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  • Exception in Google App Engine (Java) while trying to create Memcache Object

    - by Shreeni
    I am coming back to an old Google App Engine project on which I saw a bug. During this lag, I have been upgrading my AppEngine SDK and is now set at 1.3. When I try to run the same project again, I see the following exception: java.lang.NoSuchMethodError: com.google.apphosting.api.ApiProxy$Environment.getDefaultNamespace()Ljava/lang/String; at com.google.appengine.api.NamespaceManager.get(NamespaceManager.java:56) at com.google.appengine.api.memcache.MemcacheServiceImpl.setNamespace(MemcacheServiceImpl.java:181) at com.google.appengine.api.memcache.MemcacheServiceImpl.(MemcacheServiceImpl.java:145) at com.google.appengine.api.memcache.MemcacheServiceFactory.getMemcacheService(MemcacheServiceFactory.java:25) The line causing the problem is: CacheManager.getInstance().getCacheFactory().createCache(Collections.emptyMap()); (It is the same line as suggested by the AppEngine documentation to create a memcache object. It used to work fine previously. ) Any suggestions on how to fix it?

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  • Can Google Employees See My Saved Google Chrome Passwords?

    - by Jason Fitzpatrick
    Storing your passwords in your web browser seems like a great time saver, but are the passwords secure and inaccessible to others (even employees of the browser company) when squirreled away? Today’s Question & Answer session comes to us courtesy of SuperUser—a subdivision of Stack Exchange, a community-driven grouping of Q&A web sites. The Question SuperUser reader MMA is curious if Google employees have (or could have) access to the passwords he stores in Google Chrome: I understand that we are really tempted to save our passwords in Google Chrome. The likely benefit is two fold, You don’t need to (memorize and) input those long and cryptic passwords. These are available wherever you are once you log in to your Google account. The last point sparked my doubt. Since the password is available anywhere, the storage must in some central location, and this should be at Google. Now, my simple question is, can a Google employee see my passwords? Searching over the Internet revealed several articles/messages. Do you save passwords in Chrome? Maybe you should reconsider: Talks about your passwords being stolen by someone who has access to your computer account. Nothing mentioned about the central storage security and vulnerability. There is even a response from Chrome browser security tech lead about the first issue. Chrome’s insane password security strategy: Mostly along the same line. You can steal password from somebody if you have access to the computer account. How to Steal Passwords Saved in Google Chrome in 5 Simple Steps: Teaches you how to actually perform the act mentioned in the previous two when you have access to somebody else’s account. There are many more (including this one at this site), mostly along the same line, points, counter-points, huge debates. I refrain from mentioning them here, simply carry a search if you want to find them. Coming back to my original query, can a Google employee see my password? Since I can view the password using a simple button, definitely they can be unhashed (decrypted) even if encrypted. This is very different from the passwords saved in Unix-like OS’s where the saved password can never be seen in plain text. They use a one-way encryption algorithm to encrypt your passwords. This encrypted password is then stored in the passwd or shadow file. When you attempt to login, the password you type in is encrypted again and compared with the entry in the file that stores your passwords. If they match, it must be the same password, and you are allowed access. Thus, a superuser can change my password, can block my account, but he can never see my password. So are his concerns well founded or will a little insight dispel his worry? The Answer SuperUser contributor Zeel helps put his mind at ease: Short answer: No* Passwords stored on your local machine can be decrypted by Chrome, as long as your OS user account is logged in. And then you can view those in plain text. At first this seems horrible, but how did you think auto-fill worked? When that password field gets filled in, Chrome must insert the real password into the HTML form element – or else the page wouldn’t work right, and you could not submit the form. And if the connection to the website is not over HTTPS, the plain text is then sent over the internet. In other words, if chrome can’t get the plain text passwords, then they are totally useless. A one way hash is no good, because we need to use them. Now the passwords are in fact encrypted, the only way to get them back to plain text is to have the decryption key. That key is your Google password, or a secondary key you can set up. When you sign into Chrome and sync the Google servers will transmit the encrypted passwords, settings, bookmarks, auto-fill, etc, to your local machine. Here Chrome will decrypt the information and be able to use it. On Google’s end all that info is stored in its encrpyted state, and they do not have the key to decrypt it. Your account password is checked against a hash to log in to Google, and even if you let chrome remember it, that encrypted version is hidden in the same bundle as the other passwords, impossible to access. So an employee could probably grab a dump of the encrypted data, but it wouldn’t do them any good, since they would have no way to use it.* So no, Google employees can not** access your passwords, since they are encrypted on their servers. * However, do not forget that any system that can be accessed by an authorized user can be accessed by an unauthorized user. Some systems are easier to break than other, but none are fail-proof. . . That being said, I think I will trust Google and the millions they spend on security systems, over any other password storage solution. And heck, I’m a wimpy nerd, it would be easier to beat the passwords out of me than break Google’s encryption. ** I am also assuming that there isn’t a person who just happens to work for Google gaining access to your local machine. In that case you are screwed, but employment at Google isn’t actually a factor any more. Moral: Hit Win + L before leaving machine. While we agree with zeel that it’s a pretty safe bet (as long as your computer is not compromised) that your passwords are in fact safe while stored in Chrome, we prefer to encrypt all our logins and passwords in a LastPass vault. Have something to add to the explanation? Sound off in the the comments. Want to read more answers from other tech-savvy Stack Exchange users? Check out the full discussion thread here.     

