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  • When should I use MySQL compressed protocol?

    - by ento
    I've learned that MySQL can compress communication between servers and clients. Compression is used if both client and server support zlib compression, and the client requests compression. (from MySQL Forge Wiki) The most obvious pros and cons are pros: Reduced payload size cons: Increased computation time So, is compressed protocol something I should enable whenever I can afford servers with adequate specs? Are there other factors I should consider?

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  • Performance Cost of a Memcopy in C/C++

    - by Cenoc
    So whenever I write code I always think about the performance implications. I've often wondered, what is the "cost" of using a memcopy relative to other functions in terms of performance? For example, I may be writing a sequence of numbers to a static buffer and concentrate on a frame within the buffer, in order to keep the frame once I get to the end of the buffer, I might memcopy all of it to the beginning OR I can implement an algorithm to amortize the computation.

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  • Approaches for Content-based Item Recommendations

    - by PartlyCloudy
    Hello, I'm currently developing an application where I want to group similar items. Items (like videos) can be created by users and also their attributes can be altered or extended later (like new tags). Instead of relying on users' preferences as most collaborative filtering mechanisms do, I want to compare item similarity based on the items' attributes (like similar length, similar colors, similar set of tags, etc.). The computation is necessary for two main purposes: Suggesting x similar items for a given item and for clustering into groups of similar items. My application so far is follows an asynchronous design and I want to decouple this clustering component as far as possible. The creation of new items or the addition of new attributes for an existing item will be advertised by publishing events the component can then consume. Computations can be provided best-effort and "snapshotted", which means that I'm okay with the best result possible at a given point in time, although result quality will eventually increase. So I am now searching for appropriate algorithms to compute both similar items and clusters. At important constraint is scalability. Initially the application has to handle a few thousand items, but later million items might be possible as well. Of course, computations will then be executed on additional nodes, but the algorithm itself should scale. It would also be nice if the algorithm supports some kind of incremental mode on partial changes of the data. My initial thought of comparing each item with each other and storing the numerical similarity sounds a little bit crude. Also, it requires n*(n-1)/2 entries for storing all similarities and any change or new item will eventually cause n similarity computations. Thanks in advance! UPDATE tl;dr To clarify what I want, here is my targeted scenario: User generate entries (think of documents) User edit entry meta data (think of tags) And here is what my system should provide: List of similar entries to a given item as recommendation Clusters of similar entries Both calculations should be based on: The meta data/attributes of entries (i.e. usage of similar tags) Thus, the distance of two entries using appropriate metrics NOT based on user votings, preferences or actions (unlike collaborative filtering). Although users may create entries and change attributes, the computation should only take into account the items and their attributes, and not the users associated with (just like a system where only items and no users exist). Ideally, the algorithm should support: permanent changes of attributes of an entry incrementally compute similar entries/clusters on changes scale something better than a simple distance table, if possible (because of the O(n²) space complexity)

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  • sapply and concurrency in R

    - by JSmaga
    Good afternoon, Somebody asked me a question today and neither did I know the answer nor could I find it in the documentation. This person simply asked me if the sapply function in R was making concurrent calls to the function you want to apply to the list, or if the computation is done sequantially. Does anybody know the answer? What about rapply (the recursive version of this function)? Thanks, Jeremie

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  • C#. Where struct methods code kept in memory?

    - by maxima120
    It is somewhat known where .NET keeps value types in memory (mostly in stack but could be in heap in certain circumstances etc)... My question is - where is the code of the struct? If I have say 16 byte of data fields in the struct and a massive computation method in it - I am presuming that 16 byte will be copied in stack and the method code is stored somewhere else and is shared for all instances of the struct. Are these presumptions correct?

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  • Speeding up Math calculations in Java

    - by Simon
    I have a neural network written in Java which uses a sigmoid transfer function defined as follows: private static double sigmoid(double x) { return 1 / (1 + Math.exp(-x)); } and this is called many times during training and computation using the network. Is there any way of speeding this up? It's not that it's slow, it's just that it is used a lot, so a small optimisation here would be a big overall gain.

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  • Is nginx / node.js / postgres a very scalable architecture?

    - by Luc
    I have an app running with: one instance of nginx as the frontend (serving static file) a cluster of node.js application for the backend (using cluster and expressjs modules) one instance of Postgres as the DB Is this architecture sufficient if the application needs scalability (this is only for HTTP / REST requests) for: 500 request per seconds (each requests only fetches data from the DB, those data could be several ko, and with no big computation needed after the fetch). 20000 users connected at the same time Where could be the bottlenecks ?

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  • Project Euler considered harmful

    - by xxxxxxx
    Hi, I've done some Project Euler problems and I was able to solve them very fast because I already knew all the theory behind them. I learned that "accidentaly" because I also had to learn it for university. I used to also solve olympiad problems, I wasn't very good but I was solving some of the problems. I've reached the conclusion that Project Euler problems are taken out of their context(and olympiad problems as well). That's why they are hard. Mathematics and it's theory is taught in order to make the problems easy. However, Project Euler apparently makes an invitation at making them hard again. Why ? I honestly think this is a complete waste of time. Mathematicians had centuries at their disposal in order to solve math problems and they developed theories to explain properly why certain things happen. I think olympiad problems and Project Euler problems are really useless. What's your take on Project Euler ? Do you get something out of it or do you just find formulas on some websites and implement the code fast and then get the result and solve the problem ?

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  • BITS client fails to specify HTTP Range header

    - by user256890
    Our system is designed to deploy to regions with unreliable and/or insufficient network connections. We build our own fault tolerating data replication services that uses BITS. Due to some security and maintenance requirements, we implemented our own ASP.NET file download service on the server side, instead of just letting IIS serving up the files. When BITS client makes an HTTP download request with the specified range of the file, our ASP.NET page pulls the demanded file segment into memory and serve that up as the HTTP response. That is the theory. ;) This theory fails in artificial lab scenarios but I would not let the system deploy in real life scenarios unless we can overcome that. Lab scenario: I have BITS client and the IIS on the same developer machine, so practically I have enormous network "bandwidth" and BITS is intelligent enough to detect that. As BITS client discovers the unlimited bandwidth, it gets more and more "greedy". At each HTTP request, BITS wants to grasp greater and greater file ranges (we are talking about downloading CD iso files, videos), demanding 20-40MB inside a single HTTP request, a size that I am not comfortable to pull into memory on the server side as one go. I can overcome that simply by giving less than demanded. It is OK. However, BITS gets really "confident" and "arrogant" demanding files WITHOUT specifying the download range, i.e., it wants the entire file in a single request, and this is where things go wrong. I do not know how to answer that response in the case of a 600MB file. If I just provide the starting 1MB range of the file, BITS client keeps sending HTTP requests for the same file without download range to continue, it hammers its point that it wants the entire file in one go. Since I am reluctant to provide the entire file, BITS gives up after several trials and reports error. Any thoughts?

