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  • How to convert 3GP video for Android to view?

    - by RedNax
    Hi, I'm creating 3GP videos with the Android - however, when the 3GP files are posted on a site, the same Android phone cannot view it back. (The file works on the iPhone). What is right way to encode/resize the 3GP video so that the video player on Android can play it back? Thanks

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  • ASP.NET MVC - how to get the value from a textbox in my View?

    - by fearofawhackplanet
    If I have a textbox in my view: <div><%= Html.TextBox("Comments", Model.Comments)%></div> I want to post the contents of this textbox to the controller with an Ajax call. I only need this one value though, so I don't want to post the whole form back. <%= Ajax.ActionLink("update", "UpdateComments", new { comments = /* ????? */ }, new AjaxOptions { HttpMethod="POST" })%> How do I get the textbox value?

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  • PHP coding - A class for each view or one class to rule them all?

    - by Kyle
    I am starting my first "programming" project in PHP making some sort of web application that give the linux program, Motion, a decent web interface. Anyways, I was curious as to how when real applications are programmed, do y'all go for a class for each view or one single class for the application altogether? I know this is more of a preference thing, I was just curious as to how it happens in real software.

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  • How to automate the java Applet(tree view) from my .NET application.

    - by rajeev-vj
    Hi I have a java applet (tree view) on Internet Explorer. when i Click on this applet (+) it collapes, as the information is based on this plus sign. I need to automate this java applet to click automatically from my C#.NET winforms application but am not able to get the details of the java applet. How to get the details of the java applet from browser and how to automate the java applet? Thanks

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  • How can I view the source code for a particular `predict` function?

    - by merlin2011
    Based on the documentation, predict is a polymorphic function in R and a different function is actually called depending on what is passed as the first argument. However, the documentation does not give any information about the names of the functions that predict actually invokes for any particular class. Normally, one could type the name of a function to get its source, but this does not work with predict. If I want to view the source code for the predict function when invoked on objects of the type glmnet, what is the easiest way?

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  • Using Razor together with ASP.NET Web API