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  • Hijax == sneaky Javascript redirects? Will I get banned from Google?

    - by Chris Jacob
    Question Will I get penalised as "sneaky Javascript redirects" by Google if I have the following Hijax setup (which requires a JavaScript redirect on the page indexed by google). Goal I want to implement Hijax to enable AJAX content to be accessibile to non-JavaScript users and search engine crawlers. Background I'm working on a static file server (GitHub Pages). No server side tricks allowed (so Google's #! "hash bang" solution is not an option). I'm trying to keep my files DRY. I don't want to repeat the common OUTER template in all my files i.e. header, navigation menu, footer, etc They will live in the main index.html Setup the Hijax index.html page contains all OUTER html/css/js... the site's template. index.html has a <div id="content"> which defaults to containing the "homepage" html. index.html has a navigation menu, with a Hijax link to an "about" page. With JavaScript disabled (e.g. crawler) it follows link to /about.html. With JavaScript enabled (e.g. most people) the link updates the url hash fragment to /#about and jQuery replaces the <div id="content"> innerHTML with $("#content").load("about.html #inner-container");. AJAX content about.html does not contain anything extra to try an cloak content for crawlers. about.html file contains enough HTML / CSS / JavaScript to display /about.html as a standalone page with it's own META data... e.g. <html><head><title>About</title>...</head><body></body></html>. about.html has NO OUTER HTML template (i.e. header, navigation menu, footer, etc). about.html <body> contains a <div id="inner-container"> which holds the content that is injected into index.html. about.html has a <noscript> tag as the first child of <body> which explains to non-JavaScript users that they are viewing the about page "inner content" - with a link to navigate to the index.html page to get the full page layout with menu. The (Sneaky?) Redirect Google indexes the /about.html page. However when a person with JavaScript enabled visits that page there is no OUTER html template (e.g. header, navigation menu, footer, etc). So I need to do a JavaScript redirect to get the person over the /#about page (deeplinking to the "about" page "state" in index.html). I'm thinking of doing a "redirect on click or after 10 seconds". The end results is that user ends up on an "enhanced" page back on index.html with all it's OUTER template - but the core "page" content is practically identical. Known issue with inbound links e.g. Share / Bookmarking It seems that if a user shares the URL /#about on their blog, when allocating inbound links to my site Google ignores everything after the # ... it allocates value to the / page - See: http://stackoverflow.com/questions/5028405/hashbang-vs-hijax/5166665#5166665. I can only try an minimise this issue offering "share" buttons on the page with the appropriate urls i.e. /about.html. Duplicate Sorry. I posted this same question over on http://stackoverflow.com/questions/5561686/hijax-sneaky-javascript-redirects-will-i-get-banned-from-google ... then realised it probably belongs more on this Stack Exchange site... Not sure if I should delete the Stack Overflow question? Or just leave it on both sites? Please leave comment.