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  • how to export bind and keyframe bone poses from blender to use in OpenGL

    - by SaldaVonSchwartz
    EDIT: I decided to reformulate the question in much simpler terms to see if someone can give me a hand with this. Basically, I'm exporting meshes, skeletons and actions from blender into an engine of sorts that I'm working on. But I'm getting the animations wrong. I can tell the basic motion paths are being followed but there's always an axis of translation or rotation which is wrong. I think the problem is most likely not in my engine code (OpenGL-based) but rather in either my misunderstanding of some part of the theory behind skeletal animation / skinning or the way I am exporting the appropriate joint matrices from blender in my exporter script. I'll explain the theory, the engine animation system and my blender export script, hoping someone might catch the error in either or all of these. The theory: (I'm using column-major ordering since that's what I use in the engine cause it's OpenGL-based) Assume I have a mesh made up of a single vertex v, along with a transformation matrix M which takes the vertex v from the mesh's local space to world space. That is, if I was to render the mesh without a skeleton, the final position would be gl_Position = ProjectionMatrix * M * v. Now assume I have a skeleton with a single joint j in bind / rest pose. j is actually another matrix. A transform from j's local space to its parent space which I'll denote Bj. if j was part of a joint hierarchy in the skeleton, Bj would take from j space to j-1 space (that is to its parent space). However, in this example j is the only joint, so Bj takes from j space to world space, like M does for v. Now further assume I have a a set of frames, each with a second transform Cj, which works the same as Bj only that for a different, arbitrary spatial configuration of join j. Cj still takes vertices from j space to world space but j is rotated and/or translated and/or scaled. Given the above, in order to skin vertex v at keyframe n. I need to: take v from world space to joint j space modify j (while v stays fixed in j space and is thus taken along in the transformation) take v back from the modified j space to world space So the mathematical implementation of the above would be: v' = Cj * Bj^-1 * v. Actually, I have one doubt here.. I said the mesh to which v belongs has a transform M which takes from model space to world space. And I've also read in a couple textbooks that it needs to be transformed from model space to joint space. But I also said in 1 that v needs to be transformed from world to joint space. So basically I'm not sure if I need to do v' = Cj * Bj^-1 * v or v' = Cj * Bj^-1 * M * v. Right now my implementation multiples v' by M and not v. But I've tried changing this and it just screws things up in a different way cause there's something else wrong. Finally, If we wanted to skin a vertex to a joint j1 which in turn is a child of a joint j0, Bj1 would be Bj0 * Bj1 and Cj1 would be Cj0 * Cj1. But Since skinning is defined as v' = Cj * Bj^-1 * v , Bj1^-1 would be the reverse concatenation of the inverses making up the original product. That is, v' = Cj0 * Cj1 * Bj1^-1 * Bj0^-1 * v Now on to the implementation (Blender side): Assume the following mesh made up of 1 cube, whose vertices are bound to a single joint in a single-joint skeleton: Assume also there's a 60-frame, 3-keyframe animation at 60 fps. The animation essentially is: keyframe 0: the joint is in bind / rest pose (the way you see it in the image). keyframe 30: the joint translates up (+z in blender) some amount and at the same time rotates pi/4 rad clockwise. keyframe 59: the joint goes back to the same configuration it was in keyframe 0. My first source of confusion on the blender side is its coordinate system (as opposed to OpenGL's default) and the different matrices accessible through the python api. Right now, this is what my export script does about translating blender's coordinate system to OpenGL's standard system: # World transform: Blender -> OpenGL worldTransform = Matrix().Identity(4) worldTransform *= Matrix.Scale(-1, 4, (0,0,1)) worldTransform *= Matrix.Rotation(radians(90), 4, "X") # Mesh (local) transform matrix file.write('Mesh Transform:\n') localTransform = mesh.matrix_local.copy() localTransform = worldTransform * localTransform for col in localTransform.col: file.write('{:9f} {:9f} {:9f} {:9f}\n'.format(col[0], col[1], col[2], col[3])) file.write('\n') So if you will, my "world" matrix is basically the act of changing blenders coordinate system to the default GL one with +y up, +x right and -z into the viewing volume. Then I also premultiply (in the sense that it's done by the time we reach the engine, not in the sense of post or pre in terms of matrix multiplication order) the mesh matrix M so that I don't need to multiply it again once per draw call in the engine. About the possible matrices to extract from Blender joints (bones in Blender parlance), I'm doing the following: For joint bind poses: def DFSJointTraversal(file, skeleton, jointList): for joint in jointList: bindPoseJoint = skeleton.data.bones[joint.name] bindPoseTransform = bindPoseJoint.matrix_local.inverted() file.write('Joint ' + joint.name + ' Transform {\n') translationV = bindPoseTransform.to_translation() rotationQ = bindPoseTransform.to_3x3().to_quaternion() scaleV = bindPoseTransform.to_scale() file.write('T {:9f} {:9f} {:9f}\n'.format(translationV[0], translationV[1], translationV[2])) file.write('Q {:9f} {:9f} {:9f} {:9f}\n'.format(rotationQ[1], rotationQ[2], rotationQ[3], rotationQ[0])) file.write('S {:9f} {:9f} {:9f}\n'.format(scaleV[0], scaleV[1], scaleV[2])) DFSJointTraversal(file, skeleton, joint.children) file.write('}\n') Note that I'm actually grabbing the inverse of what I think is the bind pose transform Bj. This is so I don't need to invert it in the engine. Also note I went for matrix_local, assuming this is Bj. The other option is plain "matrix", which as far as I can tell is the same only that not homogeneous. For joint current / keyframe poses: for kfIndex in keyframes: bpy.context.scene.frame_set(kfIndex) file.write('keyframe: {:d}\n'.format(int(kfIndex))) for i in range(0, len(skeleton.data.bones)): file.write('joint: {:d}\n'.format(i)) currentPoseJoint = skeleton.pose.bones[i] currentPoseTransform = currentPoseJoint.matrix translationV = currentPoseTransform.to_translation() rotationQ = currentPoseTransform.to_3x3().to_quaternion() scaleV = currentPoseTransform.to_scale() file.write('T {:9f} {:9f} {:9f}\n'.format(translationV[0], translationV[1], translationV[2])) file.write('Q {:9f} {:9f} {:9f} {:9f}\n'.format(rotationQ[1], rotationQ[2], rotationQ[3], rotationQ[0])) file.write('S {:9f} {:9f} {:9f}\n'.format(scaleV[0], scaleV[1], scaleV[2])) file.write('\n') Note that here I go for skeleton.pose.bones instead of data.bones and that I have a choice of 3 matrices: matrix, matrix_basis and matrix_channel. From the descriptions in the python API docs I'm not super clear which one I should choose, though I think it's the plain matrix. Also note I do not invert the matrix in this case. The implementation (Engine / OpenGL side): My animation subsystem does the following on each update (I'm omitting parts of the update loop where it's figured out which objects need update and time is hardcoded here for simplicity): static double time = 0; time = fmod((time + elapsedTime),1.); uint16_t LERPKeyframeNumber = 60 * time; uint16_t lkeyframeNumber = 0; uint16_t lkeyframeIndex = 0; uint16_t rkeyframeNumber = 0; uint16_t rkeyframeIndex = 0; for (int i = 0; i < aClip.keyframesCount; i++) { uint16_t keyframeNumber = aClip.keyframes[i].number; if (keyframeNumber <= LERPKeyframeNumber) { lkeyframeIndex = i; lkeyframeNumber = keyframeNumber; } else { rkeyframeIndex = i; rkeyframeNumber = keyframeNumber; break; } } double lTime = lkeyframeNumber / 60.; double rTime = rkeyframeNumber / 60.; double blendFactor = (time - lTime) / (rTime - lTime); GLKMatrix4 bindPosePalette[aSkeleton.jointsCount]; GLKMatrix4 currentPosePalette[aSkeleton.jointsCount]; for (int i = 0; i < aSkeleton.jointsCount; i++) { F3DETQSType& lPose = aClip.keyframes[lkeyframeIndex].skeletonPose.joints[i]; F3DETQSType& rPose = aClip.keyframes[rkeyframeIndex].skeletonPose.joints[i]; GLKVector3 LERPTranslation = GLKVector3Lerp(lPose.t, rPose.t, blendFactor); GLKQuaternion SLERPRotation = GLKQuaternionSlerp(lPose.q, rPose.q, blendFactor); GLKVector3 LERPScaling = GLKVector3Lerp(lPose.s, rPose.s, blendFactor); GLKMatrix4 currentTransform = GLKMatrix4MakeWithQuaternion(SLERPRotation); currentTransform = GLKMatrix4TranslateWithVector3(currentTransform, LERPTranslation); currentTransform = GLKMatrix4ScaleWithVector3(currentTransform, LERPScaling); GLKMatrix4 inverseBindTransform = GLKMatrix4MakeWithQuaternion(aSkeleton.joints[i].inverseBindTransform.q); inverseBindTransform = GLKMatrix4TranslateWithVector3(inverseBindTransform, aSkeleton.joints[i].inverseBindTransform.t); inverseBindTransform = GLKMatrix4ScaleWithVector3(inverseBindTransform, aSkeleton.joints[i].inverseBindTransform.s); if (aSkeleton.joints[i].parentIndex == -1) { bindPosePalette[i] = inverseBindTransform; currentPosePalette[i] = currentTransform; } else { bindPosePalette[i] = GLKMatrix4Multiply(inverseBindTransform, bindPosePalette[aSkeleton.joints[i].parentIndex]); currentPosePalette[i] = GLKMatrix4Multiply(currentPosePalette[aSkeleton.joints[i].parentIndex], currentTransform); } aSkeleton.skinningPalette[i] = GLKMatrix4Multiply(currentPosePalette[i], bindPosePalette[i]); } Finally, this is my vertex shader: #version 100 uniform mat4 modelMatrix; uniform mat3 normalMatrix; uniform mat4 projectionMatrix; uniform mat4 skinningPalette[6]; uniform lowp float skinningEnabled; attribute vec4 position; attribute vec3 normal; attribute vec2 tCoordinates; attribute vec4 jointsWeights; attribute vec4 jointsIndices; varying highp vec2 tCoordinatesVarying; varying highp float lIntensity; void main() { tCoordinatesVarying = tCoordinates; vec4 skinnedVertexPosition = vec4(0.); for (int i = 0; i < 4; i++) { skinnedVertexPosition += jointsWeights[i] * skinningPalette[int(jointsIndices[i])] * position; } vec4 skinnedNormal = vec4(0.); for (int i = 0; i < 4; i++) { skinnedNormal += jointsWeights[i] * skinningPalette[int(jointsIndices[i])] * vec4(normal, 0.); } vec4 finalPosition = mix(position, skinnedVertexPosition, skinningEnabled); vec4 finalNormal = mix(vec4(normal, 0.), skinnedNormal, skinningEnabled); vec3 eyeNormal = normalize(normalMatrix * finalNormal.xyz); vec3 lightPosition = vec3(0., 0., 2.); lIntensity = max(0.0, dot(eyeNormal, normalize(lightPosition))); gl_Position = projectionMatrix * modelMatrix * finalPosition; } The result is that the animation displays wrong in terms of orientation. That is, instead of bobbing up and down it bobs in and out (along what I think is the Z axis according to my transform in the export clip). And the rotation angle is counterclockwise instead of clockwise. If I try with a more than one joint, then it's almost as if the second joint rotates in it's own different coordinate space and does not follow 100% its parent's transform. Which I assume it should from my animation subsystem which I assume in turn follows the theory I explained for the case of more than one joint. Any thoughts?