    - by Fredrik N
    On the blog post “If Then, If Then, If Then, MVC” I found the following code example: [HttpGet]public ActionResult List() { var list = new[] { "John", "Pete", "Ben" }; if (Request.AcceptTypes.Contains("application/json")) { return Json(list, JsonRequestBehavior.AllowGet); } if (Request.IsAjaxRequest()) [ return PartialView("_List", list); } return View(list); } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } The code is a ASP.NET MVC Controller where it reuse the same “business” code but returns JSON if the request require JSON, a partial view when the request is an AJAX request or a normal ASP.NET MVC View. The above code may have several reasons to be changed, and also do several things, the code is not closed for modifications. To extend the code with a new way of presenting the model, the code need to be modified. So I started to think about how the above code could be rewritten so it will follow the Single Responsibility and open-close principle. I came up with the following result and with the use of ASP.NET Web API: public String[] Get() { return new[] { "John", "Pete", "Ben" }; } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   It just returns the model, nothing more. The code will do one thing and it will do it well. But it will not solve the problem when it comes to return Views. If we use the ASP.NET Web Api we can get the result as JSON or XML, but not as a partial view or as a ASP.NET MVC view. Wouldn’t it be nice if we could do the following against the Get() method?   Accept: application/json JSON will be returned – Already part of the Web API   Accept: text/html Returns the model as HTML by using a View   The best thing, it’s possible!   By using the RazorEngine I created a custom MediaTypeFormatter (RazorFormatter, code at the end of this blog post) and associate it with the media type “text/html”. I decided to use convention before configuration to decide which Razor view should be used to render the model. To register the formatter I added the following code to Global.asax: GlobalConfiguration.Configuration.Formatters.Add(new RazorFormatter()); Here is an example of a ApiController that just simply returns a model: using System.Web.Http; namespace WebApiRazor.Controllers { public class CustomersController : ApiController { // GET api/values public Customer Get() { return new Customer { Name = "John Doe", Country = "Sweden" }; } } public class Customer { public string Name { get; set; } public string Country { get; set; } } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Because I decided to use convention before configuration I only need to add a view with the same name as the model, Customer.cshtml, here is the example of the View:   <!DOCTYPE html> <html> <head> <script src="http://ajax.aspnetcdn.com/ajax/jquery/jquery-1.5.1.min.js" type="text/javascript"></script> </head> <body> <div id="body"> <section> <div> <hgroup> <h1>Welcome '@Model.Name' to ASP.NET Web API Razor Formatter!</h1> </hgroup> </div> <p> Using the same URL "api/values" but using AJAX: <button>Press to show content!</button> </p> <p> </p> </section> </div> </body> <script type="text/javascript"> $("button").click(function () { $.ajax({ url: '/api/values', type: "GET", contentType: "application/json; charset=utf-8", success: function(data, status, xhr) { alert(data.Name); }, error: function(xhr, status, error) { alert(error); }}); }); </script> </html> .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Now when I open up a browser and enter the following URL: http://localhost/api/customers the above View will be displayed and it will render the model the ApiController returns. If I use Ajax against the same ApiController with the content type set to “json”, the ApiController will now return the model as JSON. Here is a part of a really early prototype of the Razor formatter (The code is far from perfect, just use it for testing). I will rewrite the code and also make it possible to specify an attribute to the returned model, so it can decide which view to be used when the media type is “text/html”, but by default the formatter will use convention: using System; using System.Net.Http.Formatting; namespace WebApiRazor.Models { using System.IO; using System.Net; using System.Net.Http.Headers; using System.Reflection; using System.Threading.Tasks; using RazorEngine; public class RazorFormatter : MediaTypeFormatter { public RazorFormatter() { SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html")); SupportedMediaTypes.Add(new MediaTypeHeaderValue("application/xhtml+xml")); } //... public override Task WriteToStreamAsync( Type type, object value, Stream stream, HttpContentHeaders contentHeaders, TransportContext transportContext) { var task = Task.Factory.StartNew(() => { var viewPath = // Get path to the view by the name of the type var template = File.ReadAllText(viewPath); Razor.Compile(template, type, type.Name); var razor = Razor.Run(type.Name, value); var buf = System.Text.Encoding.Default.GetBytes(razor); stream.Write(buf, 0, buf.Length); stream.Flush(); }); return task; } } } .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; }   Summary By using formatters and the ASP.NET Web API we can easily just extend our code without doing any changes to our ApiControllers when we want to return a new format. This blog post just showed how we can extend the Web API to use Razor to format a returned model into HTML.   If you want to know when I will post more blog posts, please feel free to follow me on twitter:   @fredrikn

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  • Silverlight Cream Top Posted Authors June to November, 2010

    - by Dave Campbell
    It's just past the first of December, but I've been busy and it's now time to recognize devs that have a large number of posts in Silverlight Cream. Ground Rules I pick what posts are on the blog Only posts that go in the database are included The author has to appear in SC at least 4 of the 6 months considered I averaged the monthly posts and am only showing Authors with an average greater than 1. Here are the Top Posted Authors at Silverlight Cream for June 1, 2010 through November 30, 2010: It is my intention to post a new list sometime shortly after the 1st of every month to recognize the top posted in the previous 6 months, so next up is January 1! Some other metrics for Silverlight Cream: At the time of this posting there are 7087 articles aggregated and searchable by partial Author, partial Title, keywords (in the synopsis), or partial URL. There are also 116 tags by which the articles can be searched. At the time of this posting there are 664 articles tagged wp7dev. Stay in the 'Light!

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  • ASP.NET MVC Framework

    - by Aamir Hasan
     MVC is a design pattern. A reusable "recipe" for constructing your application. Generally, you don't want your user interface code and data access code to be mixed together, it makes changing either one more difficult. By placing data access code into a "Model" object and user interface code into a "View" object, you can use a "Controller" object to act as a go-between, sending messages/calling methods on the view object when the data changes and vice versa. Model-view-controller (MVC) is an architectural pattern used in software engineering. In complex computer applications that present a large amount of data to the user, a developer often wishes to separate data (model) and user interface (view) concerns, so that changes to the user interface will not affect data handling, and that the data can be reorganized without changing the user interface. The model-view-controller solves this problem by decoupling data access and business logic from data presentation and user interaction, by introducing an intermediate component: the controller.Model:    The domain-specific representation of the information that the application operates. Domain logic adds meaning to raw data (e.g., calculating whether today is the user's birthday, or the totals, taxes, and shipping charges for shopping cart items).    Many applications use a persistent storage mechanism (such as a database) to store data. MVC does not specifically mention the data access layer because it is understood to be underneath or encapsulated by the Model.View:    Renders the model into a form suitable for interaction, typically a user interface element. Multiple views can exist for a single model for different purposes.Controller:    Processes and responds to events, typically user actions, and may invoke changes on the model.    