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  • Memory leak in Google Chrome

    - by jasondavis
    As a developer it is very common for me to have 2-3 different IDE's open, 10-15 google chrome windows which can hold up to 200 open tabs (I know I get out of hand some times), Photoshop, couple twitter bots for promo, and a few other programs but my system still runs fast and smooth. I have an i7 processor with 12gb ram. Now with all my usual stuff running my Physical memory is usually running around 50-60% however over the course of the day or much less even, I will gradually grow to 98% The highest Memory usage processes will be from Google Chrome, if I sort in the task manager by highest memory usage and end the 1 highest process which will be a google chrome one, my memory usage will jump back down to about 60%. Also by ending that 1 process, all my Chrome windows will remain open and in use, so it doesn't affect me at all by ending that process. Based on this research I am assuming that that 1 runaway process is likely the Adobe Flash as I also can say that it gets up to the 98% much faster when I am using flash items like video or music player. But even without using any of them it will still climb up to that high number eventually. Has anyone else experienced similar results?

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  • IE9 will not navigate to some websites but Google Chrome can

    - by Storchburp
    Was recommended by a friend to ask for help here. I am using Internet Explorer 9. As of two days ago I was suddenly unable to navigate to any part of the following websites: www.computerandvideogames.com www.deviantart.com www.cnet.com However I can still access all of them normally through Google Chrome. I am on a college network but these sites are also accessible through fixed terminals provided by the school and are definitely not blocked. I do not know of any other sites similarly affected. There is no popup, no error message, no diversion to a site telling me I can't access / am blocked etc. I can be on www.google.com and attempt to access these sites through the URL or google search, and my cursor will just show the little moving blue wheel next to the arrow for a couple of seconds, and the page displayed on my browser will not change; ie. not navigating at all. Running antivirus software, changing proxy settings in IE, clearing cookies, unplugging/plugging in computer, restarting PC etc have not changed the situation. Any assistance or advice would be greatly appreciated. Thanks in advance.

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  • Google Desktop Search problems - unable to disable indexing and no index status page

    - by Howiecamp
    I've been running Google Desktop (I've used both the regular and Enterprise versions) without issues on my Windows 7 64-bit PC for a long time with no issues. I just paved my PC and reinstalled Google Desktop (regular edition). Initially, I want to use it only for the CTRL-CTRL launcher capability - I don't want it to do any indexing. So I unchecked all the items in the configuration dialog as well as excluded c:. Despite this, it is indexing all the content on my hard drive as well as Outlook email, etc. In my previous installations I had the same options set and they worked properly. The other problem I have is that when you right-click on the Google Desktop system tray icon, there used to be an option for "Index Status" which showed you the percentage complete the index creation process was, as well as an option to clear and rebuild the index. Those are no longer there. I uninstalled the regular edition and installed the Enterprise Edition, but same problems. Any ideas?

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  • Email bouncing sent from Google

    - by davidmck
    I'm hoping someone here has an idea of where to look next. We have a domain we support which has email sent to it from one particular user bounce with the following message: Delivery to the following recipient failed permanently: [email protected] Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 Unrouteable address (state 14). We only have reports of bouncing form this one particular user (who is someone we don't support - except they'd like to be able to contact our customer and we're trying to figure out if the problem is on our end). Many people can successfully send to this domain and the user who is getting bounce messages can send to other domains that we support (so it's clearly something specific with the princetonscoop.com domain and not our setup in general). I've reviewed the MX records multiple times and the server logs don't show a connection which generates this error (in fact this error is not one that our mail server would ever return). So it appears that google is contacting a different mail server for some reason. I have tested sending from my gmail account and that works. I believe the sender is using a google-apps account (the account they are using is from their own domain, not a gmail account). Any ideas on what might be happening here or what to test/investigate next? Thanks.

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  • Using secure proxies with Google Chrome

    - by cYrus
    Whenever I use a secure proxy with Google Chrome I get ERR_PROXY_CERTIFICATE_INVALID, I tried a lot of different scenarios and versions. The certificate I'm using a self-signed certificate: openssl genrsa -out key.pem 1024 openssl req -new -key key.pem -out request.pem openssl x509 -req -days 30 -in request.pem -signkey key.pem -out certificate.pem Note: this certificate works (with a warning since it's self-signed) when I try to setup a simple HTTPS server. The proxy Then I start a secure proxy on localhost:8080. There are a several ways to accomplish this, I tried: a custom Node.js script; stunnel; node-spdyproxy (OK, this involves SPDY too, but later... the problem is the same); [...] The browser Then I run Google Chrome with: google-chrome --proxy-server=https://localhost:8080 http://superuser.com to load, say, http://superuser.com. The issue All I get is: Error 136 (net::ERR_PROXY_CERTIFICATE_INVALID): Unknown error. in the window, and something like: [13633:13639:1017/182333:ERROR:cert_verify_proc_nss.cc(790)] CERT_PKIXVerifyCert for localhost failed err=-8179 in the console. Note: this is not the big red warning that complains about insecure certificates. Now, I have to admit that I'm quite n00b for what concerns certificates and such, if I'm missing some fundamental points, please let me know.

