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• How do I prevent my filesystems from being mounted read-only after suspending?

  - by Chas. Owens

  I have Ubuntu 12.04 installed on an SDHC card (only one ext2 partition, no swap). When I suspend using pm-suspend, my root filesystem is mounted read-only. I am currently "fixing" this with the following file: /etc/pm/sleep.d/99_make_disk_rw: #!/bin/sh mount -o remount,rw / But the disk is marked as needing an fsck on reboot. How can I prevent the filesystem from being mounted read-only or whatever is going wrong here. Update: It looks like it is getting mounted read-only because an error occurred. I have changed the mount options for / in /etc/fstab to noatime,nodiratime,errors=continue and it no longer mounts the SDHC card as read-only after it resumes. So the problem is happening when it suspends, not when it resumes as I had thought. I checked /sys/bus/usb/devices/1-4/power/persist and it is set to 1. So the SDHC card shouldn't appear disconnected to the OS (or more accurately it should recover from the disconnection without error). Here seems to be the relevant section of the syslog Sep 10 10:34:23 iubit kernel: [ 748.246226] sd 4:0:0:0: [sdb] Media Changed Sep 10 10:34:23 iubit kernel: [ 748.246234] sd 4:0:0:0: [sdb] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE Sep 10 10:34:23 iubit kernel: [ 748.246243] sd 4:0:0:0: [sdb] Sense Key : Unit Attention [current] Sep 10 10:34:23 iubit kernel: [ 748.246253] Info fld=0x0 Sep 10 10:34:23 iubit kernel: [ 748.246258] sd 4:0:0:0: [sdb] Add. Sense: Not ready to ready change, medium may have changed Sep 10 10:34:23 iubit kernel: [ 748.246271] sd 4:0:0:0: [sdb] CDB: Read(10): 28 00 00 5d 3e f0 00 00 08 00 Sep 10 10:34:23 iubit kernel: [ 748.246291] end_request: I/O error, dev sdb, sector 6110960 Sep 10 10:34:23 iubit kernel: [ 748.247027] EXT2-fs (sdb1): error: ext2_fsync: detected IO error when writing metadata buffers Sep 10 10:34:23 iubit anacron[6954]: Anacron 2.3 started on 2012-09-10 Sep 10 10:34:23 iubit anacron[6954]: Normal exit (0 jobs run) Sep 10 10:34:24 iubit laptop-mode: Laptop mode Sep 10 10:34:24 iubit laptop-mode: enabled, not active Sep 10 10:34:24 iubit kernel: [ 749.055376] sd 4:0:0:0: [sdb] No Caching mode page present Sep 10 10:34:24 iubit kernel: [ 749.055387] sd 4:0:0:0: [sdb] Assuming drive cache: write through Sep 10 10:34:25 iubit anacron[7555]: Anacron 2.3 started on 2012-09-10 Sep 10 10:34:25 iubit anacron[7555]: Normal exit (0 jobs run) Sep 10 10:34:31 iubit kernel: [ 756.090861] EXT2-fs (sdb1): previous I/O error to superblock detected

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• git for personal (one-man) projects. Overkill?

  - by Anto

  I know, and use, two version control systems: Subversion and git. Subversion, as of now, gets used for personal projects where I am the only developer and git gets used for open source projects and projects where I believe others will also work on the project. This is mostly because of git's amazing forking and merging capabilities, where everyone may work on their own branch; very handy. Now, I use Subversion for personal projects, as I think git makes little sense there. It seems to be a little bit of overkill. It is OK for me if it is centralized (on my home server, usually) when I am the only developer; I take regular backups anyway. I don't need the ability to make my own branch, the main branch is my branch. Yes, SVN has simple support for branching, but much more powerful support for it makes no sense, I think. Merging can be a pain with it, or at least from my little experience. Is there any good reason for me to use git on personal projects, or is it just simply overkill?

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• Is these company terms good for a programmer or should I move?

  - by o_O

  Here are some of the terms and conditions set forward by my employer. Does these make sense for a job like programming? No freelancing in any way even in your free time outside company work hours (may be okay. May be they wanted their employees to be fully concentrating on their full time job. Also they don't want their employees to do similar work for a competing client. Completely rational in that sense). - So sort of agreed. Any thing you develop like ideas, design, code etc while I'm employed there, makes them the owner of that. Seriously? Don't you think that its bad (for me)? If I'm to develop something in my free time (by cutting down sleep and hard working), outside the company time and resource, is that claim rational? I heard that Steve Wozniak had such a contract while he was working at HP. But that sort of hardware design and also those companies pay well, when compared to the peanuts I get. No other kind of works allowed. Means no open source stuffs. Fully dedicated to being a puppet for the employer, though the working environment is sort of okay. According to my assessment this place would score a 10/12 in Joel's test. So are these terms okay especially considering the fact that I'm underpaid with peanuts?

