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• Where is mpx386.6 and start.c in Minix 3.2?

  - by John Bowlinger

  I'm trying to follow along in Operating Systems and Implementation 3rd edition and I'm now at the part in the book where Tanenbaum is discussing bootup and kernel process switching. He keeps referring to these 2 files (mpx386.s, start.c) that are supposedly in a directory called kernel, but I can't seem to find them. In the root directory, when I go to boot/minix/3.2.0/kernel, kernel just seems to be a binary file that is illegible in terminal. There also seems to be a bunch of mod01-mod12 gz binary files as well in the 3.2.0 directory. Am I in the wrong directory, or is there something I need to install and do to read kernel? I would like to follow along with the book to what's on my screen, instead of constantly flipping back and forth. I realize alot of files are completely different from this book published in 2006 and I accept that, but this seems to be a critical juncture of the book and the operating system as a whole. If it's any consolation, I'm running the OS in Virtualbox on a 64-bit Macbook.

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• Enterprise Platform in Python, Design Advice

  - by Jason Miesionczek

  I am starting the design of a somewhat large enterprise platform in Python, and was wondering if you guys can give me some advice as to how to organize the various components and which packages would help achieve the goals of scalability, maintainability, and reliability. The system is basically a service that collects data from various outside sources, with each outside source having its own separate application. These applications would poll a central database and get any requests that have been submitted to perform on the external source. There will be a main website and REST/SOAP API that should also have access to the central data service. My initial thought was to use Django for the web site, web service and data access layer (using its built-in ORM), and then the outside source applications can use the web service(s) to get the information they need to process the request and save the results. Using this method would allow me to have multiple instances of the service applications running on the same or different machines to balance out the load. Are there more elegant means of accomplishing this? i've heard of messaging systems such as MQ, would something like that be beneficial in this scenario? My other thought was to use a completely separate data service not based on Django, and use some kind of remoting or remote objects (in they exist in Python) to interact with the data model. The downside here would be with the website which would become much slower if it had to push all of its data requests through a second layer. I would love to hear what other developers have come up with to achieve these goals in the most flexible way possible.

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• Wicket application + Apache + mod_jk - AJP queues are filling up!

  - by nojyarg

  Dear community, We are having a Wicket-based Java application deployed in a production server cluster using Apache (2.2.3) with mod_jk (1.2.30) as load balancing component w/ sticky session and Jboss 5 as application container for the Java application. We are inconsistently seeing an issue in our production environment where our AJP queues between Apache and Jboss as shown in the JMX console fill up with requests to the point where the application server is no longer taking on any new requests. When looking at all involved system components (overall traffic, load db, process list db, load of all clustered application server nodes) nothing points towards a capacity issue which would explain why the calls are being stalled in the AJP queue. Instead all systems appear sufficiently idle. So far, our only remedy to this issue is to restart the appservers and the load balancer which only occasionally clears the AJP queues. We are trying to figure out why the queues are filling up to the point that no calls get returned to the end user although the system is not under a high load. Has anyone else experienced similar problems? Are there any other system metrics we should monitor that could explain the queuing behavior? Is this potentially a mod_jk issue? If so, is it advisable to swap mod_jk with mod_cluster to resolve the issue? Any advice is highly appreciated. If I can provide additional information for the sake of troubleshooting I would be more than willing to do so. /Ben

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• Java, Massive message processing with queue manager (trading)

  - by Ronny

  Hello, I would like to design a simple application (without j2ee and jms) that can process massive amount of messages (like in trading systems) I have created a service that can receive messages and place them in a queue to so that the system won't stuck when overloaded. Then I created a service (QueueService) that wraps the queue and has a pop method that pops out a message from the queue and if there is no messages returns null, this method is marked as "synchronized" for the next step. I have created a class that knows how process the message (MessageHandler) and another class that can "listen" for messages in a new thread (MessageListener). The thread has a "while(true)" and all the time tries to pop a message. If a message was returned, the thread calls the MessageHandler class and when it's done, he will ask for another message. Now, I have configured the application to open 10 MessageListener to allow multi message processing. I have now 10 threads that all time are in a loop. Is that a good design?? Can anyone reference me to some books or sites how to handle such scenario?? Thanks, Ronny

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• How do I prevent qFatal() from aborting the application?