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  • Spreadsheet functions to query route planner for travel time/distance

    - by Rich
    I would like to achieve something whereby I have a spreadsheet such that the columns are: Column A - place name Column B - place name Column C - distance by road between places in columns A and B Column D - travel time by road between places in columns A and B I thought it might be possible using Google Docs' spreadsheet and its 'Google' functions, but I've not found any that might do the trick. In the end I could knock up an app to do it using the Google Maps API but would rather avoid it if I can.

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  • Google Apps claims my domain is registered but when I try to access it claims it is not

    - by user32953
    Hi all, we have registered one of our domains with Google Apps 2 years ago. However, we didn't even use it. Now if I try to access: http://google.com/a/mydomain.com What I see is: Server error Sorry, you've reached a login page for a domain that isn't using Google Apps. Please check the web address and try again. Then I go to Google Apps Standard Edition signup page and type mydomain.com. However, what I get is: This domain has already been registered with Google Apps. Please contact your domain administrator for instructions on using Google Apps with this domain. Is there anyone who can explain me what this inconsistency is caused by and what I can do? Since Google Apps Standard Edition doesn't grant me to contact with Google, I can't even submit a bug report. Any help would be appreciated.

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  • How to unblacklist an IP at Google?

    - by DJRayon
    I own a small business with two servers for webhosting. When setting up the primary (CentOS 5.5 + WHM, secondary is WHM DNS Only) server I kinda messed up the firewall, so the hackers could send stuff from my server. My primary IP is x.y.29.218. Anyway - I got blacklisted in several places, but now those blacklistings are gone. For a week or so, but Google still has my IP blacklisted. I handling serious damages because of that. Many clients want to switch from my hosting, etc. I've fixed the hole with CSF firewall SMTP_BLOCK option and enabled also the WHM SMTP TEAK Currently all I see from the Main Email View Mail Statistics (Errors section) in WHM is rows and rows of the following message removed-the-email-address-for-security R=lookuphost T=remote_smtp: SMTP error from remote mail server after end of data: host aspmx.l.google.com [a.b.39.27]: 550-5.7.1 [x.y.29.218 1] Our system has detected an unusual rate of\n550-5.7.1 unsolicited mail originating from your IP address. To protect our\n550-5.7.1 users from spam, mail sent from your IP address has been blocked.\n550-5.7.1 Please visit http://www.google.com/mail/help/bulk_mail.html to review\n550 5.7.1 our Bulk Email Senders Guidelines. h24si3868764fas.171 What are my options? I have one IP free. How can I configure Exim to send mail from that IP? My brain is like constantly blowing up because of this problem. Please someone, who has any knowledge how to deal with the current situation, please give me some kind of help - any help, suggestions, etc. I've tried everything I know, and I still don't know much, because this is the first time (I just started to webhost, etc) I deal with real physical servers not some kind of pre-setup VPS solution. Many - many thanks, whoever has time to offer some help.

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  • Google account gives ERR_SSL_BAD_RECORD_MAC_ALERT errors

    - by Kjensen
    A couple of days ago, I started being unable to connect to accounts.google.com, which handles logins to all kinds of google services. I get this error in Chrome: Error 126 (net::ERR_SSL_BAD_RECORD_MAC_ALERT): Unknown error. In IE I get this: I assume it is the same error, just wrapped up. I run Win8 RTM. On the SAME machine, using the same network card, in a VMWare workstation image running Win7, I am able to connect perfectly. On another of my machines on my network, I am also still able to connect with no problem. My girlfriend uses the same network and has also complained a couple of times about this error (google calendar) - but this is anecdotal, since her technical troubleshooting abilities stop at "xxxx is broken". Her machine runs Win7. ;) I have rebooted, cleared cookies, do not run any antivirus/firewall, have not changed network config. The first 3-4 days after installing Win8, I did not have any problems. I have also searched, and found a hint about enabling SSL2.0 in connection settings, which did not help. Anybody know something about this error and what I can do to fix it?