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• Are these company terms good for a programmer or should I move?

  - by o_O

  Here are some of the terms and conditions set forward by my employer. Does these make sense for a job like programming? No freelancing in any way even in your free time outside company work hours (may be okay. May be they wanted their employees to be fully concentrating on their full time job. Also they don't want their employees to do similar work for a competing client. Completely rational in that sense). - So sort of agreed. Any thing you develop like ideas, design, code etc while I'm employed there, makes them the owner of that. Seriously? Don't you think that its bad (for me)? If I'm to develop something in my free time (by cutting down sleep and hard working), outside the company time and resource, is that claim rational? I heard that Steve Wozniak had such a contract while he was working at HP. But that sort of hardware design and also those companies pay well, when compared to the peanuts I get. No other kind of works allowed. Means no open source stuffs. Fully dedicated to being a puppet for the employer, though the working environment is sort of okay. According to my assessment this place would score a 10/12 in Joel's test. So are these terms okay especially considering the fact that I'm underpaid with peanuts?

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• Prepared statement alternatives for this middle-man program?

  - by user2813274

  I have an program that is using a prepared statement to connect and write to a database working nicely, and now need to create a middle-man program to insert between this program and the database. This middle-man program will actually write to multiple databases and handle any errors and connection issues. I would like advice as to how to replicate the prepared statements such as to create minimal impact to the existing program, however I am not sure where to start. I have thought about creating a "SQL statement class" that mimics the prepared statement, only that seems silly. The existing program is in Java, although it's going to be networked anyways so I would be open to writing it in just about anything that would make sense. The databases are currently MySQL, although I would like to be open to changing the database type in the future. My main question is what should the interface for this program look like, and does doing this even make sense? A distributed DB would be the ideal solution, but they seem overly complex and expensive for my needs. I am hoping to replicate the main functionality of a distributed DB via this middle-man. I am not too familiar with sql-based servers distributing data (or database in general...) - perhaps I am fighting an uphill battle by trying to solve it via programming, but I would like to make an attempt at least.

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• Sorting objects before rendering

  - by dreta

  I'm trying to implement a scene graph and in all the articles i've come across there is talk about object sorting. So you'd sort your objects by "material" for example. Now untill i sat down and started implementing it, i kind of took this for granted, because it made sense. But now i'm wondering what does sorting actually change? In my engine, i have a manager for UBOs, i use those to store data that'll be shared between programs, at the moment that only involves time, camera and projection matrices and lights (i'm not worrying about managing which lights affect which objects ATM). Now for each model i have to change the model to world matrix uniform, no sorting is going to change that. So is the jump from changing this matrix to also setting a material for each object that bad? I vaguely remember reading somewhere that each time you change something in the pipeline, it has to get flushed and that can cause performance issues. But for each drawing call i'm setting up a model to world matrix anyway, so what sense does it make to ever be concerned about this? BTW is there any information about whether changing a uniform and calling glBufferSubData is more (or less) expensive.

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• Rule of thumb for cost vs. savings for code re-use

  - by Styler

  Is it a good rule of thumb to always write code for the intent of re-using it somewhere down the road? Or, depending on the size of the component you are writing, is it better practice to design it for re-use when it makes sense with regards to time spent on it. What is a good rule of thumb for spending extra time on analysis and design on project components that have "some probability" of being needed later down the road for other things that may or may need this part. For example, if I have the need for project X to do things A, and B. A definitely needs to be written for re-use because it just makes sense to do so. B is very project specific at the moment, and I can hack it all together in a couple days to finish the project on time and give everyone kudos for being a great team, etc. Or if we say, lets spend a whole friggin' 2 weeks figuring out what project Y/Z might need this thing for and spend a load of extra time on on part B because someday we might need to use it on project Y/Z (where the savings will be realized). I'd imagine a perfect world situation would be a nicely crafted combination of project specific vs. re-use architected components given the project. However some code shops might feel it would be a great idea to write everything for the intention of using it at some point down the road.

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• Tomcat + Spring + CI workflow