  - by Dave

  My Qt application uses Q_ASSERT_X, which calls qFatal(), which (by default) aborts the application. That's great for the application, but I'd like to suppress that behavior when unit testing the application. (I'm using the Google Test Framework.) I have by unit tests in a separate project, statically linking to the class I'm testing. The documentation for qFatal() reads: Calls the message handler with the fatal message msg. If no message handler has been installed, the message is printed to stderr. Under Windows, the message is sent to the debugger. If you are using the default message handler this function will abort on Unix systems to create a core dump. On Windows, for debug builds, this function will report a _CRT_ERROR enabling you to connect a debugger to the application. ... To supress the output at runtime, install your own message handler with qInstallMsgHandler(). So here's my main.cpp file: #include <gtest/gtest.h> #include <QApplication> void testMessageOutput(QtMsgType type, const char *msg) { switch (type) { case QtDebugMsg: fprintf(stderr, "Debug: %s\n", msg); break; case QtWarningMsg: fprintf(stderr, "Warning: %s\n", msg); break; case QtCriticalMsg: fprintf(stderr, "Critical: %s\n", msg); break; case QtFatalMsg: fprintf(stderr, "My Fatal: %s\n", msg); break; } } int main(int argc, char **argv) { qInstallMsgHandler(testMessageOutput); testing::InitGoogleTest(&argc, argv); return RUN_ALL_TESTS(); } But my application is still stopping at the assert. I can tell that my custom handler is being called, because the output when running my tests is: My Fatal: ASSERT failure in MyClass::doSomething: "doSomething()", file myclass.cpp, line 21 The program has unexpectedly finished. What can I do so that my tests keep running even when an assert fails?

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• How can I abstract out the core functionality of several Rails applications?

  - by hornairs

  I'd like to develop a number of non-trivial Rails applications which all implement a core set of functionality but each have certain particular customizations, extensions, and aesthetic differences. How can I pull the core functionality (models, controllers, helpers, support classes, tests) common to all these systems out in such a way that updating the core will benefit every application based upon it? I've seen Rails Engines but they seem to be too detached, almost too abstracted to be built upon. I can seem them being useful for adding one component to an existing app, for example bolting on a blog engine to your existing e-commerce site. Since engines seem to be mostly self contained, it seems difficult and inconvenient to override their functionality and views while keeping DRY. I've also considered abstracting the code into a gem, but this seems a little odd. Do I make the gem depend on the Rails gems, and the define models & controllers inside it, and then subclass them in my various applications? Or do I define many modules inside the gem that I include in the different spots inside my various applications? How do I test the gem and then test the set of customizations and overridden functionality on top of it? I'm also concerned with how I'll develop the gem and the Rails apps in tandem, can I vendor a git repository of the gem into the app and push from that so I don't have to build a new gem every iteration? Also, are there private gem hosts/can I set my own gem source up? Also, any general suggestions for this kind of undertaking? Abstraction paradigms to adhere to? Required reading? Comments from the wise who have done this before? Thanks!

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• What are the benefits and risks of moving to a Model Driven Architecture approach?

  - by Tone

  I work for a company with about 350 employees and we are in the process of growing. Our current codebase is not structured very well and we are looking both at how to improve it immediately (by organizing objects into namespaces, separating concerns, etc.) and moving to a model driven architecture approach, where we model and design everything first with uml, then generate code from that model. We have been looking heavily at Sparx Systems Enterprise Architect (EA) (which is UML 2.0 capable) and we are also considering the tools in VS 2010. I know there are other tools out there (Rational XDE being one) but I really do not think we can spend $1500+ per license at this point. I'm not looking for answers on which tool is better than another but more for experiences moving from a cowboy coding environment (that is, little planning and design, just jump in and start coding) to a model driven architecture. Looking back was it helpful to your organization? What are the pain points? What are the risks? What are the benefits?

