Free as Freedom, not Free as Free Pizza!” />
Udruženje Informatičara BiH - Cross-platform and Portable Development With PHP, LAMP/WAMP development, AJAX and Javascript, ASP, dot NET, C sharp, C++, C, VB, Oracle, tutorials and tips...Free as Freedom, not Free as Free Pizza!
Apple today unveiled its new MacBook featuring Intel Core 2 Duo processors and offering double the memory as well as greater storage capacity than the previous generation. The one-inch thin laptops are up to 25 percent faster than the previous generation, according to Apple, and maintain the built-in iSight video camera for on-the-go video conference ... [more]
posted by NurAzije - Ashraf Gheith @ 4:07 PM
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Today I will talk about a popular bug in AJAX, if you use AJAX on your site and you have a slow server you will encounter this problem, it is the problem when Firefox freezes out and do not do anything if you request an AJAX before the last one ends, if you view it in a debugger we will have this error line “component returned failure code 0xc1f30001 (ns_error_not_initialized)”...
First let us take a look at the problem, I do not want to give you a direct solution so you can copy and paste it, I will give it you at end, but let us see what is the problem. AJAX is a request from the client-side to the server-side without reloading the page, so if we use AJAX it will send a request in the background and receive what we need, and by using JavaScript elementary code it will change the content of our page. Because AJAX is a JavaScript in the first place, it will not work on JavaScript disabled browsers, so please check if your browser is blocking JavaScript, then continue with us.
As a JavaScript code, AJAX will make first a request object, this object depends if our browser is an IE or other browser, so we mostly make a function which will test which browser we are using and then call the right object. Why we are talking about the object? It is because it is the cause of the bug, and let me tel you how. When the browser sends a request we are using this object, and we can not use it in the same time until we finish using it, so if we call it we got the error we have, so we must wait for the end of it's process and then send the next request. If we are working on a slow server or with a slow connection, the client will have a problem, and the application will not work, so we need to somehow fix this problem.
The solution will be simple, logically we need a second object which will not conflict the first, and third which will not conflict the first two, and so on ... How ?
Simple, we make a unique object every time we request a page. We can use an Array of objects, so every time we request an object we auto increment our array and use it's address to follow the request, let me show you by an example:
function createRequestObject()
{
var request_;
var browser = navigator.appName;
if(browser == "Microsoft Internet Explorer")
{
request_ = new ActiveXObject("Microsoft.XMLHTTP");
}else{
request_ = new XMLHttpRequest();
}
return request_;
}
var http = new Array();
function getInfo(){
var curDateTime = new Date();
http[curDateTime] = createRequestObject();
http[curDateTime].open(\'get\', \'refresh.php\');
http[curDateTime].onreadystatechange = function()
{
if (http[curDateTime].readyState == 4)
{
if (http[curDateTime].status == 200 || http[curDateTime].status == 304)
{
var response = http[curDateTime].responseText;
document.getElementById(\'view_ajax\').innerHTML = response;
}
}
}
http[curDateTime].send(null);
}
As you can see, we will create an array “http” which will carry the object, then in the request we make a unique string, we can use the time, because it is always unique from the before “var curDateTime = new Date();”, and then we call the function and create the request in the array as a unique key for it “http[curDateTime] = createRequestObject();” ...
This is how simply we can beat this bug, no need to wait Firefox to fix this bug..
posted by NurAzije - Ashraf Gheith @ 3:36 PM
2 comments
Over at Riya’s Like.com, interesting things have been happening. The site now presents a visual search engine that looks for the likeness of two given pictures. For example, they show off how they kind find a specific handbags within a set of celebrity photos.
I got some errors – a file-not-found pointing to shopping.riya.com, and I also you also can’t zoom into pics using their rectangle functionality for the first minute or so when you load a page – but this looks like an interesting twist to image search. Right now Like.com is restricted to pre-selected fashion items, though... this would get really cool only if I’m allowed to upload my own pics to search for similar pics on the web.
posted by NurAzije - Ashraf Gheith @ 2:20 PM
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posted by NurAzije - Ashraf Gheith @ 2:02 PM
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November 08, 2006 (IDG News Service) -- Google Inc. wants to make the information it stores for its users easily portable so they can export it to a competing service if they are dissatisfied, the company's CEO said yesterday.
posted by NurAzije - Ashraf Gheith @ 1:05 PM
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osted by: Joseph Ottinger on November 08, 2006
posted by NurAzije - Ashraf Gheith @ 12:37 PM
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Belkin’s so-called Cable-Free USB Hub (MSRP $130) will use ultrawideband (UWB) to allow driver-free connections by pairing a UWB dongle that plugs into a USB port on a host computer with a four-port AC-powered hub that can be located elsewhere in a room. In the press release for this award, Belkin doesn’t provide an expected shipping date.