  - by ex3v

  We're starting our very first project with Spring and java web stack. This project will be mainly about rewriting quite large ERP/CRM from Zend Framework to Java. Important factor in my question is that I come from php territory, where things (in terms of quality) tend to look different than in java world. Fatcs: there will be 2-3 developers, at least one of developers uses Windows, rest uses Linux, there is one remote linux-based machine, which should handle test and production instances, after struggling with buggy legacy code, we want to introduce good programming and development practices (CI, tests, clean code and so on) client: internal, frequent business logic changes, scrum, daily deployments What I want to achieve is good workflow on as many development stages as possible (coding - commiting - testing - deploying). The problem is that I've never done this before, so I don't know what are best practices to do this. What I have so far is: developers code locally, there is vagrant instance on every development machine, managed by puppet. It contains the same linux, jenkins and tomcat versions as production machine, while coding, developer deploys to vagrant machine, after local merge to test branch, jenkins on vagrant handles tests, when everything is fine, developer pushes commits and merges jenkins on remote machine pulls commit from test branch, runs tests and so on, if everything looks green, jenkins deploys to test tomcat instance Deployment to production is manual (altough it can be done using helping scripts) when business logic is tested by other divisions and everything looks fine to client. Now, the real question: does above make any sense? Things that I'm not sure about: Remote machine: won't there be any problems with two (or even three, as jenkins might need one) instances of same app on tomcat? Using vagrant to develop on php environment is just vise. Isn't this overkill while using Tomcat? I mean, is there higher probability that tomcat will act the same on every machine? Is there sense of having local jenkins on vagrant?

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• Where to Start?

  - by freemann098

  my name is Chase. I've been programming for over 3 years now and I've made very little progress towards game development. I blame myself for it due to reasons. I have experience in many languages such as C++, C#, and Java. I have a little bit of knowledge in JavaScript/HTML and Python. My question is where to start on actually understanding jumping into game development. Whenever I watch game development tutorials it mostly makes sense until points of things like OpenGL or advanced topics that make no sense at all. An example is something like glOrhho Matrix or whatever. Videos either don't explain things like this or they're not explained very well. Do I not know enough basics? I find myself always copying code from a video but understanding very little of it. It's like i'm memorizing things I don't understand which makes it hard to program at all. If I were to want to get to the point where I could write my own game engine or just a game by myself in general in C++ using at the most documentation how would I start at mastering to that level. Should I learn C first, or get really good at basics in general with C++. I know there is a similar posted question on this site but it's not the same due to the fact the person asking the question has a well knowledge level in programming. I'm stuck in a loop of learning the same things but if I go farther I don't understand. I'm stuck in the same spot and need to make progress.

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• Where is Oracle Utilities Application Framework V3?

  - by Anthony Shorten

  You may of noticed that the latest version of the Oracle Utilities Application Framework is V4.0.1. The last release of the Framework was V2.2. So what happened to V3? The short answer is that there is no V3 of the framework. The long answer is that the Oracle Utilities Application Framework has long been associated with Oracle Utilities Customer Care And Billing and Oracle Enterprise Taxation Management only. As more and more of the Oracle Tax And Utilities products are migrated onto the framework the association betweent eh original products on the framework is less appropriate. Therefore it was decided to pick a version number to emphasize the decouplinf of the releases of the Framework with any particular product. To illustrate this, the Oracle Mobile Workforce Management (MWM) V2.0.0 product uses Oracle Utilities Applicaton Framework V4.0.1. If we used the old numberings schema then MWM would be V4.0.1 which makes no sense, given the last release of MWM was V1.x The framework has its own development team and product management. It basicaly has its own schedule (though it is influenced by the products that use it still - which makes sense). So that s the reasoning around the version numbering change for the framework.

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• Query something and return the reason if nothing has been found

  - by Daniel Hilgarth

  Assume I have a Query - as in CQS that is supposed to return a single value. Let's assume that the case that no value is found is not exceptional, so no exception will be thrown in this case. Instead, null is returned. However, if no value has been found, I need to act according to the reason why no value has been found. Assuming that the Query knows the reason, how would I communicate it to the caller of the Query? A simple solution would be not return the value directly but a container object that contains the value and the reason: public class QueryResult { public TValue Value { get; private set; } public TReason ReasonForNoValue { get; private set; } } But that feels clumsy, because if a value is found, ReasonForNoValue makes no sense and if no value has been found, Value makes no sense. What other options do I have to communicate the reason? What do you think of one event per reason? For reference: This is going to be implemented in C#.

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• "Programming error" exceptions - Is my approach sound?

  - by Medo42

  I am currently trying to improve my use of exceptions, and found the important distinction between exceptions that signify programming errors (e.g. someone passed null as argument, or called a method on an object after it was disposed) and those that signify a failure in the operation that is not the caller's fault (e.g. an I/O exception). As far as I understand, it makes little sense for an immediate caller to actually handle programming error exceptions, he should instead assure that the preconditions are met. Only "outer" exception handlers at task boundaries should catch them, so they can keep the system running if a task fails. In order to ensure that client code can cleanly catch "failure" exceptions without catching error exceptions by mistake, I create my own exception classes for all failure exceptions now, and document them in the methods that throw them. I would make them checked exceptions in Java. Now I have a few questions: Before, I tried to document all exceptions that a method could throw, but that sometimes creates an unwiedly list that needs to be documented in every method up the call chain until you can show that the error won't happen. Instead, I document the preconditions in the summary / parameter descriptions and don't even mention what happens if they are not met. The idea is that people should not try to catch these exceptions explicitly anyway, so there is no need to document their types. Would you agree that this is enough? Going further, do you think all preconditions even need to be documented for every method? For example, calling methods in IDisposable objects after calling Dispose is an error, but since IDisposable is such a widely used interface, can I just assume a programmer will know this? A similar case is with reference type parameters where passing null makes no conceivable sense: Should I document "non-null" anyway? IMO, documentation should only cover things that are not obvious, but I am not sure where "obvious" ends.