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  • Strange problem with Google Mail and IMAP on Outlook 2007

    - by Alex C.
    I work for a small non-profit organization. We have about 35 administrative employees who use e-mail. We're on a Windows network with a domain. Everyone is running XP Pro and Office 2007 with all updates/patches. We used to use POP3 mail through a local provider. However, we recently signed-up for a free Google Apps account, and we switched to IMAP mail through Google. Everyone uses Outlook 2007 as the client. For about ten days, everything was working fine. Yesterday afternoon, we suddenly developed a strange and annoying problem. Every time you send an e-mail message, a copy of your outgoing message shows up in your inbox. It's as if you're adding your own address to the CC: line of every message. Nothing has changed on our end. I was hoping that the problem was a temporary glitch that would resolve itself, but here we are about 24 hours later, and it's still happening. I searched Twitter, and there were a handful of vague messages about issues with Google mail and IMAP, but I didn't see any references to this specific problem. Any thoughts on what's going on here and how to fix it?

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  • Build tools for php, html, css, js web app development

    - by cs_brandt
    What are some recommendations for a build tool that would allow me to upload changes to a web server or a repository and minify the js and css automatically, and possibly even run Closure compiler on the JavaScript? Im not worried about doing anything with the php code other than update with most recent changes although in the future would like to have phpdoc updated automatically. Just wondering if there is some way to do all this other than an amalgam of scripts that run or have to be invoked every time. Thanks.

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  • Need help regarding one LALR(1) parsing.

    - by AppleGrew
    I am trying to parse a context-free language, called Context Free Art. I have created its parser in Javascript using a YACC-like JS LALR(1) parser generator JSCC. Take the example of following CFA (Context Free Art) code. This code is a valid CFA. startshape A rule A { CIRCLE { s 1} } Notice the A and s in above. s is a command to scale the CIRCLE, but A is just a name of this rule. In the language's grammar I have set s as token SCALE and A comes under token STRING (I have a regular expression to match string and it is at the bottom of of all tokens). This works fine, but in the below case it breaks. startshape s rule s { CIRCLE { s 1} } This too is a perfectly valid code, but since my parser marks s after rule as SCALE token so it errors out saying that it was expecting STRING. Now my question is, if there is any way to re-write the production rules of the parser to account for this? The related production rule is:- rule: RULE STRING '{' buncha_replacements '}' [* rule(%2, 1) *] | RULE STRING RATIONAL '{' buncha_replacements '}' [* rule(%2, 1*%3) *] ; One simple solution I can think of is create a copy of above rule with STRING replaced by SCALE, but this is just one of the many similar rules which would need such fixing. Furthermore there are many other terminals which can get matched to STRING. So that means way too many rules!

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  • Retrieve position of a google maps v3 marker to Qt in a desktop app with QtWebKit

    - by nelas
    I'm building a Qt app with Python where you can point and click at a (google) map and get the coordinates of the location. The map is shown through a QWebView loading a simple HTML page and the user can create markers by clicking. Screenshot of the widget after clicking on the map: However, I'm having trouble to retrieve the just-clicked location coordinates back to Qt (so that I can use them as variables -- and, for example, show them in the QLineEdits on the topleft corner above, as current location of the marker). This is the relevant part of the HTML file: <script type="text/javascript"> var map; function initialize() { var local = new google.maps.LatLng(-23.4,-40.3); var myOptions = { zoom: 5, center: local, mapTypeId: google.maps.MapTypeId.ROADMAP } map = new google.maps.Map(document.getElementById("map_canvas"), myOptions); google.maps.event.addListener(map, 'rightclick', function(event) { placeMarker(event.latLng); }); } function placeMarker(location) { var clickedLocation = new google.maps.LatLng(location); var marker = new google.maps.Marker({ position: location, map: map }); map.setCenter(location); } function dummyTxt() { return 'This works.'; } </script> I've been trying with evaluateJavaScript, but was not able to retrieve the coordinates. I tried to created a function to access the position with marker.getPosition(), but with no luck. The dummy below works though.. newplace = QWebView.page().mainFrame().evaluateJavaScript(QString('dummyTxt()')) >>> print newplace.toString() This works. Any suggestions on how to get the coordinates back to Qt?

