing rule? Note that this is a template, I cannot control T or value of some_other_t; the assignment and subsequent comparison do happen inside the templated code. (For the record, the above code started breaking on GCC 4.5 if T contains any bit fields.)

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