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  • What are the most interesting equivalences arising from the Curry-Howard Isomorphism?

    - by Tom
    I came upon the Curry-Howard Isomorphism relatively late in my programming life, and perhaps this contributes to my being utterly fascinated by it. It implies that for every programming concept there exists a precise analogue in formal logic, and vice versa. Here's an "obvious" list of such analogies, off the top of my head: program/definition | proof type/declaration | proposition inhabited type | theorem function | implication function argument | hypothesis/antecedent function result | conclusion/consequent function application | modus ponens recursion | induction identity function | tautology non-terminating function | absurdity tuple | conjunction (and) disjoint union | exclusive disjunction (xor) parametric polymorphism | universal quantification So, to my question: what are some of the more interesting/obscure implications of this isomorphism? I'm no logician so I'm sure I've only scratched the surface with this list. For example, here are some programming notions for which I'm unaware of pithy names in logic: currying | "((a & b) => c) iff (a => (b => c))" scope | "known theory + hypotheses" And here are some logical concepts which I haven't quite pinned down in programming terms: primitive type? | axiom set of valid programs? | theory ? | disjunction (or)

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  • Easy way to lock a file on a remote machine (windows)?

    - by roufamatic
    I've tracked down an error in my logs, and am trying to reproduce it. My theory is that a file sometimes gets locked in a specific folder, and when the application (ASP.NET) tries to delete that folder it hangs. I don't have the application running on my own machine so I'm debugging this on a remote server. But for the life of me, I can't seem to figure out a way to lock a file that prevents it from being deleted by the process. My first thought was to map the network path to a local drive and just leave a command prompt open to that folder. Locally that always fouls up my folder deletes, but apparently SMB is a bit more robust and doesn't grant me a lock. After that I created an infinte loop vbscript in the folder and executed it remotely. The file was deleted out from underneath the executing code. Man! I then tried creating a file on the server in that folder and removing all permissions. That didn't do the trick. I don't have access to the IIS settings so perhaps it's running under a privileged system account. So: what's a program that you know is free and I can quickly use to create an exclusive lock on a file so I can test my delete theory? Like a really, really bad Notepad clone or something. :-)

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  • Pecking order of pigeons?

    - by sc_ray
    I was going though problems on graph theory posted by Prof. Ericksson from my alma-mater and came across this rather unique question about pigeons and their innate tendency to form pecking orders. The question goes as follows: Whenever groups of pigeons gather, they instinctively establish a pecking order. For any pair of pigeons, one pigeon always pecks the other, driving it away from food or potential mates. The same pair of pigeons always chooses the same pecking order, even after years of separation, no matter what other pigeons are around. Surprisingly, the overall pecking order can contain cycles—for example, pigeon A pecks pigeon B, which pecks pigeon C, which pecks pigeon A. Prove that any finite set of pigeons can be arranged in a row from left to right so that every pigeon pecks the pigeon immediately to its left. Since this is a question on Graph theory, the first things that crossed my mind that is this just asking for a topological sort of a graphs of relationships(relationships being the pecking order). What made this a little more complex was the fact that there can be cyclic relationships between the pigeons. If we have a cyclic dependency as follows: A-B-C-A where A pecks on B,B pecks on C and C goes back and pecks on A If we represent it in the way suggested by the problem, we have something as follows: C B A But the above given row ordering does not factor in the pecking order between C and A. I had another idea of solving it by mathematical induction where the base case is for two pigeons arranged according to their pecking order, assuming the pecking order arrangement is valid for n pigeons and then proving it to be true for n+1 pigeons. I am not sure if I am going down the wrong track here. Some insights into how I should be analyzing this problem will be helpful. Thanks

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  • Effective books for learning the intricacies of business application development?

    - by OffApps Cory
    I am a self taught "developer". I use the term loosely because I only know enough to make myself dangerous. I have no theory background, and I only pick up things to get this little tool to work or make that control do what I want. That said, I am looking for some reading material that explains some of the theory behind application development especially from a business standpoint. Really I need to understand what all of these terms that float around really talk about. Business Logic Layer, UI abstraction level and all that. Anyone got a reading list that they feel helped them understand this stuff? I know how to code stuff up so that it works. It is not pretty mostly because I don't know the elegant way of doing it, and it is not planned out very well (I also don't know how to plan an application). Any help would be appreciated. I have read a number of books on what I thought was the subject, but they all seem to rehash basic coding and what-not. This doesn't have to be specific to VB.NET or WPF (or Entity Framework) but anything with those items would be quite helpful.

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  • Spring MVC: How to get the remaining path after the controller path?

    - by Willis Blackburn
    I've spent over an hour trying to find the answer to this question, which seems like it should reflect a common use case, but I can't figure it out! Basically I am writing a file-serving controller using Spring MVC. The URLs are of the format http://www.bighost.com/serve/the/path/to/the/file.jpg, in which the part after "/serve" is the path to the requested file, which may have an arbitrary number of path segments. I have a controller like this: @Controller class ServerController { @RequestMapping(value = "/serve/???") public void serve(???) { } } What I am trying to figure out is: What do I use in place of "???" to make this work? I have two theories about how this should work. The first theory is that I could replace the first "???" in the RequestMapping with a path variable placeholder that has some special syntax meaning "capture to the end of the path." If a regular placeholder looks like "{path}" then maybe I could use "{path:**}" or "{path:/}" or something like that. Then I could use a @PathVariable annotation to refer to the path variable in the second "???". The other theory is that I could replace the first "???" with "**" (match anything) and that Spring would give me an API to obtain the remainder of the path (the part matching the "**"). But I can't find such an API. Thanks for any help you can provide!

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  • How do i set the Transaction Isolation in EJB?