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• Modular Web App Network Architecture

  - by nairware

  Assuming that I am dealing with dedicated physical servers or VPSs, is it conceivable and does it make sense to have distinct servers setup with the following roles to host a web application? Reverse Proxy Web server Application server Database server Specific points of interest: I am confused how to even separate the web and application servers. My understanding was that such 3-tier architectures were feasible. It is unclear to me if the app server would reside directly between the web and database server, or if the web server could directly interact with the database as well. The app server could either do the computational heavy-lifting on behalf of the app server or it could do heavy-lifting plus control all of the business logic (as implied in the diagram above, thus denying the web server of direct database access). I am also unsure what role the reverse proxy (ex. nginx) could and should fulfill as a web server, given the above mentioned setup. I know that nginx has web server features. But I do not know if it makes sense to have the reverse proxy be its own VPS, given that the web server–in theory–would be separate from the app server.

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• Are DDD Aggregates really a good idea in a Web Application?

  - by Mystere Man

  I'm diving in to Domain Driven Design and some of the concepts i'm coming across make a lot of sense on the surface, but when I think about them more I have to wonder if that's really a good idea. The concept of Aggregates, for instance makes sense. You create small domains of ownership so that you don't have to deal with the entire domain model. However, when I think about this in the context of a web app, we're frequently hitting the database to pull back small subsets of data. For instance, a page may only list the number of orders, with links to click on to open the order and see its order id's. If i'm understanding Aggregates right, I would typically use the repository pattern to return an OrderAggregate that would contain the members GetAll, GetByID, Delete, and Save. Ok, that sounds good. But... If I call GetAll to list all my order's, it would seem to me that this pattern would require the entire list of aggregate information to be returned, complete orders, order lines, etc... When I only need a small subset of that information (just header information). Am I missing something? Or is there some level of optimization you would use here? I can't imagine that anyone would advocate returning entire aggregates of information when you don't need it. Certainly, one could create methods on your repository like GetOrderHeaders, but that seems to defeat the purpose of using a pattern like repository in the first place. Can anyone clarify this for me?

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• USB flash module giving errors

  - by vshenoy

  Hi, I have a SATA USB flash module which was earlier running a 2.4 linux kernel (2.4.36.6) and on which now I am trying to install ubuntu server 10.04.1 LTS. I have two such USB flash modules and on one of them the installation process itself giving these errors: sd 4:0:0:0 [sda] Device not ready sd 4:0:0:0 [sda] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE sd 4:0:0:0 [sda] Sense Key : Not Ready [current] sd 4:0:0:0 [sda] Add. Sense: Medium not present sd 4:0:0:0 [sda] CDB: Write(10): 2a 00 00 05 48 02 00 00 04 00 end_request: I/O error, dev sda, sector 46114 usb 1-1: reset high speed USB device using ehci_hcd and address 2 Buffer I/O error on device sda1, logical block 172033 lost page write due to I/O error on sda1 Buffer I/O error on device sda1, logical block 172034 lost page write due to I/O error on sda1 on the other the installation is successful, but after a day or two of running the machine hangs because of kernel spewing these messages: Remounting filesystem read-only EXT2-fs error (device sda1): read_block_bitmap: Cannot read block [bitmap - block_group = 105, block_bitmap = 860161] EXT2-fs error (device sda1): ext2_get_inode: unable to read inode block - inode=13083, block=24683 ext2_free_inode: bit already cleared for inode 83966 and the machine needs to be hard rebooted. On both the systems SCSI emulation with usb_storage driver is being used to detect the module. Here is the output of /proc/scsi/scsi on 2.4: # cat /proc/scsi/scsi Attached devices: Host: scsi0 Channel: 00 Id: 00 Lun: 00 Vendor: TS Model: UFM Rev: 1100 Type: Direct-Access ANSI SCSI revision: 02 and on 2.6: # cat /proc/scsi/scsi Attached devices: Host: scsi6 Channel: 00 Id: 00 Lun: 00 Vendor: TS Model: UFM Rev: 1100 Type: Direct-Access ANSI SCSI revision: 00 i.e. only 'ANSI SCSI revision:' is shown as different, although I am not sure if this can cause any problem. Really appreciate if someone can point as to how to debug this issue or any mailing list where I can further ask questions about this.