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• C# array of objects - conditional validation

  - by fishdump

  Sorry about the vague title! I have an class with a number of member variables (system, zone, site, ...) public sealed class Cello { public String Company; public String Zone; public String System; public String Site; public String Facility; public String Process; //... } I have an array of objects of this class. private Cello[] m_cellos = null; // ... I need to know whether the array contains objects with the same site but different systems, zones or companies since such a situation would be illegal. I have various other checks to make but they are all along similar lines. The Array class has a number of functions that look promising but I am not very up on defining 'key selector' functions and things like that. Any suggestions or pointers would be greatly appreciated. --- Alistair.

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• Why trigger query fails in the sqlite with Qt?

  - by dexterous_stranger

  I am a beginner in the SQL. I am using SQLite, Qt - on embedded systems. I want to put a trigger here. The trigger is that whenever the primary key Id is greater than 32145, then channelNum=101 should be set. I want to set the attrib name - text also, but I got the compilation issue. I believe that the setting of trigger is the part of DDL - Data definition language. Please let me know that if I am wrong here. Here is my create db code. I get the sql query error. Also please do suggest how to set the text attrib = "COmedy". /** associate db with query **/ QSqlQuery query ( m_demo_db ); /** Foreign keys are disabled by default in sqlite **/ /** Here is the pragma to turn them on first **/ query.exec("PRAGMA foreign_keys = ON;"); if ( false == query.exec()) { qDebug()<<"Pragma failed"; } /** Create Table for storing user preference LCN for DTT **/ qDebug()<<"Create Table postcode.db"; query.prepare(" CREATE TABLE dttServiceList (Id INTEGER PRIMARY KEY, attrib varchar(20), channelNum integer )" ); if ( false == query.exec()) { qDebug()<<"Create dttServiceList table failed"; } /** Try placing trigger here **/ triggerQuery = "CREATE TRIGGER upd_check BEFORE INSERT ON dttServiceList \ FOR EACH ROW \ BEGIN \ IF Id > 32145 THEN SET channelNum=101; \ END IF; \ END; "; query.prepare(triggerQuery); if ( false == query.exec()) { qDebug()<<"Trigger failed !!"; qDebug() << query.lastError(); } Also, how to set the text name in the trigger - I want to SET attrib = "Comedy".

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• How can I specify processor affinity?

  - by BenAlabaster

  I have an application that's having some trouble handling multi-processor systems. It's not an app that I have a particular affection for modifying and would like to avoid it if possible. However, I'm not above modifying the code if I have to. The application is written in VBA (and hence my inclination to avoid touching it). We've noticed that the application seems to run pretty smoothly if we set the processor affinity to a single processor using task manager, only manifesting instability when processor affinity isn't set. I know that I can specify the processor affinity of a task using .NET and as such, there lies a possibility of me writing a shell application that could be used to run legacy applications with a specified processor affinity, does anyone have any experience with this and can throw out some ideas as to headaches I'm likely to run into with this approach? The other question is: Is it in fact possible to modify the core VBA product to handle its own processor affinity? I've never had to handle this with any of my applications natively so this (at this point in time) is completely outside my realm of expertise. Thanks in advance

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• google maps api keys to be set webserver-wide, (as env var? inside apache?)

  - by ~knb

  I have a web site with many virtual hosts and each registered with several domain names (ending in .org, .de), site1.mysite.de, site2.mysite.org Then I have different templating systems based on several programming languages (perl and php) in use on the web server. The Google Maps Api requires a unique Google Maps api key for each vhost. I want to have something like a web-server wide variable $goomapkey that I can call from inside my code. In PHP code, Now I have a kludgy case-analysis solution like $domain = substr($_SERVER['SERVER_NAME'], -3); if (".de" == $domain){ //if ("xxxxxx" eq substr($ENV{SERVER_NAME}, 0, 5)){ // $gookey = "ABQIAAA..."; //} else { //site1.de $gookey = "ABQIAAAA1Js..."; //} } elseif ("dev" == substr($_SERVER['SERVER_NAME'], 0, 3)){ //dev.mysite.org $gookey = "ABQIAAAA1JsSb..."; } else { //www.mysite.org $gookey = "ABQIAAAA1JsS..."; //TODO: Add more keys for each virtual host, for my.machinename.de, IP-address based URL, ... } ... inside my php-based CMS. A non-ideal solution, because it is, php-only, and I still have to set it at several html templates inside the CMS, and there are too many cases. I want the google maps api key to be set by the apache web server who examines the request *early in the request loop before any php page template code is constructed and evaluated. is an environment variable a good solution? which technology should be used to set the $goomapkey variable? I'd prefer mod_perl2 Apache request handler, but the documentation is confusing (many API changes in the past ). Which Apache module could I use? Is there a built-in Apache module that does the same thing?