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  • trackPageView on Google Analytics for iPhone Not Working

    - by DigitalZombieKid
    I'm trying to get Google Analytics working on an iPhone application without much luck. I've followed all the instructions on their website (google/apis/analytics/docs/tracking/mobileAppsTracking.html) and studied their sample application (google/gaformobileapps/GoogleAnalyticsIphone_0.7.tar.gz). When I run my application and go to Google Analytics' website (https://www.google.com/analytics/reporting/), the only page that is recording is /app_entry_point. I'm seeing one count in my Google Analytics detailed report once every time my app fires up. However, I have added other pages to be tracked but it's not working. Here is a sample of two pages I've added to be tracked: trackPageview:@"/calculator"; trackPageview:@"/tellafriend"; I call them from various ViewControllers in the app. In each of those view controllers I import the the GANTracker header: #import "GANTracker.h" I'll admit it: I'm an objective-c newbie. Any help you can offer is greatly appreciated! Do I need to physically dispatch them to get the trackPageview working? If so, why is the /app_entry_point page the only page that is recorded by Google Analytics?

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  • web development using google sites

    - by CHID
    Hi, I have hosted a website. But now my client asks to change it to http://sites.google.com. They hav registered their domain in google. I logged in the site and saw the procedures to create a website from scratch. But is there any way to directly replace the site into google sites. Like, in my site i hav included css files in a folder called stylesheets/css and access it through the link tag. And there are several folders lik that, viz images, scripts etc. 1.Now if i have to transfer it to google sites, where do i create the folders and stuff. I have the priviliges to login to the admin part of the site. 2.And also is there anyway to create database and access it in google sites? 3.Also i see that only html pages can be created. Is there a way to add php pages or other scripting languages? 4.Going forward will google sites be usefull for professional web designing. pls give ideas on whether or not google sites is a good idea to go with

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  • Select box is not working properly after including google custom search box in web page

    - by Vinay
    I have got a select box and google custom search box in a page, when i choose a option from select box and navigate away from the page and again if i come back to the same page the option will not be selected (violates the default functionality of select box), The code is below <script src="https://www.google.com/jsapi" type="text/javascript"></script> <script type="text/javascript"> google.load('search', '1', {language : 'en'}); google.setOnLoadCallback(function() { var customSearchControl = new google.search.CustomSearchControl('004920913350056953771:kpkclvhujzk'); customSearchControl.setResultSetSize(google.search.Search.FILTERED_CSE_RESULTSET); var options = new google.search.DrawOptions(); options.setAutoComplete(true); options.enableSearchboxOnly("<?=$homeurl?>my_results.php", "query"); customSearchControl.draw('cse-search-form', options); }, true); </script> <select multiple="yes"> <option>1</option> <option>2</option> </select> If i remove the custom search script, the select box selected option will be retained even after navigating away from the page. (default functionality) Its working fine in chrome, IE but not in Firefox. Is there any solution for this, so that select box must work fine even in the presence of search box, but the order must be same 1) Search box 2)Select Box

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  • Benefits of 'Optimize code' option in Visual Studio build

    - by gt
    Much of our C# release code is built with the 'Optimize code' option turned off. I believe this is to allow code built in Release mode to be debugged more easily. Given that we are creating fairly simple desktop software which connects to backend Web Services, (ie. not a particularly processor-intensive application) then what if any sort of performance hit might be expected? And is any particular platform likely to be worse affected? Eg. multi-processor / 64 bit.

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  • When to use certain optimizations such as -fwhole-program and -fprofile-generate with several shared libraries

    - by James
    Probably a simple answer; I get quite confused with the language used in the GCC documentation for some of these flags! Anyway, I have three libraries and a programme which uses all these three. I compile each of my libraries seperately with individual (potentially) different sets of warning flags. However, I compile all three libraries with the same set of optimisation flags. I then compile my main programme linking in these three libraries with its own set of warning flags and the same optimisation flags used during the libraries' compilation. 1) Do I have to compile the libraries with optimisation flags present or can I just use these flags when compiling the final programme and linking to the libraries? If the latter, will it then optimise all or just some (presumably that which is called) of the code in these libraries? 2) I would like to use -fwhole-program -flto -fuse-linker-plugin and the linker plugin gold. At which stage do I compile with these on ... just the final compilation or do these flags need to be present during the compilation of the libraries? 3) Pretty much the same as 2) however with, -fprofile-generate -fprofile-arcs and -fprofile-use. I understand one first runs a programme with generate, and then with use. However, do I have to compile each of the libraries with generate/use etc. or just the final programme? And if it is just the last programme, when I then compeil with -fprofile-use will it also optimise the libraries functionality? Many thanks, James

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  • Delphi: All constants are constant, but some are more constant than others?