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• To Virtual or Not to Virtual

  - by Kevin Shyr

  I recently made a comment "I hate everything virtual" while responding to a SQL server performance question.  I then promptly fired up my Hyper-V development environment to do my proof of concept stuff, and realized that I made the cardinal sin of making a generalized comment about something, instead of saying "It depends". The bottom line is if the virtual environment gives the throughput that the server needs, then it is not that big of a deal.  I just have seen so many environment set up with SQL server sitting in virtual environment sitting in a SAN, so on top of having to plan for loss data, I now have to plan for my virtual environment failing for so many different reasons, thought SQL 2012 High Availability Group should make that easier.  To me, a virtual environment makes sense for a stateless application with big scalibility requirement, but doesn't give much benefit to an application where performance and data integrity are both important.  If security is not a concern, I would just build servers with multiple instances on them to balance the workload. Maybe this is also too generalized a comment, and I'll confess that I'm not a DBA by trade.  I'd love to hear the pros and cons of virtualizing a SQL server, or other examples where virtualization makes total sense (not just money, but recovery, rollback, etc.)

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• TXPAUSE : polite waiting for hardware transactional memory

  - by Dave

  Classic locks are an appropriate tool to prevent potentially conflicting operations A and B, invoked by different threads, from running at the same time. In a sense the locks cause either A to run before B or vice-versa. Similarly, we can replace the locks with hardware transactional memory, or use transactional lock elision to leverage potential disjoint access parallelism between A and B. But often we want A to wait until B has run. In a Pthreads environment we'd usually use locks in conjunction with condition variables to implement our "wait until" constraint. MONITOR-MWAIT is another way to wait for a memory location to change, but it only allows us to track one cache line and it's only available on x86. There's no similar "wait until" construct for hardware transactions. At the instruction-set level a simple way to express "wait until" in transactions would be to add a new TXPAUSE instruction that could be used within an active hardware transaction. TXPAUSE would politely stall the invoking thread, possibly surrendering or yielding compute resources, while at the same time continuing to track the transaction's address-set. Once a transaction has executed TXPAUSE it can only abort. Ideally that'd happen when some other thread modifies a variable that's in the transaction's read-set or write-set. And since we're aborting all writes would be discarded. In a sense this gives us multi-location MWAIT but with much more flexibility. We could also augment the TXPAUSE with a cycle-count bound to cap the time spent stalled. I should note that we can already enter a tight spin loop in a transaction to wait for updates to address-set to cause an abort. Assuming that the implementation monitors the address-set via cache-coherence probes, by waiting in this fashion we actually communicate via the probes, and not via memory values. That is the updating thread signals the waiter via probes instead of by traditional memory values. But TXPAUSE gives us a polite way to spin.

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• How do I draw a 2d plane and rotate camara (To be a board) in a 3d XNA game?

  - by Mech0z

  I am trying to create a simple board game, but the 3d part of this is really killing me. From what I can gather I have created a plane, but it never moves even though I turn the camara, but that partially makes sense as I only turn the camara with a 3d model, but in my head that makes 0 sense, in my head if I turn the camara it should affect ALL my models? But with this code the camara only "cares" about the 3d cylinder, the plane is just completely still private void OnDraw(object sender, GameTimerEventArgs e) { SharedGraphicsDeviceManager.Current.GraphicsDevice.Clear(Color.CornflowerBlue); foreach (ModelMesh mesh in cylinderModel.Meshes) { foreach (BasicEffect effect in mesh.Effects) { //effect.World = Matrix.CreateRotationX((float)e.TotalTime.TotalSeconds * 2); effect.View = Matrix.CreateLookAt(cameraPosition, Vector3.Zero, Vector3.Up); effect.Projection = Matrix.CreatePerspectiveFieldOfView(MathHelper.ToRadians(45.0f), aspectRatio, 1.0f, 10000.0f); effect.EnableDefaultLighting(); } mesh.Draw(); } //cameraPosition.Z -= 5.0f; _effect.World = Matrix.CreateRotationZ((MathHelper.ToRadians(((float)e.TotalTime.Milliseconds / 2) % 360))); foreach (EffectPass pass in _effect.CurrentTechnique.Passes) { pass.Apply(); SharedGraphicsDeviceManager.Current.GraphicsDevice.DrawUserPrimitives(PrimitiveType.TriangleStrip, _vertices, 0, 1, VertexPositionColor.VertexDeclaration); } } Is there a way to get the camara to affect all models?

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• Do cross reference database tables have a place in domain driven design?