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• Are there any NOSQL-compatible CMS projects?

  - by Michael

  This question is partially related to an older question (Any CMS is Google App Engine compatible?) , but is slightly more general. It seems that in most CMS systems, the most fragile failure point is the database. Traditional database implementations scale poorly and will never be able to handle unforeseen spikes of traffic. Since Google App Engine was designed to help even small businesses overcome that problem, I had the same question that was asked earlier this year with less than satisfactory answers. But more generally, where are the CMS projects that support NOSQL databases? Looking over Wikipedia's list of CMS platforms, I see without much effort that only traditional RDBMS are supported by every single vendor on the list. I would have expected to see at least one or two projects handling CouchDB or similar engines. I understand the complexities of implementing a NOSQL solution to a problem that is typically solved using the relations cleanly expressed in any RDBMS, but there seems to be a rather wide market gap. Since databases are, today, easily outsourced to Google, Amazon, and others which use NOSQL models, I am amazed that there are not more projects actively pursuing this path. Am I simply not aware? Can someone please point me to projects that have real momentum that are developing on this path? I'm looking for two things: a CMS that has as its backbone a NOSQL database enabling easy database outsourcing (hosted MySQL clusters and similar solutions are not what I'm looking for) a project that is built to run on either a PaaS architecture like Google App Engine or an IaaS architecture like Amazon EC2 Any pointers in that direction would be most welcome.

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• System Calls in windows & Native API?

  - by claws

  Recently I've been using lot of Assembly language in *NIX operating systems. I was wondering about the windows domain. Calling convention in linux: mov $SYS_Call_NUM, %eax mov $param1 , %ebx mov $param2 , %ecx int $0x80 Thats it. That is how we should make a system call in linux. Reference of all system calls in linux: Regarding which $SYS_Call_NUM & which parameters we can use this reference : http://docs.cs.up.ac.za/programming/asm/derick_tut/syscalls.html OFFICIAL Reference : http://kernel.org/doc/man-pages/online/dir_section_2.html Calling convention in Windows: ??? Reference of all system calls in Windows: ??? Unofficial : http://www.metasploit.com/users/opcode/syscalls.html , but how do I use these in assembly unless I know the calling convention. OFFICIAL : ??? If you say, they didn't documented it. Then how is one going to write libc for windows without knowing system calls? How is one gonna do Windows Assembly programming? Atleast in the driver programming one needs to know these. right? Now, whats up with the so called Native API? Is Native API & System calls for windows both are different terms referring to same thing? In order to confirm I compared these from two UNOFFICIAL Sources System Calls: http://www.metasploit.com/users/opcode/syscalls.html Native API: http://undocumented.ntinternals.net/aindex.html My observations: All system calls are beginning with letters Nt where as Native API is consisting of lot of functions which are not beginning with letters Nt. System Call of windows are subset of Native API. System calls are just part of Native API. Can any one confirm this and explain.

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• unbuffered I/O in Linux

  - by stuck

  I'm writing lots and lots of data that will not be read again for weeks - as my program runs the amount of free memory on the machine (displayed with 'free' or 'top') drops very quickly, the amount of memory my app uses does not increase - neither does the amount of memory used by other processes. This leads me to believe the memory is being consumed by the filesystems cache - since I do not intend to read this data for a long time I'm hoping to bypass the systems buffers, such that my data is written directly to disk. I dont have dreams of improving perf or being a super ninja, my hope is to give a hint to the filesystem that I'm not going to be coming back for this memory any time soon, so dont spend time optimizing for those cases. On Windows I've faced similar problems and fixed the problem using FILE_FLAG_NO_BUFFERING|FILE_FLAG_WRITE_THROUGH - the machines memory was not consumed by my app and the machine was more usable in general. I'm hoping to duplicate the improvements I've seen but on Linux. On Windows there is the restriction of writing in sector sized pieces, I'm happy with this restriction for the amount of gain I've measured. is there a similar way to do this in Linux?

