.NET/Java PDF, Tiff, Barcode SDK Library

y now, you may have noticed that a fair amount of plumbing is involved in programming with Ajax If you have to support multiple browsers (and who doesn t these days ), you will inevitably run into incompatibilities Just look at the simple act of creating an instance of the XMLHttpRequest object it requires a browser test As soon as you start experimenting with Ajax techniques, you will quickly notice that you are performing the same tasks repeatedly Of course, you ll probably put together some libraries of common code, or maybe you ll even create your own framework Before you do, though, you may want to take a look at what s already available Like any good technology, Ajax has already spawned a number of frameworks to make life easier for mere mortals We want to stress that Ajax is new and dynamic so too is the framework landscape.

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// helper function to run the test to let runTest (f : unit -> Thread) message = print_endline message; let t1 = f() in let t2 = f() in t1Start() t2Start() t1Join() t2Join() // runs the demonstrations let main() = runTest makeUnsafeThread "Running test without locking .." runTest makeSafeThread "Running test with locking .." main () The part of the example that actually uses the lock is repeated next to highlight the important points You should note a couple of important factors First, the declaration of the lockObj will be used to create the critical section Second, the use of the lock function is embedded in the makeSafeThread function The most important thing to notice is how the printing functions you want to be atomic are placed inside the function that is passed to lock.

NXT-G is the programming language that comes with the NXT. Its integrated development environment (IDE) window looks like Figure 2-1. The language is highly graphical, consisting of blocks that perform operations such as input, output, computation, and execution flow. You can download your NXT-G program to the NXT and perform other maintenance functions from the same environment.

// the object that will be used as a lock let lockObj = new Object() // create a thread that prints to the console in a safe way let makeSafeThread() = new Thread(fun () -> for x = 1 to 100 do // use lock to ensure operation is atomic lock lockObj (fun () -> printSlowly "One .. Two .. Three .. " print_newline() ) done) The results of the first part of the test will vary each time it is run, since it depends on when a thread context switches It might also vary based on the number of processors, because if a machine has two or more processors, then threads can run at the same time, and therefore the messages will be more tightly interspersed On a single-processor machine, things will look less messy, because the messages will go wrong only when a content switch takes place.

New entrants appear seemingly daily, and right now none is a clear winner Few of the frameworks existed before mid-2003, so expect to see significant changes in the coming months Some frameworks are based on the client side, and some are based on the server side Some are designed for specific languages, and others are language agnostic The majority have open-source implementations, but a few are proprietary We won t cover every framework, and we certainly won t go into a great deal of depth on the ones we do touch on; still, we wanted to give you a flavor of what is available By the time you read this appendix, some of the toolkits mentioned will be dormant, and others will have been created Which framework is right for you Only you can say; however, you may want to take a conservative stance until the framework area solidifies.

The results of the first part of the sample, run on a single-processor machine, are as follows:.

Figure 2-1. NXT-G programming environment Data is passed from block to block on data wires. For example, the first block in the program shown in Figure 2-2 is a Light Sensor. The light level as a percent number (0 to 100) is being passed to the Number block, to the Text block, and also to a Math block. The part of the block that sticks down from the icon is called the data hub. You can minimize the blocks to show only the inputs and outputs that are being used by clicking the top of the data hub.

An effort is even underway to merge the various frameworks together it ll be interesting to see how this plays out! By the time you read this, the picture should be clearer, but you will want to keep a close eye on this space..