  - by Mike Cellini

  First some background. Let's say we have a system where a customer is placing an order in a web interface. The items that customer is ordering can priced in various ways. Sometimes including the cost of delivery and sometimes not at all. That pricing effectively depends on a variety of factors including the vendor's own pricing model, that vendor's individual contracts with customers as well as that vendor's contracts with its own suppliers. Let's assume that once a customer places an order for a particular item and chooses a contract if any, the method of delivery can be determined by variables on those contracts. Those delivery methods also live in their own table in the database and have various properties consumed downstream. It makes sense that a cross reference or lookup table would store that information. That table would be loaded into the domain and could then be used to apply the appropriate delivery method while processing the order. Does this make sense in the context of domain driven design? Or is my thinking too relational? Is this logic that should be built into it's own class/method (I mean beyond apply the cross reference table data)?

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• ArchBeat Link-o-Rama for November 6, 2012

  - by Bob Rhubart

  OAM/OVD JVM Tuning | @FusionSecExpert Vinay from the Oracle Fusion Middleware Architecture Group (the infamous A-Team) shares a process for analyzing and improving performance in Oracle Virtual Directory and Oracle Access Manager. Architects Matter: Making sense of the people who make sense of enterprise IT Why do architects matter? Oracle Enterprise Architect Eric Stephens suggests that you ask yourself that question the next time you take the elevator to the Oracle offices on the 45th floor of the Willis Tower in Chicago, Illinois (or any other skyscraper, for that matter). If you had to take the stairs to get to those offices, who would you blame? "You get the picture," he says. "Architecture is essential for any necessarily complex structure, be it a building or an enterprise." (Read the article...) SOA Galore: New Books for Technical Eyes Only Shake up up your technical skills with this trio of new technical books from community members covering SOA and BPM. Thought for the Day "It goes against the grain of modern education to teach students to program. What fun is there to making plans, acquiring discipline, organizing thoughts, devoting attention to detail, and learning to be self critical?" — Alan Perlis (April 1, 1922 – February 7, 1990) Source: SoftwareQuotes.com

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• @staticmethod vs module-level function

  - by darkfeline

  This is not about @staticmethod and @classmethod! I know how staticmethod works. What I want to know is the proper use cases for @staticmethod vs. a module-level function. I've googled this question, and it seems there's some general agreement that module-level functions are preferred over static methods because it's more pythonic. Static methods have the advantage of being bound to its class, which may make sense if only that class uses it. However, in Python functionality is usually organized by module not class, so usually making it a module function makes sense too. Static methods can also be overridden by subclasses, which is an advantage or disadvantage depending on how you look at it. Although, static methods are usually "functionally pure" so overriding it may not be smart, but it may be convenient sometimes (though this may be one of those "convenient, but NEVER DO IT" kind of things only experience can teach you). Are there any general rule-of-thumbs for using either staticmethod or module-level functions? What concrete advantages or disadvantages do they have (e.g. future extension, external extension, readability)? If possible, also provide a case example.

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• model association or controller?

  - by andybritton

  I'm trying to create a rails app that allows users to submit information about their pets. I've come to a point where my knowledge is limited and I don't know enough about what/how this could be done so I'm hoping this will be relatively easy to answer. At the moment I have a model called Pet, this model currently stores basic information like name, picture etc but it also holds more specific data like type, breed, date of birth etc. What I would like to be able to do is create a page that can match various records without having to be manually categorized if that makes sense so a users pet could be matched to other pets with the same breed, age etc. I've read about nested models as I understand this information could be submitted to 2 models in one form but I am not sure whether this could be done directly in a separate controller which would only be visible to users with pets in these matched "groups" if that makes sense. So in essence is it best practice to use 1 table to store all the information and just use a controller to match pets based on rows having the same values or would it be far simpler to have a form with a nested model and link 2 tables together? The main feature needs to be matching without a user having to create a group or categorize pets so the second model would need to add id's to an array instead of just creating more and more rows.

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• Scaling sprite velocity / co-ordinatesin Android

  - by user22241

  I'm trying to find the answer to a question that I've had for a long time, but am having trouble finding it! I hope someone can help :-) I'm trying to find information on how to scale sprite velocity / movement / co-ordinates. What I mean by this is how do I get a sprite to move at the same speed relative to the screen size / DPI so that it takes the same amount of real-time to get from one side of the screen to the other? All of the posts pertaining to sprite scaling that I can find on the various forums relate to the size of the sprite, but this part of it I'm OK with so far, it's just that when I move a sprite, it kind of gets there at different speed depending on the dpi / resolution of the device. I hope I'm making sense. This is the code I have so far, instead of using explicit amounts, like 1, I'm using something like the following: platSpeedFloat= (1 * (dpi/160)); //Use '1' so on an MDPI screen, the sprite will move by 1 physical pixel Then basically what I'm doing is something like this: (all varialble previously declared) platSpeedSave+=platSpeedFloat; //Add the platSpeedFloat value to the current platSpeedSave value platSpeed=(int) platSpeedSave; //Cast to int so it can be checked in the following statement if (platSpeed==platSpeedSave) //Check the casted int value to float value stored previoiusly {floorY=floorY-platSpeed; //If they match then change the Y value platSpeedSave=0;} //Reset Would be grateful if someone could assists - hope I'm making sense. The above doesn't seems to work the sprite moves 'faster' on lower DPI screens. Thanks