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• Continuous build infrastructure recommendations for primarily C++; GreenHills Integrity

  - by andersoj

  I need your recommendations for continuous build products for a large (1-2MLOC) software development project. Characteristics: ClearCase revision control Approx 80% C++; 15% Java; 5% script or low-level Compiles for Green Hills Integrity OS, but also some windows and JVM chunks Mostly an embedded system; also includes some UI pieces and some development support (simulation tools, config tools, etc...) Each notional "version" of the deliverable includes deployment images for a number of boards, UI machines, etc... (~10 separate images; 5 distinct operating systems) Need to maintain/track many simultaneous versions which, notably, are built for a variety of different board support packages Build cycle time is a major issue on the project, need support for whatever features help address this (mostly need to manage a large farm of build machines, I guess..) Operates in a secure environment (this is a gov't program) (Edited to add: This is a classified program; outsourcing the build infrastructure is a non-starter.) Interested in any best practices or peripheral guidance you might offer. The build automation issues is one of several overlapping best practices that appear to be missing on the program, but try to keep your answers focused on build infrastructure piece and observations directly related. Cost is not an object. Scalability and ease of retrofitting onto an existing infrastructure are key. JA

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• My project is no longer used - how should I feel?

  - by flybywire

  For the last two years I have been developing and supporting an important project for a big customer. The project included mining data from the customer's existing systems, processing, and displaying and updating in the customer's public home page. The project was defined as crucial by the customer and I was payed good money and flown at the customer's expense to meet key employees. Some months ago, when the project was finished and in maintainance mode, I informed the customer that I am no longer interested in doing it as I had a new opportunity that would not be compatible with my existing customer. I was payed to train one of their employees, flown to meet him, make sure everything works and that he can be safely left in charge of the project. We finished in good terms after I complied with all my obligations and they payed me all they owed me. Some days ago, just out of curiosity, I entered to their website to see how the data continues to be updated and much to my dismay I discovered that the day after my contract was finished my system was "turned off" and it ceased to feed data to the public website. Let's put it clear, there is no issue of money or broken contract here. They are in they full right to do whatever they want with my software. But it is an issue of broken "programmer's ego". Should I feel bad about it (I do). Should I care and check out with my customer if they need some help? Or is it none of my matters?

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• Connection Pool Strategy: Good, Bad or Ugly?

  - by Drew

  I'm in charge of developing and maintaining a group of Web Applications that are centered around similar data. The architecture I decided on at the time was that each application would have their own database and web-root application. Each application maintains a connection pool to its own database and a central database for shared data (logins, etc.) A co-worker has been positing that this strategy will not scale because having so many different connection pools will not be scalable and that we should refactor the database so that all of the different applications use a single central database and that any modifications that may be unique to a system will need to be reflected from that one database and then use a single pool powered by Tomcat. He has posited that there is a lot of "meta data" that goes back and forth across the network to maintain a connection pool. My understanding is that with proper tuning to use only as many connections as necessary across the different pools (low volume apps getting less connections, high volume apps getting more, etc.) that the number of pools doesn't matter compared to the number of connections or more formally that the difference in overhead required to maintain 3 pools of 10 connections is negligible compared to 1 pool of 30 connections. The reasoning behind initially breaking the systems into a one-app-one-database design was that there are likely going to be differences between the apps and that each system could make modifications on the schema as needed. Similarly, it eliminated the possibility of system data bleeding through to other apps. Unfortunately there is not strong leadership in the company to make a hard decision. Although my co-worker is backing up his worries only with vagueness, I want to make sure I understand the ramifications of multiple small databases/connections versus one large database/connection pool.

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• Void* array casting to float, int32, int16, etc.