    - by Ian Boyd
    Consider: clHotlight: TColor = $00FF9933; clLink = clHotLight; //alias of clHotlight [Error] file.pas: Constant expression expected and the alternate wording that works: clHotlight = TColor($00FF9933); clLink = clHotLight; //alias of clHotlight Explain. Then consider: AdministratorGUID: TGUID = '{DE44EEA0-6712-11D4-ADD4-0006295717DA}'; SuperuserGUID = AdministratorGUID; //alias of AdministratorGUID [Error] file.pas: Constant expression expected And fix.

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  • Languages and VMs: Features that are hard to optimize and why

    - by mrjoltcola
    I'm doing a survey of features in preparation for a research project. Name a mainstream language or language feature that is hard to optimize, and why the feature is or isn't worth the price paid, or instead, just debunk my theories below with anecdotal evidence. Before anyone flags this as subjective, I am asking for specific examples of languages or features, and ideas for optimization of these features, or important features that I haven't considered. Also, any references to implementations that prove my theories right or wrong. Top on my list of hard to optimize features and my theories (some of my theories are untested and are based on thought experiments): 1) Runtime method overloading (aka multi-method dispatch or signature based dispatch). Is it hard to optimize when combined with features that allow runtime recompilation or method addition. Or is it just hard, anyway? Call site caching is a common optimization for many runtime systems, but multi-methods add additional complexity as well as making it less practical to inline methods. 2) Type morphing / variants (aka value based typing as opposed to variable based) Traditional optimizations simply cannot be applied when you don't know if the type of someting can change in a basic block. Combined with multi-methods, inlining must be done carefully if at all, and probably only for a given threshold of size of the callee. ie. it is easy to consider inlining simple property fetches (getters / setters) but inlining complex methods may result in code bloat. The other issue is I cannot just assign a variant to a register and JIT it to the native instructions because I have to carry around the type info, or every variable needs 2 registers instead of 1. On IA-32 this is inconvenient, even if improved with x64's extra registers. This is probably my favorite feature of dynamic languages, as it simplifies so many things from the programmer's perspective. 3) First class continuations - There are multiple ways to implement them, and I have done so in both of the most common approaches, one being stack copying and the other as implementing the runtime to use continuation passing style, cactus stacks, copy-on-write stack frames, and garbage collection. First class continuations have resource management issues, ie. we must save everything, in case the continuation is resumed, and I'm not aware if any languages support leaving a continuation with "intent" (ie. "I am not coming back here, so you may discard this copy of the world"). Having programmed in the threading model and the contination model, I know both can accomplish the same thing, but continuations' elegance imposes considerable complexity on the runtime and also may affect cache efficienty (locality of stack changes more with use of continuations and co-routines). The other issue is they just don't map to hardware. Optimizing continuations is optimizing for the less-common case, and as we know, the common case should be fast, and the less-common cases should be correct. 4) Pointer arithmetic and ability to mask pointers (storing in integers, etc.) Had to throw this in, but I could actually live without this quite easily. My feelings are that many of the high-level features, particularly in dynamic languages just don't map to hardware. Microprocessor implementations have billions of dollars of research behind the optimizations on the chip, yet the choice of language feature(s) may marginalize many of these features (features like caching, aliasing top of stack to register, instruction parallelism, return address buffers, loop buffers and branch prediction). Macro-applications of micro-features don't necessarily pan out like some developers like to think, and implementing many languages in a VM ends up mapping native ops into function calls (ie. the more dynamic a language is the more we must lookup/cache at runtime, nothing can be assumed, so our instruction mix is made up of a higher percentage of non-local branching than traditional, statically compiled code) and the only thing we can really JIT well is expression evaluation of non-dynamic types and operations on constant or immediate types. It is my gut feeling that bytecode virtual machines and JIT cores are perhaps not always justified for certain languages because of this. I welcome your answers.

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