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• Auto DOP and Concurrency

  - by jean-pierre.dijcks

  After spending some time in the cloud, I figured it is time to come down to earth and start discussing some of the new Auto DOP features some more. As Database Machines (the v2 machine runs Oracle Database 11.2) are effectively selling like hotcakes, it makes some sense to talk about the new parallel features in more detail. For basic understanding make sure you have read the initial post. The focus there is on Auto DOP and queuing, which is to some extend the focus here. But now I want to discuss the concurrency a little and explain some of the relevant parameters and their impact, specifically in a situation with concurrency on the system. The goal of Auto DOP The idea behind calculating the Automatic Degree of Parallelism is to find the highest possible DOP (ideal DOP) that still scales. In other words, if we were to increase the DOP even more  above a certain DOP we would see a tailing off of the performance curve and the resource cost / performance would become less optimal. Therefore the ideal DOP is the best resource/performance point for that statement. The goal of Queuing On a normal production system we should see statements running concurrently. On a Database Machine we typically see high concurrency rates, so we need to find a way to deal with both high DOP’s and high concurrency. Queuing is intended to make sure we Don’t throttle down a DOP because other statements are running on the system Stay within the physical limits of a system’s processing power Instead of making statements go at a lower DOP we queue them to make sure they will get all the resources they want to run efficiently without trashing the system. The theory – and hopefully – practice is that by giving a statement the optimal DOP the sum of all statements runs faster with queuing than without queuing. Increasing the Number of Potential Parallel Statements To determine how many statements we will consider running in parallel a single parameter should be looked at. That parameter is called PARALLEL_MIN_TIME_THRESHOLD. The default value is set to 10 seconds. So far there is nothing new here…, but do realize that anything serial (e.g. that stays under the threshold) goes straight into processing as is not considered in the rest of this post. Now, if you have a system where you have two groups of queries, serial short running and potentially parallel long running ones, you may want to worry only about the long running ones with this parallel statement threshold. As an example, lets assume the short running stuff runs on average between 1 and 15 seconds in serial (and the business is quite happy with that). The long running stuff is in the realm of 1 – 5 minutes. It might be a good choice to set the threshold to somewhere north of 30 seconds. That way the short running queries all run serial as they do today (if it ain’t broken, don’t fix it) and allows the long running ones to be evaluated for (higher degrees of) parallelism. This makes sense because the longer running ones are (at least in theory) more interesting to unleash a parallel processing model on and the benefits of running these in parallel are much more significant (again, that is mostly the case). Setting a Maximum DOP for a Statement Now that you know how to control how many of your statements are considered to run in parallel, lets talk about the specific degree of any given statement that will be evaluated. As the initial post describes this is controlled by PARALLEL_DEGREE_LIMIT. This parameter controls the degree on the entire cluster and by default it is CPU (meaning it equals Default DOP). For the sake of an example, let’s say our Default DOP is 32. Looking at our 5 minute queries from the previous paragraph, the limit to 32 means that none of the statements that are evaluated for Auto DOP ever runs at more than DOP of 32. Concurrently Running a High DOP A basic assumption about running high DOP statements at high concurrency is that you at some point in time (and this is true on any parallel processing platform!) will run into a resource limitation. And yes, you can then buy more hardware (e.g. expand the Database Machine in Oracle’s case), but that is not the point of this post… The goal is to find a balance between the highest possible DOP for each statement and the number of statements running concurrently, but with an emphasis on running each statement at that highest efficiency DOP. The PARALLEL_SERVER_TARGET parameter is the all important concurrency slider here. Setting this parameter to a higher number means more statements get to run at their maximum parallel degree before queuing kicks in.  PARALLEL_SERVER_TARGET is set per instance (so needs to be set to the same value on all 8 nodes in a full rack Database Machine). Just as a side note, this parameter is set in processes, not in DOP, which equates to 4* Default DOP (2 processes for a DOP, default value is 2 * Default DOP, hence a default of 4 * Default DOP). Let’s say we have PARALLEL_SERVER_TARGET set to 128. With our limit set to 32 (the default) we are able to run 4 statements concurrently at the highest DOP possible on this system before we start queuing. If these 4 statements are running, any next statement will be queued. To run a system at high concurrency the PARALLEL_SERVER_TARGET should be raised from its default to be much closer (start with 60% or so) to PARALLEL_MAX_SERVERS. By using both PARALLEL_SERVER_TARGET and PARALLEL_DEGREE_LIMIT you can control easily how many statements run concurrently at good DOPs without excessive queuing. Because each workload is a little different, it makes sense to plan ahead and look at these parameters and set these based on your requirements.