  - by Griffin

  Hey guys, I've got an array of PCM data, it could be 16 bit, 24 bit packed, 32 bit, etc.. It could be signed, or unsigned, and it could be 32 or 64 bit floating point. It is currently stored as a "void**" matrix, indexed by channel, then by frame. The goal is to allow my library to take in any PCM format and buffer it, without requiring manipulation of the data to fit a designated structure. If the A/D converter spits out 24 bit packed arrays of interleaved PCM, I need to accept it gracefully. I also need to support 16 bit non interleaved, as well as any permutation of the above formats. I know the bit depth and other information at runtime, and I'm trying to code efficiently while not duplicating code. What I need is an effective way to cast the matrix, put PCM data into the matrix, and then pull it out later. I can cast the matrix to int32_t, or int16_t for the 32 and 16 bit signed PCM respectively, I'll probably have to store the 24 bit PCM in an int32_t for 32 bit, 8 bit byte systems as well. Can anyone recommend a good way to put data into this array, and pull it out later? I'd like to avoid large sections of code which look like: switch( mFormat ) { case 1: // unsigned 8 bit for( int i = 0; i < mChannels; i++ ) framesArray = (uint8_t*)pcm[i]; break; case 2: // signed 8 bit for( int i = 0; i < mChannels; i++ ) framesArray = (int8_t*)pcm[i]; break; case 3: // unsigned 16 bit ... Limitations: I'm working in C/C++, no templates, no RTTI, no STL. Think embedded. Things get trickier when I have to port this to a DSP with 16 bit bytes. Does anybody have any useful macros they might be willing to share? Thanks, -Griff

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• File size monitoring in C#

  - by manemawanna

  Hello, I work in the Systems & admin team and have been given the task of creating a quota management application to try and encourage users to better manage there resources as we currently have issues with disc space and don't enforce hard quotas. At the moment I'm using the code below to go through all the files in a users homespace to retrieve the overall amount of space they are using. As from what I've seen else where theres no other way to do this in C#, the issue with it is theirs quite a high overhead while it retireves the size of each file then creates a total. try { long dirSize = 0; FileInfo[] FI = new DirectoryInfo("I:\\").GetFiles("*.*", SearchOption.AllDirectories); foreach (FileInfo F1 in FI) { dirSize += F1.Length; } return dirSize; } So I'm looking for a quicker way to do this or a quick way to monitor changes in the size of files while using the options avaliable through FileSystemWatcher. At the moment the only thing I can think of is creating a hashtable containing the file location and size of each file, so when a size changed event occurs I can compare the old size against the new one and update the total. Any suggestions would be greatly appreciated.

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• Better language or checking tool?

  - by rwallace

  This is primarily aimed at programmers who use unmanaged languages like C and C++ in preference to managed languages, forgoing some forms of error checking to obtain benefits like the ability to work in extremely resource constrained systems or the last increment of performance, though I would also be interested in answers from those who use managed languages. Which of the following would be of most value? A language that would optionally compile to CLR byte code or to machine code via C, and would provide things like optional array bounds checking, more support for memory management in environments where you can't use garbage collection, and faster compile times than typical C++ projects. (Think e.g. Ada or Eiffel with Python syntax.) A tool that would take existing C code and perform static analysis to look for things like potential null pointer dereferences and array overflows. (Think e.g. an open source equivalent to Coverity.) Something else I haven't thought of. Or put another way, when you're using C family languages, is the top of your wish list more expressiveness, better error checking or something else? The reason I'm asking is that I have a design and prototype parser for #1, and an outline design for #2, and I'm wondering which would be the better use of resources to work on after my current project is up and running; but I think the answers may be useful for other tools programmers also. (As usual with questions of this nature, if the answer you would give is already there, please upvote it.)

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• complex regular expression task

  - by Don Don

  Hi, What regular expressions do I need to extract section title(s) in a text file? So, in the following sample text, I'd like to extract "Communication and Leadership" "1.Self-Knowledge" "2. Humility" "(3) Clear Thinking". Many thanks. Communication and Leadership True leaders understand that, rather than forcing their followers into a preconceived mold, their job is to motivate and organize followers to collectively accomplish goals that are in everyone's interests. The ability to communicate this to co-workers and followers is critical to the effectiveness of leadership. 1.Self-Knowledge Superior leaders are able to devote their skills and energies to leadership of a group because they have worked through personal issues to the point where they know themselves thoroughly. A high level of self-knowledge is a prerequisite to effective communication skills, because the things that you communicate as a leader are coming from within. 2. Humility This subversion of personal preference requires a certain level of humility. Although popular definitions of leaders do not always see them as humble, the most effective leaders actually are. This humility may not be expressed in self-effacement, but in a total commitment to the goals of the organization. Humility requires an understanding of one's own relative unimportance in comparison to larger systems. (3) Clear Thinking Clarity of thinking translates into clarity of communication. A leader whose goals or personal analysis is muddled will tend to deliver unclear or ambiguous directions to followers, leading to confusion and dissatisfaction. A leader with a clear mind who is not ambivalent about her purposes will communicate what needs to be done in a s traightforward and unmistakable manner.