Belkin was originally planning to release this in early 2006, and demonstrated prototypes (or at least brick-o-types: nonfunctioning plastic models) at CES and Macworld Expo. Their first design was based on Freescale’s UWB chips, which have not yet appeared in a shipping product. Freescale was sold to an investment consortium recently, and I have expected to see their UWB line dropped in favor of a focus on the company’s vast array of revenue-generating, already-shipping technology.
In summer, reports appeared (that Belkin later confirmed) that the company was shifting from Freescale to a vendor that’s part of the Intel-led, 200-member-strong WiMedia Alliance. Belkin noted today in their press release that they would use technology from Wisair. Wisair has a USB hub reference design that will obviously be the basis for Belkin’s product. Reference designs are generally fully developed products ready for customization. Because this hub is driver-free, there’s really nothing beyond an injection-molded case and some logo silkscreening that needs to be added.
(I said that Belkin’s hub was “so-called” because Cable-Free is Freescale’s term for USB over UWB; the WiMedia Alliance has a partnership with the USB Implementers Forum, and Wireless USB is the trademarked and supported term that those two organizations will push for USB over UWB. Belkin might change the name for this reason.)
posted by NurAzije - Ashraf Gheith @ 9:26 AM
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Firefox 2.0 is not the only web browser that can auto-discover how a site can be searched (see Firefox 2.0 Open Search Discovering Simpy). Have a look at the screenshot below:
posted by NurAzije - Ashraf Gheith @ 9:23 AM
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Posted by: Dave MacLachlan, Member of Technical Staff, Mac Team
@synchronized block around a shared resource we were using:
+(id)fooFerBar:(id)bar {
@synchronized(self) {
static NSDictionary *foo = nil;
if (!foo) foo = [NSDictionary dictionaryWithObjects:...];
}
return [foo objectWithKey:bar];
}
@synchronized block each of the millions of times we were calling fooFerBar. We couldn't create the resource in +initialize, because fooFerBar was part of a category, and overriding +initialize in a category is a bad thing. We also couldn't use +load, because other classes could have easily called fooFerBar in their +load, and there's no guarantee on loading order. So our only choice was to minimize the impact of that @synchronized block, and we didn't want to run into the infamous and dreaded double-checked locking anti-pattern.@synchronized work? And is there a cheaper way of getting the same thread-safe result? I disassembled the code to find out what @synchronized does, and I saw something like this:
...
objc_sync_enter
objc_exception_try_enter
setjmp
objc_exception_extract
my actual code
objc_exception_try_exit
objc_sync_exit
...
objc_exception_throw
...
@synchronized give us a lock, but it's a recursive lock, which is overkill for this particular usage.objc_sync_enter and obc_sync_exit, we can see that on every @synchronized(foo) block, we are actually paying for 3 lock/unlock sequences. objc_sync_enter calls id2data, which is responsible for getting the lock associated with foo, and then locks it. objc_sync_exit also calls id2data to get the lock associated with foo, and then unlocks it. And, id2data must lock/unlock its own internal data structures so that it can safely get the lock associated with foo, so we pay for that on each call as well.@synchronized call, and wrap our code with some pthread locks instead.
#include
+(id)fooFerBar:(id)bar {
static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
if (pthread_mutex_lock(&mtx)) {
printf("lock failed sigh...");
exit(-1);
}
static NSDictionary *foo = nil;
if (!foo) foo = [NSDictionary dictionaryWithObjects:...];
if (pthread_mutex_unlock(&mtx) != 0)) {
printf("unlock failed sigh...");
exit(-1);
}
return [foo objectWithKey:bar];
}
-fno-threadsafe-statics option to the compiler.
+(id)fooFerBar:(id)bar {
static NSDictionary *foo = [NSDictionary dictionaryWithObjects:...];
return [foo objectWithKey:bar];
}
cxa_guard_acquire
my actual code
cxa_guard_release
cxa_guard_abort
Unwind_Resume
...
-fno-threadsafe-statics in a threaded environment, in which case we're asking for trouble, and trouble will certainly follow (we won't do that).@synchronized with C++ dynamic initialization of local statics?