    - by Nitesh Panchal
    Hello, I am not able to find a way to set TransactionIsolation in ejb. Can anybody tell me how do i set it? I am using persistence. I have looked the following classes : EntityManager , EntityManagerFactory, UserTransaction. None of them seems to have any method like setTransactionIsolation or such. Do we need to change persistence.xml? I just read a book named Mastering EJB 3.0 4th edition. They gave a full 10 page theory about Isolation level that this problems occur and that occurs and such things but at the end they gave this paragraph :- "As we now know, the EJB standard does not deal with isolation levels directly, and rightly so. EJB is a component specification. It defines the behavior and contracts of a business component with clients and middleware infrastructure (containers) such that the component can be rendered as various middleware services properly. EJBs therefore are transactional components that interact with resource managers, such as the JDBC resource manager or JMS resource manager, via JTS, as part of a transaction. They are not, hence, resource components in themselves. Since isolation levels are very specific to the behavior and capabilities of the underlying resources, they should therefore be specified at the resource API levels. " What exactly does it mean? What is meant by resource level APIs? Please help me. If persistence has no way to set Isolation Level then why do they give such huge theory in an EJB book and make it heavy in weight unnecessarily :(

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  • Callbacks on GUI Thread

    - by miguel
    We have an external data provider which, in its construtor, takes a callback thread for returning data upon. There are some issues in the system which I am suspicious are related to threading, however, in theory they cannot be, due to the fact that the callbacks should all be returned on the same thread. My question is, does code like this require thread synchronisation? class Foo { ExternalDataProvider _provider; public Foo() { // This is the c'tor for the xternal data provider, taking a callback loop as param _provider = new ExternalDataProvider(UILoop); _provider.DataArrived += ExternalProviderCallbackMethod; } public ExternalProviderCallbackMethod() { var itemArray[] = new String[4] { "item1", "item2", "item3", "item4" }; for (int i = 0; i < itemArray.Length; i++) { string s = itemArray[i]; switch(s) { case "item1": DoItem1Action(); break; case "item2": DoItem2Action(); break; default: DoDefaultAction(); break; } } } } The issue is that, very infrequently, DoItem2Action is executingwhen DoItem1Action should be exectuing. Is it at all possible threading is at fault here? In theory, as all callbacks are arriving on the same thread, they should be serialized, right? So there should be no need for thread sync here?

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  • All Callbacks on GUI Thread - Multithreading issues possible?

    - by miguel
    We have an external data provider which, in its construtor, takes a callback thread for returning data upon. There are some issues in the system which I am suspicious are related to threading, however, in theory they cannot be, due to the fact that the callbacks should all be returned on the same thread. My question is, does code like this require thread synchronisation? class Foo { ExternalDataProvider _provider; public Foo() { // This is the c'tor for the xternal data provider, taking a callback loop as param _provider = new ExternalDataProvider(UILoop); _provider.DataArrived += ExternalProviderCallbackMethod; } public ExternalProviderCallbackMethod(...) { //...(code omitted) var itemArray[] = new String[4] { "item1", "item2", "item3", "item4" }; for (int i = 0; i < itemArray.Length; i++) { string s = itemArray[i]; switch(s) { case "item1": DoItem1Action(); break; case "item2": DoItem2Action(); break; default: DoDefaultAction(); break; } //...(code omitted) } } } The issue is that, very infrequently, DoItem2Action is executingwhen DoItem1Action should be exectuing. Is it at all possible threading is at fault here? In theory, as all callbacks are arriving on the same thread, they should be serialized, right? So there should be no need for thread sync here?

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  • Criteria for triggering garbage collection in .Net

    - by Kennet Belenky
    I've come across some curious behavior with regard to garbage collection in .Net. The following program will throw an OutOfMemoryException very quickly (after less than a second on a 32-bit, 2GB machine). The Foo finalizer is never called. class Foo { static Dictionary<Guid, WeakReference> allFoos = new Dictionary<Guid, WeakReference>(); Guid guid = Guid.NewGuid(); byte[] buffer = new byte[1000000]; static Random rand = new Random(); public Foo() { // Uncomment the following line and the program will run forever. // rand.NextBytes(buffer); allFoos[guid] = new WeakReference(this); } ~Foo() { allFoos.Remove(guid); } static public void Main(string args[]) { for (; ; ) { new Foo(); } } } If the rand.nextBytes line is uncommented, it will run ad infinitum, and the Foo finalizer is regularly invoked. Why is that? My best guess is that in the former case, either the CLR or the Windows VMM is lazy about allocating physical memory. The buffer never gets written to, so the physical memory is never used. When the address space runs out, the system crashes. In the latter case, the system runs out of physical memory before it runs out of address space, the GC is triggered and the objects are collected. However, here's the part I don't get. Assuming my theory is correct, why doesn't the GC trigger when the address space runs low? If my theory is incorrect, then what's the real explanation?

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  • EM12c Release 4: New EMCLI Verbs