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• What can cause a spontaneous EPIPE error without either end calling close() or crashing?

  - by Hongli

  I have an application that consists of two processes (let's call them A and B), connected to each other through Unix domain sockets. Most of the time it works fine, but some users report the following behavior: A sends a request to B. This works. A now starts reading the reply from B. B sends a reply to A. The corresponding write() call returns an EPIPE error, and as a result B close() the socket. However, A did not close() the socket, nor did it crash. A's read() call returns 0, indicating end-of-file. A thinks that B prematurely closed the connection. Users have also reported variations of this behavior, e.g.: A sends a request to B. This works partially, but before the entire request is sent A's write() call returns EPIPE, and as a result A close() the socket. However B did not close() the socket, nor did it crash. B reads a partial request and then suddenly gets an EOF. The problem is I cannot reproduce this behavior locally at all. I've tried OS X and Linux. The users are on a variety of systems, mostly OS X and Linux. Things that I've already tried and considered: Double close() bugs (close() is called twice on the same file descriptor): probably not as that would result in EBADF errors, but I haven't seen them. Increasing the maximum file descriptor limit. One user reported that this worked for him, the rest reported that it did not. What else can possibly cause behavior like this? I know for certain that neither A nor B close() the socket prematurely, and I know for certain that neither of them have crashed because both A and B were able to report the error. It is as if the kernel suddenly decided to pull the plug from the socket for some reason.

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• C++ RPC library suggestions

  - by Oxsnarder

  I'm looking for suggestions regarding RPC libraries implemented in C++, for C++ developers. Some requirements constraints: Should work on both linux/unix and win32 systems Be able to execute free function and class methods Hopefully written in modern C++ not 90's/java-esque C++ Be able to function over networks and hetrogenous architectures Not too slow or inefficient Hopefully provide interfaces for TR1 style std::function's et al. My example usage is to invoke the free function foo on a remote machine. ---snip--- // foo translation unit int foo(int i, int j) { return i + j; } ---snip--- ---snip--- // client side main int main() { //register foo on client and server //setup necassary connections and states int result; if (RPCmechanism.invoke("foo",4,9,result)) std::cout << "foo(4,9) = " result << std::endl; else std::cout << "failed to invoke foo(4,9)!" << std::endl; return 0; } ---snip--- Something that can achieve the above or similar would be great.

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• A generic C++ library that provides QtConcurrent functionality?

  - by Lucas

  QtConcurrent is awesome. I'll let the Qt docs speak for themselves: QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications. For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system. There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like. I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do). I'm looking for a generic C++ framework that provides me with the same/similar high-level primitives that QtConcurrent does. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for. I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea. What do you suggest I use?

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• data ownership and performance

  - by Ami

  We're designing a new application and we ran into some architectural question when thinking about data ownership. we broke down the system into components, for example Customer and Order. each of this component/module is responsible for a specific business domain, i.e. Customer deals with CRUD of customers and business process centered around customers (Register a n new customer, block customer account, etc.). each module is the owner of a set of database tables, and only that module may access them. if another module needs data that is owned by another module, it retrieves it by requesting it from that module. so far so good, the question is how to deal with scenarios such as a report that needs to show all the customers and for each customer all his orders? in such a case we need to get all the customers from the Customer module, iterate over them and for each one get all the data from the Order module. performance won't be good...obviously it would be much better to have a stored proc join customers table and orders table, but that would also mean direct access to the data that is owned by another module, creating coupling and dependencies that we wish to avoid. this is a simplified example, we're dealing with an enterprise application with a lot of business entities and relationships, and my goal is to keep it clean and as loosely coupled as possible. I foresee in the future many changes to the data scheme, and possibly splitting the system into several completely separate systems. I wish to have a design that would allow this to be done in a relatively easy way. Thanks!

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