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  • Excessive CPU Utilization for Bind 9.8.1 `named` processes

    - by justinzane
    I just noticed that named is eating vast amounts of CPU time for a very small network with only a few domains. Can someone help me determine what is misconfigured, please? Or how to debug this. top top - 14:13:08 up 25 days, 14:16, 1 user, load average: 1.04, 1.04, 1.05 Tasks: 149 total, 1 running, 148 sleeping, 0 stopped, 0 zombie %Cpu(s): 17.3 us, 4.3 sy, 0.0 ni, 78.2 id, 0.1 wa, 0.0 hi, 0.0 si, 0.0 st KiB Mem: 2042776 total, 1347916 used, 694860 free, 249396 buffers KiB Swap: 3976080 total, 30552 used, 3945528 free, 574164 cached PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 17445 bind 20 0 244m 42m 3124 S 99.4 2.2 2345:03 named rndc stats +++ Statistics Dump +++ (1352931389) ++ Incoming Requests ++ 65869 QUERY ++ Incoming Queries ++ 31809 A 241 NS 3 CNAME 27455 SOA 276 PTR 123 MX 462 TXT 5400 AAAA 7 A6 1 DS 14 DNSKEY 15 SPF 55 AXFR 8 ANY ++ Outgoing Queries ++ [View: internal] 22206 A 509 NS 10 SOA 25 PTR 12 MX 524 TXT 4851 AAAA 62 DNSKEY 19 SPF 3157 DLV [View: external] 87 A 2 NS 80 AAAA 120 DNSKEY 7 DLV [View: _bind] ++ Name Server Statistics ++ 65869 IPv4 requests received 27670 requests with EDNS(0) received 112 TCP requests received 65652 responses sent 20 truncated responses sent 27670 responses with EDNS(0) sent 62920 queries resulted in successful answer 37117 queries resulted in authoritative answer 28482 queries resulted in non authoritative answer 7 queries resulted in referral answer 591 queries resulted in nxrrset 53 queries resulted in SERVFAIL 2081 queries resulted in NXDOMAIN 14530 queries caused recursion 162 duplicate queries received 55 requested transfers completed ++ Zone Maintenance Statistics ++ 109536 IPv4 notifies sent ++ Resolver Statistics ++ [Common] [View: internal] 29362 IPv4 queries sent 2013 IPv6 queries sent 28531 IPv4 responses received 4209 NXDOMAIN received 6 SERVFAIL received 31 FORMERR received 32 EDNS(0) query failures 3359 query retries 836 query timeouts 5348 IPv4 NS address fetches 3271 IPv6 NS address fetches 83 IPv4 NS address fetch failed 2779 IPv6 NS address fetch failed 17421 DNSSEC validation attempted 12731 DNSSEC validation succeeded 4690 DNSSEC NX validation succeeded 21104 queries with RTT 10-100ms 7418 queries with RTT 100-500ms 3 queries with RTT 500-800ms 1 queries with RTT 800-1600ms [View: external] 192 IPv4 queries sent 104 IPv6 queries sent 192 IPv4 responses received 2 NXDOMAIN received 104 query retries 44 IPv4 NS address fetches 44 IPv6 NS address fetches 1 IPv4 NS address fetch failed 1 IPv6 NS address fetch failed 4 DNSSEC validation attempted 3 DNSSEC validation succeeded 1 DNSSEC NX validation succeeded 152 queries with RTT 10-100ms 40 queries with RTT 100-500ms [View: _bind] ++ Cache DB RRsets ++ [View: internal (Cache: internal)] 2007 A 652 NS 131 CNAME 1 MX 32 TXT 421 AAAA 28 DS 244 RRSIG 110 NSEC 3 DNSKEY 2 !A 2 !TXT 89 !AAAA 2 !SPF 14 !DLV 148 NXDOMAIN [View: external (Cache: external)] 55 A 12 NS 34 AAAA 2 DS 10 RRSIG 1 DNSKEY [View: _bind (Cache: _bind)] ++ Socket I/O Statistics ++ 82958 UDP/IPv4 sockets opened 2118 UDP/IPv6 sockets opened 4 TCP/IPv4 sockets opened 1 TCP/IPv6 sockets opened 82956 UDP/IPv4 sockets closed 2117 UDP/IPv6 sockets closed 58 TCP/IPv4 sockets closed 15 UDP/IPv4 socket bind failures 2117 UDP/IPv6 socket connect failures 29554 UDP/IPv4 connections established 59 TCP/IPv4 connections accepted 2117 UDP/IPv6 send errors 5 UDP/IPv4 recv errors ++ Per Zone Query Statistics ++ --- Statistics Dump --- (1352931389)