    - by SubinDaniVarughese
    Here are the new EM CLI verbs in Enterprise Manager 12c Release 4 (12.1.0.4). This helps you in writing new scripts or enhancing your existing scripts for further automation. Basic Administration Verbs invoke_ws - Invoke EM web service.ADM Verbs associate_target_to_adm - Associate a target to an application data model. export_adm - Export Application Data Model to a specified .xml file. import_adm - Import Application Data Model from a specified .xml file. list_adms - List the names, target names and application suites of existing Application Data Models verify_adm - Submit an application data model verify job for the target specified.Agent Update Verbs get_agent_update_status -  Show Agent Update Results get_not_updatable_agents - Shows Not Updatable Agents get_updatable_agents - Show Updatable Agents update_agents - Performs Agent Update Prereqs and submits Agent Update JobBI Publisher Reports Verbs grant_bipublisher_roles - Grants access to the BI Publisher catalog and features. revoke_bipublisher_roles - Revokes access to the BI Publisher catalog and features.Blackout Verbs create_rbk - Create a Retro-active blackout.CFW Verbs cancel_cloud_service_requests -  To cancel cloud service requests delete_cloud_service_instances -  To delete cloud service instances delete_cloud_user_objects - To delete cloud user objects. get_cloud_service_instances - To get information about cloud service instances get_cloud_service_requests - To get information about cloud requests get_cloud_user_objects - To get information about cloud user objects.Chargeback Verbs add_chargeback_entity - Adds the given entity to Chargeback. assign_charge_plan - Assign a plan to a chargeback entity. assign_cost_center - Assign a cost center to a chargeback entity. create_charge_entity_type - Create  charge entity type export_charge_plans - Exports charge plans metadata to file export_custom_charge_items -  Exports user defined charge items to a file import_charge_plans - Imports charge plans metadata from given file import_custom_charge_items -  Imports user defined charge items metadata from given file list_charge_plans - Gives a list of charge plans in Chargeback. list_chargeback_entities - Gives a list of all the entities in Chargeback list_chargeback_entity_types - Gives a list of all the entity types that are supported in Chargeback list_cost_centers - Lists the cost centers in Chargeback. remove_chargeback_entity - Removes the given entity from Chargeback. unassign_charge_plan - Un-assign the plan associated to a chargeback entity. unassign_cost_center - Un-assign the cost center associated to a chargeback entity.Configuration/Association History disable_config_history - Disable configuration history computation for a target type. enable_config_history - Enable configuration history computation for a target type. set_config_history_retention_period - Sets the amount of time for which Configuration History is retained.ConfigurationCompare config_compare - Submits the configuration comparison job get_config_templates - Gets all the comparison templates from the repositoryCompliance Verbs fix_compliance_state -  Fix compliance state by removing references in deleted targets.Credential Verbs update_credential_setData Subset Verbs export_subset_definition - Exports specified subset definition as XML file at specified directory path. generate_subset - Generate subset using specified subset definition and target database. import_subset_definition - Import a subset definition from specified XML file. import_subset_dump - Imports dump file into specified target database. list_subset_definitions - Get the list of subset definition, adm and target nameDelete pluggable Database Job Verbs delete_pluggable_database - Delete a pluggable databaseDeployment Procedure Verbs get_runtime_data - Get the runtime data of an executionDiscover and Push to Agents Verbs generate_discovery_input - Generate Discovery Input file for discovering Auto-Discovered Domains refresh_fa - Refresh Fusion Instance run_fa_diagnostics - Run Fusion Applications DiagnosticsFusion Middleware Provisioning Verbs create_fmw_domain_profile - Create a Fusion Middleware Provisioning Profile from a WebLogic Domain create_fmw_home_profile - Create a Fusion Middleware Provisioning Profile from an Oracle Home create_inst_media_profile - Create a Fusion Middleware Provisioning Profile from Installation MediaGold Agent Image Verbs create_gold_agent_image - Creates a gold agent image. decouple_gold_agent_image - Decouples the agent from gold agent image. delete_gold_agent_image - Deletes a gold agent image. get_gold_agent_image_activity_status -  Gets gold agent image activity status. get_gold_agent_image_details - Get the gold agent image details. list_agents_on_gold_image - Lists agents on a gold agent image. list_gold_agent_image_activities - Lists gold agent image activities. list_gold_agent_image_series - Lists gold agent image series. list_gold_agent_images - Lists the available gold agent images. promote_gold_agent_image - Promotes a gold agent image. stage_gold_agent_image - Stages a gold agent image.Incident Rules Verbs add_target_to_rule_set - Add a target to an enterprise rule set. delete_incident_record - Delete one or more open incidents remove_target_from_rule_set - Remove a target from an enterprise rule set. Job Verbs export_jobs - Export job details in to an xml file import_jobs - Import job definitions from an xml file job_input_file - Supply details for a job verb in a property file resume_job - Resume a job or set of jobs suspend_job - Suspend a job or set of jobs Oracle Database as Service Verbs config_db_service_target - Configure DB Service target for OPCPrivilege Delegation Settings Verbs clear_default_privilege_delegation_setting - Clears the default privilege delegation setting for a given list of platforms set_default_privilege_delegation_setting - Sets the default privilege delegation setting for a given list of platforms test_privilege_delegation_setting - Tests a Privilege Delegation Setting on a hostSSA Verbs cleanup_dbaas_requests - Submit cleanup request for failed request create_dbaas_quota - Create Database Quota for a SSA User Role create_service_template - Create a Service Template delete_dbaas_quota - Delete the Database Quota setup for a SSA User Role delete_service_template - Delete a given service template get_dbaas_quota - List the Database Quota setup for all SSA User Roles get_dbaas_request_settings - List the Database Request Settings get_service_template_detail - Get details of a given service template get_service_templates -  Get the list of available service templates rename_service_template -  Rename a given service template update_dbaas_quota - Update the Database Quota for a SSA User Role update_dbaas_request_settings - Update the Database Request Settings update_service_template -  Update a given service template. SavedConfigurations get_saved_configs  - Gets the saved configurations from the repository Server Generated Alert Metric Verbs validate_server_generated_alerts  - Server Generated Alert Metric VerbServices Verbs edit_sl_rule - Edit the service level rule for the specified serviceSiebel Verbs list_siebel_enterprises -  List Siebel enterprises currently monitored in EM list_siebel_servers -  List Siebel servers under a specified siebel enterprise update_siebel- Update a Siebel enterprise or its underlying serversSiteGuard Verbs add_siteguard_aux_hosts -  Associate new auxiliary hosts to the system configure_siteguard_lag -  Configure apply lag and transport lag limit for databases delete_siteguard_aux_host -  Delete auxiliary host associated with a site delete_siteguard_lag -  Erases apply lag or transport lag limit for databases get_siteguard_aux_hosts -  Get all auxiliary hosts associated with a site get_siteguard_health_checks -  Shows schedule of health checks get_siteguard_lag -  Shows apply lag or transport lag limit for databases schedule_siteguard_health_checks -  Schedule health checks for an operation plan stop_siteguard_health_checks -  Stops all future health check execution of an operation plan update_siteguard_lag -  Updates apply lag and transport lag limit for databasesSoftware Library Verbs stage_swlib_entity_files -  Stage files of an entity from Software Library to a host target.Target Data Verbs create_assoc - Creates target associations delete_assoc - Deletes target associations list_allowed_pairs - Lists allowed association types for specified source and destination list_assoc - Lists associations between source and destination targets manage_agent_partnership - Manages partnership between agents. Used for explicitly assigning agent partnershipsTrace Reports generate_ui_trace_report  -  Generate and download UI Page performance report (to identify slow rendering pages)VI EMCLI Verbs add_virtual_platform - Add Oracle Virtual PLatform(s). modify_virtual_platform - Modify Oracle Virtual Platform.To get more details about each verb, execute$ emcli help <verb_name>Example: $ emcli help list_assocNew resources in list verbThese are the new resources in EM CLI list verb :Certificates  WLSCertificateDetails Credential Resource Group  PreferredCredentialsDefaultSystemScope - Preferred credentials (System Scope)   PreferredCredentialsSystemScope - Target preferred credentialPrivilege Delegation Settings  TargetPrivilegeDelegationSettingDetails  - List privilege delegation setting details on a host  TargetPrivilegeDelegationSetting - List privilege delegation settings on a host   PrivilegeDelegationSettings  - Lists all Privilege Delegation Settings   PrivilegeDelegationSettingDetails - Lists details of  Privilege Delegation Settings To get more details about each resource, execute$ emcli list -resource="<resource_name>" -helpExample: $ emcli list -resource="PrivilegeDelegationSettings" -helpDeprecated Verbs:Agent Administration Verbs resecure_agent - Resecure an agentTo get the complete list of verbs, execute:$ emcli help Stay Connected: Twitter | Facebook | YouTube | Linkedin | Newsletter Download the Oracle Enterprise Manager 12c Mobile app