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• ASP.NET WebAPI Security 2: Identity Architecture

  - by Your DisplayName here!

  Pedro has beaten me to the punch with a detailed post (and diagram) about the WebAPI hosting architecture. So go read his post first, then come back so we can have a closer look at what that means for security. The first important takeaway is that WebAPI is hosting independent-  currently it ships with two host integration implementations – one for ASP.NET (aka web host) and WCF (aka self host). Pedro nicely shows the integration into the web host. Self hosting is not done yet so we will mainly focus on the web hosting case and I will point out security related differences when they exist. The interesting part for security (amongst other things of course) is the HttpControllerHandler (see Pedro’s diagram) – this is where the host specific representation of an HTTP request gets converted to the WebAPI abstraction (called HttpRequestMessage). The ConvertRequest method does the following: Create a new HttpRequestMessage. Copy URI, method and headers from the HttpContext. Copies HttpContext.User to the Properties<string, object> dictionary on the HttpRequestMessage. The key used for that can be found on HttpPropertyKeys.UserPrincipalKey (which resolves to “MS_UserPrincipal”). So the consequence is that WebAPI receives whatever IPrincipal has been set by the ASP.NET pipeline (in the web hosting case). Common questions are: Are there situations where is property does not get set? Not in ASP.NET – the DefaultAuthenticationModule in the HTTP pipeline makes sure HttpContext.User (and Thread.CurrentPrincipal – more on that later) are always set. Either to some authenticated user – or to an anonymous principal. This may be different in other hosting environments (again more on that later). Why so generic? Keep in mind that WebAPI is hosting independent and may run on a host that materializes identity completely different compared to ASP.NET (or .NET in general). This gives them a way to evolve the system in the future. How does WebAPI code retrieve the current client identity? HttpRequestMessage has an extension method called GetUserPrincipal() which returns the property as an IPrincipal. A quick look at self hosting shows that the moral equivalent of HttpControllerHandler.ConvertRequest() is HttpSelfHostServer.ProcessRequestContext(). Here the principal property gets only set when the host is configured for Windows authentication (inconsisteny). Do I like that? Well – yes and no. Here are my thoughts: I like that it is very straightforward to let WebAPI inherit the client identity context of the host. This might not always be what you want – think of an ASP.NET app that consists of UI and APIs – the UI might use Forms authentication, the APIs token based authentication. So it would be good if the two parts would live in a separate security world. It makes total sense to have this generic hand off point for identity between the host and WebAPI. It also makes total sense for WebAPI plumbing code (especially handlers) to use the WebAPI specific identity abstraction. But – c’mon we are running on .NET. And the way .NET represents identity is via IPrincipal/IIdentity. That’s what every .NET developer on this planet is used to. So I would like to see a User property of type IPrincipal on ApiController. I don’t like the fact that Thread.CurrentPrincipal is not populated. T.CP is a well established pattern as a one stop shop to retrieve client identity on .NET.  That makes a lot of sense – even if the name is misleading at best. There might be existing library code you want to call from WebAPI that makes use of T.CP (e.g. PrincipalPermission, or a simple .Name or .IsInRole()). Having the client identity as an ambient property is useful for code that does not have access to the current HTTP request (for calling GetUserPrincipal()). I don’t like the fact that that the client identity conversion from host to WebAPI is inconsistent. This makes writing security plumbing code harder. I think the logic should always be: If the host has a client identity representation, copy it. If not, set an anonymous principal on the request message. Btw – please don’t annoy me with the “but T.CP is static, and static is bad for testing” chant. T.CP is a getter/setter and, in fact I find it beneficial to be able to set different security contexts in unit tests before calling in some logic. And, in case you have wondered – T.CP is indeed thread static (and the name comes from a time where a logical operation was bound to a thread – which is not true anymore). But all thread creation APIs in .NET actually copy T.CP to the new thread they create. This is the case since .NET 2.0 and is certainly an improvement compared to how Win32 does things. So to sum it up: The host plumbing copies the host client identity to WebAPI (this is not perfect yet, but will surely be improved). or in other words: The current WebAPI bits don’t ship with any authentication plumbing, but solely use whatever authentication (and thus client identity) is set up by the host. WebAPI developers can retrieve the client identity from the HttpRequestMessage. Hopefully my proposed changes around T.CP and the User property on ApiController will be added. In the next post, I will detail how to add WebAPI specific authentication support, e.g. for Basic Authentication and tokens. This includes integrating the notion of claims based identity. After that we will look at the built-in authorization bits and how to improve them as well. Stay tuned.

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