+(id)fooFerBar:(id)bar {
@synchronized(self) {
static NSDictionary *foo = [NSDictionary dictionaryWithObjects:...];
return [foo objectWithKey:bar];
}
}
...
objc_sync_enter
objc_exception_try_enter
setjmp
objc_exception_extract
cxa_guard_acquire
my actual code
cxa_guard_release
cxa_guard_abort
objc_exception_try_exit
objc_sync_exit
objc_exception_throw
...
static NSDictionary *foo = nil;
+(id)fooFerBar:(id)bar {
@synchronized(self) {
if (!foo) foo = [NSDictionary dictionaryWithObjects:...];
ReplaceMethodImplementationWithSelector
([self class], @selector(fooFerBar), @selector(fooFerBar2));
}
return [foo objectWithKey:bar];
}
+(id)fooFerBar2:(id)bar {
return [foo objectWithKey:bar];
}
ReplaceMethodImplementationWithSelector swizzles fooFerBar with fooFerBar2. So, the first time fooFerBar is called we get our slow case, and any later calls get the fast case, assuming the first thread has completed fooFerBar. This solution provides great performance, and you only have to pay for the synchronize once. Very nice!
posted by NurAzije - Ashraf Gheith @ 9:21 AM
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Dell's new OptiPlex workstations feature AMD and Intel power
The OptiPlex 740 features AMD's Athlon 64 X2 dual-core processors while the OptiPlex 320 uses Intel Pentium D dual-core processors. Both systems feature:
The OptiPlex 740 will start at $725 while the OptiPlex 320 starts at $585 with a Pentium D 820 processor. Both feature a standard 3-year limited warranty and next-business day on-site warranty service.
With Dell continuing to open the floodgates with more AMD-based products, the current chip shortage that is affecting some AMD partners isn’t likely to get better any time soon. Many smaller system builders and some of AMD’s largest distributors are really feeling the pinch and they are seeing dwindling stocks of popular AMD processors.
posted by NurAzije - Ashraf Gheith @ 9:06 AM
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Are e-voting machines mistakenly giving votes to the wrong candidates?
November 08, 2006 (Computerworld) -- During Tuesday's midterm elections in the U.S., reports emerged from across the nation about a problem called "vote-flipping," where a voter selected a candidate on e-voting hardware -- and the machine counted the vote for an opposing candidate.
The problem has ben reported in U.S. elections since 2004 as more states move to e-voting machines that are supposed to make the vote counting process more accurate. Instead, for many Americans, the process has led to more questions than answers, and suspicions that their votes aren't being counted correctly.
Stanford University computer science professor David L. Dill, who founded the nonprofit Verified Voting Foundation and VerifiedVoting.org, has been looking at vote flipping and yesterday called for investigations to stop the problem.
"People have been way too quick to diagnose the problem," Dill said. Some who have not examined the issue closely quickly call it a touchscreen calibration problem, others point to different causes. "It could be a calibration problem with the touchscreens, but I'm not sure that anyone really knows yet because no one's looked at it. My answer as a computer scientist is that I want facts ... and all I've heard for two years is speculation."
Dill said he's not convinced of one theory -- that the problem is a conspiracy to defraud voters of their votes and give the election to the opposition. Once a voter makes his or her selections on a machine, a review screen shows them for whom their votes will be tallied, which the voter can confirm or at least review. That ability to review the vote before it is ultimately cast, he said, makes it less likely that fraud is involved.
"It seems to me if you were trying to commit fraud, you wouldn't show [the ballot] to the voter," he said.
One of the possible causes of vote flipping may be voters who place their hands on the side of a machine as they vote, perhaps accidentally touching it with their thumb and erroneously making a selection, he said. In other cases, some e-voting machines use a thumb-operated wheel to advance the electronic screens and when it is turned, it highlights a candidate in the next race on the ballot -- possibly giving a voter the impression that an erroneous choice has been made for them, he said.
The way to figure it out, he said, is to bring together a panel of experts to investigate the issue, confirm it, find ways to fix it and then get any fixes out to voting officials, Dill said. Until then, election officials and watchdog groups across the country will continue to hear reports of vote flipping, he said.
"We know it's going to be a major deal," Dill said. If a voter notices the problem on an e-voting machine's review screen, they can try to go back and fix it, he said. Sometimes it takes multiple attempts to correct, according to reports. But if they don't notice it or try to go backward to fix it, their votes are improperly cast, he said.
"This problem, I think, is a national disgrace," Dill said. "There needs to be a serious independent investigation of this problem ... across the country."
Machines that use paper ballots scanned with optical scanning readers are more secure because voters have filled out the ballots themselves and a paper trail is available for any necessary recounts, he said. Although film documentaries are being made about the vote flipping problems -- and potential conspiracy theories -- "I'm not sure I buy that," Dill said. "But we definitely need to get to the bottom of it."
In his home precinct in San Mateo County, Calif., Dill said he voted on an optical scanning machine that automatically "read" the paper ballot he filled out with a pen. He wanted to try one of the new Hart InterCivic eSlate electronic machines the county bought, but the only one in his polling place was in use, he said. The eSlates used by San Mateo County include a paper record of the voter's choices that is printed out, he said.
The machines chosen by his county are not his preference, however. "I have long advocated precinct-scan optical scanning machines" using ballots filled out by voters and then read by scanners.
posted by NurAzije - Ashraf Gheith @ 9:01 AM
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