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  • MapReduce in DryadLINQ and PLINQ

    - by JoshReuben
    MapReduce See http://en.wikipedia.org/wiki/Mapreduce The MapReduce pattern aims to handle large-scale computations across a cluster of servers, often involving massive amounts of data. "The computation takes a set of input key/value pairs, and produces a set of output key/value pairs. The developer expresses the computation as two Func delegates: Map and Reduce. Map - takes a single input pair and produces a set of intermediate key/value pairs. The MapReduce function groups results by key and passes them to the Reduce function. Reduce - accepts an intermediate key I and a set of values for that key. It merges together these values to form a possibly smaller set of values. Typically just zero or one output value is produced per Reduce invocation. The intermediate values are supplied to the user's Reduce function via an iterator." the canonical MapReduce example: counting word frequency in a text file.     MapReduce using DryadLINQ see http://research.microsoft.com/en-us/projects/dryadlinq/ and http://connect.microsoft.com/Dryad DryadLINQ provides a simple and straightforward way to implement MapReduce operations. This The implementation has two primary components: A Pair structure, which serves as a data container. A MapReduce method, which counts word frequency and returns the top five words. The Pair Structure - Pair has two properties: Word is a string that holds a word or key. Count is an int that holds the word count. The structure also overrides ToString to simplify printing the results. The following example shows the Pair implementation. public struct Pair { private string word; private int count; public Pair(string w, int c) { word = w; count = c; } public int Count { get { return count; } } public string Word { get { return word; } } public override string ToString() { return word + ":" + count.ToString(); } } The MapReduce function  that gets the results. the input data could be partitioned and distributed across the cluster. 1. Creates a DryadTable<LineRecord> object, inputTable, to represent the lines of input text. For partitioned data, use GetPartitionedTable<T> instead of GetTable<T> and pass the method a metadata file. 2. Applies the SelectMany operator to inputTable to transform the collection of lines into collection of words. The String.Split method converts the line into a collection of words. SelectMany concatenates the collections created by Split into a single IQueryable<string> collection named words, which represents all the words in the file. 3. Performs the Map part of the operation by applying GroupBy to the words object. The GroupBy operation groups elements with the same key, which is defined by the selector delegate. This creates a higher order collection, whose elements are groups. In this case, the delegate is an identity function, so the key is the word itself and the operation creates a groups collection that consists of groups of identical words. 4. Performs the Reduce part of the operation by applying Select to groups. This operation reduces the groups of words from Step 3 to an IQueryable<Pair> collection named counts that represents the unique words in the file and how many instances there are of each word. Each key value in groups represents a unique word, so Select creates one Pair object for each unique word. IGrouping.Count returns the number of items in the group, so each Pair object's Count member is set to the number of instances of the word. 5. Applies OrderByDescending to counts. This operation sorts the input collection in descending order of frequency and creates an ordered collection named ordered. 6. Applies Take to ordered to create an IQueryable<Pair> collection named top, which contains the 100 most common words in the input file, and their frequency. Test then uses the Pair object's ToString implementation to print the top one hundred words, and their frequency.   public static IQueryable<Pair> MapReduce( string directory, string fileName, int k) { DryadDataContext ddc = new DryadDataContext("file://" + directory); DryadTable<LineRecord> inputTable = ddc.GetTable<LineRecord>(fileName); IQueryable<string> words = inputTable.SelectMany(x => x.line.Split(' ')); IQueryable<IGrouping<string, string>> groups = words.GroupBy(x => x); IQueryable<Pair> counts = groups.Select(x => new Pair(x.Key, x.Count())); IQueryable<Pair> ordered = counts.OrderByDescending(x => x.Count); IQueryable<Pair> top = ordered.Take(k);   return top; }   To Test: IQueryable<Pair> results = MapReduce(@"c:\DryadData\input", "TestFile.txt", 100); foreach (Pair words in results) Debug.Print(words.ToString());   Note: DryadLINQ applications can use a more compact way to represent the query: return inputTable         .SelectMany(x => x.line.Split(' '))         .GroupBy(x => x)         .Select(x => new Pair(x.Key, x.Count()))         .OrderByDescending(x => x.Count)         .Take(k);     MapReduce using PLINQ The pattern is relevant even for a single multi-core machine, however. We can write our own PLINQ MapReduce in a few lines. the Map function takes a single input value and returns a set of mapped values àLINQ's SelectMany operator. These are then grouped according to an intermediate key à LINQ GroupBy operator. The Reduce function takes each intermediate key and a set of values for that key, and produces any number of outputs per key à LINQ SelectMany again. We can put all of this together to implement MapReduce in PLINQ that returns a ParallelQuery<T> public static ParallelQuery<TResult> MapReduce<TSource, TMapped, TKey, TResult>( this ParallelQuery<TSource> source, Func<TSource, IEnumerable<TMapped>> map, Func<TMapped, TKey> keySelector, Func<IGrouping<TKey, TMapped>, IEnumerable<TResult>> reduce) { return source .SelectMany(map) .GroupBy(keySelector) .SelectMany(reduce); } the map function takes in an input document and outputs all of the words in that document. The grouping phase groups all of the identical words together, such that the reduce phase can then count the words in each group and output a word/count pair for each grouping: var files = Directory.EnumerateFiles(dirPath, "*.txt").AsParallel(); var counts = files.MapReduce( path => File.ReadLines(path).SelectMany(line => line.Split(delimiters)), word => word, group => new[] { new KeyValuePair<string, int>(group.Key, group.Count()) });