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  • PTLQueue : a scalable bounded-capacity MPMC queue

    - by Dave
    Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

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  • Ruby Shoes for non-trivial apps

    - by marcof
    I've been taking a look at Ruby Shoes for GUI development with Ruby. So far, it's been a pretty good experience for making simple apps. However, I am quite worried about being able to write large scale applications with it. For example, how would I go about using MVP pattern with this framework ? For now, I have not been able to not make presentation concerns leak into the view because of the lack of some kind of "data binding". I have code that looks like this : Shoes.app do @view = SampleView.new @presenter = SamplePresenter.new @view @label = para @view.sample_property button "Update sample_property" do @presenter.update_sample_property end end Here, the call to @presenter.update_sample_property updates @view.sample_property but the label is not updated accordingly. For this to work, I would have to make @presenter.update_sample_property to return a string, and then call @label.text = return_value, but I think that would violate the MVP principle of not having presentation logic in the view. I'm used to work in .Net with the MVP pattern so I don't know if the pattern applies correctly to Shoes like I tried to do. Are there any ressources out there for making non-trivial apps with Shoes ? Especially using the MVP pattern or something similar ? EDIT : I took a look at the shoebox to see what other people have achieved with the framework. Though I did not look through it extensively, at first sight it seems like they are all simple projects with no real purposes.

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  • Make windows vista file explorer act normally

    - by user25866
    Is there some file I can remove or something I can do to globally ensure that windows visa/xp/etc doesn't do annoying things? Annoying things: 1) Hide the file extension 2) All these "meta" columns I could care less about in "details" view (rating, album, date taken, Assistant's name, Artist, 35mm focal length, City, Other City, etc...). All I want are Name, size, date created, date modified, and file extension. MAYBE file chmod settings. 3) That garbage in the left pane known as "favorite links." (Documents, desktop, photos, music, etc...) 4) Switching between detail view, large icon view, thumbnail view, list view, and tiles when I goto differnt folders, all I want is detail view, with the same columns every time. That's it. I shouldn't have to get third party software to make my file system browseable, but if I need to so be it... Why are all these settings buried away? It feels like I have to apply them onto each folder every time.

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  • MVVM - child windows and data contexts

    - by GlenH7
    Should a child window have it's own data context (View-Model) or use the data context of the parent? More broadly, should each View have its own View-Model? Are there are any rules to guide making that decision? What if the various View-Models will be accessing the same Model? I haven't been able to find any consistent guidance on my question. The MS definition of MVVM appears to be silent on child windows. For one example, I have created a warning message notification View. It really didn't need a data context since it was passed the message to display. But if I needed to fancy it up a bit, I would have tapped the parent's data context. I have run into another scenario that needs a child window and is more complicated than the notification box. The parent's View-Model is already getting cluttered, so I had planned on generating a dedicated VM for the child window. But I can't find any guidance on whether this is a good idea or what the potential consequences may be. FWIW, I happen to be working in Silverlight, but I don't know that this question is strictly a Silverlight issue.

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