Simple .NET/ASP.NET PDF document editor web control SDK

, applying a blur effect by smearing nearby pixels into one another), it s possible for different logical processors to be working on different parts of the image Even here you won t get a 4x speedup on a fourcore system, because some coordination might be necessary at the boundaries, and other parts of the system such as memory bandwidth may become a bottleneck, but these sorts of tasks typically see a useful improvement However, these so-called embarrassingly parallel tasks are the exception rather than the rule a lot of computation is sequential in practice And of course, many problems live in a middle ground, where they can exploit parallelism up to a certain point, and no further So there s usually a limit to how far multithreading can help programs execute faster.

barcode for excel 2007 free, barcode font excel 2003, barcode format in excel 2007, create barcode in excel 2007 free, barcode add in excel, free barcode generator for excel 2010, how to create barcodes in excel 2016, excel 2010 microsoft barcode control, barcode generator excel 2010, excel 2010 barcode generator,

That doesn t stop some people from trying to use as many multiple logical processors as possible, or from realizing when doing so has failed to make things better It s easy to be distracted by achieving high CPU usage, when the thing you really want to measure is how quickly you can get useful work done..

It s possible to construct parallel solutions to problems that manage to use all the available CPU time on all logical processors, and yet which proceed more slowly than single-threaded code that does the same job on one logical processor. Figure 16-1 shows the CPU load reported by the Windows Task Manager for two different solutions to the same task. The image on the left might make you feel that you re making better use of your multicore system than the one on right. The righthand side is using far less than half the available CPU capacity. But measuring the elapsed time to complete the task, the code

Figure 3-5. Buttons with stretch factors (left to right: 1, 3, and 2)

addCSSClass(String className) focus() scrollIntoView() removeCSSClass(String className) toggleCSSClass(String className)

that produced the lefthand image took about 15 times longer to complete than the code that produced the righthand one! The job in hand was trivial both examples just increment a field 400 million times. Example 16-8 shows both main loops. The Go function is the one that gets invoked concurrently on four threads. GoSingle just runs multiple times in succession to perform the iterations sequentially.

class Program { static int Count; const int Iterations = 100000000; static void Go() { for (int i = 0; i < Iterations; ++i) { Interlocked.Increment(ref Count); } } static void GoSingle(int repeat) { for (int outer = 0; outer < repeat; ++outer) { for (int i = 0; i < Iterations; ++i) { Count += 1; } } } ...

Here s the code that launches Go concurrently:

Up to now you have looked at size policies and used horizontal and vertical layouts. From Designer you can attain the three most common layouts: horizontal, vertical, and grid. The box layouts (which you have seen several times) are available through the classes QHBoxLayout (horizontal) and QVBoxLayout (vertical). They simply put the widgets in a row or column from left to right or from top-down. Figures 3-6 and 3-7 show both classes in action. In the examples, the widgets were added in this order: foo, bar, baz. When used in combination with stretch factors and size policies, they can be used as a basis for many different dialog layouts.

Count = 0; List<Thread> threads = (from i in Enumerable.Range(0, 4) select new Thread(Go)).ToList(); threads.ForEach(t => t.Start()); threads.ForEach(t => t.Join());

This creates four threads, all of which call Go. Next, it calls Start on each of the threads. Having started them all, it calls Join on each thread to wait for them all to complete. (We could have written three loops here, but our use of LINQ and lambdas makes the code much more compact. In particular, if you have a loop that invokes just one operation on every item in a list the List<T> class s ForEach method is a less cluttered way of expressing this than a foreach loop.) The code to launch the single-threaded version is a lot simpler:

Count = 0; GoSingle(4);

If you need to, you can alter the direction in which widgets are added by using the setDirection Tip

Both produce the same result: the Count field contains 400,000,000 at the end. But the multithreaded version was much slower. One reason is the difference in how the two versions increment the Count. Here s the line in question from the single-threaded code:

Attaches the class specified in className to the anchor. It must be a valid, defined CSS class available to the host page. Passes focus to the anchor. If the anchor is off the page, scrolls the page until it is in view. Unattaches the CSS class specified in className. If the CSS className is currently attached, unattaches it; otherwise, attaches it.

Count += 1;