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  • We've completed the first iteration

    - by CliveT
    There are a lot of features in C# that are implemented by the compiler and not by the underlying platform. One such feature is a lambda expression. Since local variables cannot be accessed once the current method activation finishes, the compiler has to go out of its way to generate a new class which acts as a home for any variable whose lifetime needs to be extended past the activation of the procedure. Take the following example:     Random generator = new Random();     Func func = () = generator.Next(10); In this case, the compiler generates a new class called c_DisplayClass1 which is marked with the CompilerGenerated attribute. [CompilerGenerated] private sealed class c__DisplayClass1 {     // Fields     public Random generator;     // Methods     public int b__0()     {         return this.generator.Next(10);     } } Two quick comments on this: (i)    A display was the means that compilers for languages like Algol recorded the various lexical contours of the nested procedure activations on the stack. I imagine that this is what has led to the name. (ii)    It is a shame that the same attribute is used to mark all compiler generated classes as it makes it hard to figure out what they are being used for. Indeed, you could imagine optimisations that the runtime could perform if it knew that classes corresponded to certain high level concepts. We can see that the local variable generator has been turned into a field in the class, and the body of the lambda expression has been turned into a method of the new class. The code that builds the Func object simply constructs an instance of this class and initialises the fields to their initial values.     c__DisplayClass1 class2 = new c__DisplayClass1();     class2.generator = new Random();     Func func = new Func(class2.b__0); Reflector already contains code to spot this pattern of code and reproduce the form containing the lambda expression, so this is example is correctly decompiled. The use of compiler generated code is even more spectacular in the case of iterators. C# introduced the idea of a method that could automatically store its state between calls, so that it can pick up where it left off. The code can express the logical flow with yield return and yield break denoting places where the method should return a particular value and be prepared to resume.         {             yield return 1;             yield return 2;             yield return 3;         } Of course, there was already a .NET pattern for expressing the idea of returning a sequence of values with the computation proceeding lazily (in the sense that the work for the next value is executed on demand). This is expressed by the IEnumerable interface with its Current property for fetching the current value and the MoveNext method for forcing the computation of the next value. The sequence is terminated when this method returns false. The C# compiler links these two ideas together so that an IEnumerator returning method using the yield keyword causes the compiler to produce the implementation of an Iterator. Take the following piece of code.         IEnumerable GetItems()         {             yield return 1;             yield return 2;             yield return 3;         } The compiler implements this by defining a new class that implements a state machine. This has an integer state that records which yield point we should go to if we are resumed. It also has a field that records the Current value of the enumerator and a field for recording the thread. This latter value is used for optimising the creation of iterator instances. [CompilerGenerated] private sealed class d__0 : IEnumerable, IEnumerable, IEnumerator, IEnumerator, IDisposable {     // Fields     private int 1__state;     private int 2__current;     public Program 4__this;     private int l__initialThreadId; The body gets converted into the code to construct and initialize this new class. private IEnumerable GetItems() {     d__0 d__ = new d__0(-2);     d__.4__this = this;     return d__; } When the class is constructed we set the state, which was passed through as -2 and the current thread. public d__0(int 1__state) {     this.1__state = 1__state;     this.l__initialThreadId = Thread.CurrentThread.ManagedThreadId; } The state needs to be set to 0 to represent a valid enumerator and this is done in the GetEnumerator method which optimises for the usual case where the returned enumerator is only used once. IEnumerator IEnumerable.GetEnumerator() {     if ((Thread.CurrentThread.ManagedThreadId == this.l__initialThreadId)               && (this.1__state == -2))     {         this.1__state = 0;         return this;     } The state machine itself is implemented inside the MoveNext method. private bool MoveNext() {     switch (this.1__state)     {         case 0:             this.1__state = -1;             this.2__current = 1;             this.1__state = 1;             return true;         case 1:             this.1__state = -1;             this.2__current = 2;             this.1__state = 2;             return true;         case 2:             this.1__state = -1;             this.2__current = 3;             this.1__state = 3;             return true;         case 3:             this.1__state = -1;             break;     }     return false; } At each stage, the current value of the state is used to determine how far we got, and then we generate the next value which we return after recording the next state. Finally we return false from the MoveNext to signify the end of the sequence. Of course, that example was really simple. The original method body didn't have any local variables. Any local variables need to live between the calls to MoveNext and so they need to be transformed into fields in much the same way that we did in the case of the lambda expression. More complicated MoveNext methods are required to deal with resources that need to be disposed when the iterator finishes, and sometimes the compiler uses a temporary variable to hold the return value. Why all of this explanation? We've implemented the de-compilation of iterators in the current EAP version of Reflector (7). This contrasts with previous version where all you could do was look at the MoveNext method and try to figure out the control flow. There's a fair amount of things we have to do. We have to spot the use of a CompilerGenerated class which implements the Enumerator pattern. We need to go to the class and figure out the fields corresponding to the local variables. We then need to go to the MoveNext method and try to break it into the various possible states and spot the state transitions. We can then take these pieces and put them back together into an object model that uses yield return to show the transition points. After that Reflector can carry on optimising using its usual optimisations. The pattern matching is currently a little too sensitive to changes in the code generation, and we only do a limited analysis of the MoveNext method to determine use of the compiler generated fields. In some ways, it is a pity that iterators are compiled away and there is no metadata that reflects the original intent. Without it, we are always going to dependent on our knowledge of the compiler's implementation. For example, we have noticed that the Async CTP changes the way that iterators are code generated, so we'll have to do some more work to support that. However, with that warning in place, we seem to do a reasonable job of decompiling the iterators that are built into the framework. Hopefully, the EAP will give us a chance to find examples where we don't spot the pattern correctly or regenerate the wrong code, and we can improve things. Please give it a go, and report any problems.

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  • method to change apache config via the shell with whm/cpanel

    - by Chiggsy
    How can I make changes to the apache config on a whm/cpanel setup from the shell and have them integrate properly? I read the theory of the config system and regardless of my feelings on the matter I understand where they are coming from. Still, in that world view, there must be a way to interact with the system from a command line interface, right?

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