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• I wired up a z 80 using telephone wire and put a jump to 0000 0000 0000 0000

  - by john

  I put 1100 0011 0000 0000 0000 0000 in the 2764 eprom --- this is supposed to test the z80 -- I have a 555 timer running at 500 khz. Can this small program work with the z80 ? I looked at the address pins on a m465 oscilloscope. The address shows highs up to 0100 0000. I think it should only count to 0000 0000 0000 0011. Can the z80 be tested? The Santa Clara Valley also made the lm1871 radio control chip that could not show a high or a low without completing the entire rc loop.

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• Is there a way to ignore Cache errors in Django?

  - by Josh Smeaton

  I've just set our development Django site to use redis for a cache backend and it was all working fine. I brought down redis to see what would happen, and sure enough Django 404's due to cache backend behaviour. Either the Connection was refused, or various other errors. Is there any way to instruct Django to ignore Cache errors, and continue processing the normal way? It seems weird that caching is a performance optimization, but can bring down an entire site if it fails. I tried to write a wrapper around the backend like so: class CacheClass(redis_backend.CacheClass): """ Wraps the desired Cache, and falls back to global_settings default on init failure """ def __init__(self, server, params): try: super(CacheClass, self).__init__(server, params) except Exception: from django.core import cache as _ _.cache = _.get_cache('locmem://') But that won't work, since I'm trying to set the cache type in the call that sets the cache type. It's all a very big mess. So, is there any easy way to swallow cache errors? Or to set the default cache backend on failure?

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• Apache2 on Ubuntu Server w/ CGI, FastCGI, mod_php

  - by illegal3alien

  I've looked at various websites on configuring Apache with cgi and can't get mod_fcgid to work. It works fine using mod_php5, but I wanted to compare performance using cgi and fastcgi. I tried methods using FGCIWrapper among various other techniques and the only one that didn't result in an unlogged 403 or download of the file was using "Action application/x-httpd-php /usr/bin/php-cgi" When trying to configure mod_fcgid the file normally just started a download of an unprocessed file. I used wget to check headers and type was "application/x-httpd-php" At one point I was able to get to the page, but it resulted in a 403, which was listed in access.log, but not error.log (I was told it should be in there too) I tried to get it working on a fresh install of Ubuntu Server 10.04 LTS and 10.10 and had the same results on both, so I'm not doing something correctly in terms of configuration. I tried virtualmin and could only get mod_php to work. The page just prompted a download when selecting cgi or fcgi from the control panel.

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• Is a selector like *+* safe to use?

  - by mcmullins

  I recently came across this CSS selector while trying to find a way to easily space out major blog elements such as paragraphs and images. An example of its use would be something like this: .post *+* {margin-top: 15px;} /* or... */ .post > *+* {margin-top: 15px;} /* if you don't want the margin to apply to nested elements */ At first glance, it seemed pretty useful. So my question is: What downsides are there to using these selectors? Specifically: What's the browser support like for this? Are there any cases you wouldn't want an even margin spacing between elements in an article and if not, is it easier to declare this first and then overwrite or simply declare each element individually? Does this have performance issues since you're selecting everything twice?

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• Giving Users an Option Between UDP & TCP?

  - by cam

  After studying TCP/UDP difference all week, I just can't decide which to use. I have to send a large amount of constant sensor data, while at the same time sending important data that can't be lost. This made a perfect split for me to use both, then I read a paper (http://www.isoc.org/INET97/proceedings/F3/F3_1.HTM) that says using both causes packet/performance loss in the other. Is there any issue presented if I allow the user to choose which protocol to use (if I program both server side) instead of choosing myself? Are there any disadvantages to this? The only other solution I came up with is to use UDP, and if there seems to be too great of loss of packets, switch to TCP (client-side).

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• Large static arrays are slowing down class load, need a better/faster lookup method

  - by Visualize

  I have a class with a couple static arrays: an int[] with 17,720 elements a string[] with 17,720 elements I noticed when I first access this class it takes almost 2 seconds to initialize, which causes a pause in the GUI that's accessing it. Specifically, it's a lookup for Unicode character names. The first array is an index into the second array. static readonly int[] NAME_INDEX = { 0x0000, 0x0001, 0x0005, 0x002C, 0x003B, ... static readonly string[] NAMES = { "Exclamation Mark", "Digit Three", "Semicolon", "Question Mark", ... The following code is how the arrays are used (given a character code). [Note: This code isn't a performance problem] int nameIndex = Array.BinarySearch<int>(NAME_INDEX, code); if (nameIndex > 0) { return NAMES[nameIndex]; } I guess I'm looking at other options on how to structure the data so that 1) The class is quickly loaded, and 2) I can quickly get the "name" for a given character code. Should I not be storing all these thousands of elements in static arrays?

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• [PHP] background upload

  - by Robijntje007

  I am working with a form that allows me to upload files via a local folder and FTP. So I want to move files over ftp (which already works) Because of performance reasons I chose this process to run in the background so I use nfcftpput (linux) In CLI the following command works perfectly: ncftpput-b-u name -p password -P 1980 127.0.0.1 /upload/ /home/Downloads/upload.zip (Knowing that the b-parameter triggers background process) But if I run it via PHP it does not work (without the-b parameter it does) PHP code: $cmd = "ncftpput -b -u name -p password -P 1980 127.0.0.1 /upload/ /home/Downloads/upload.zip"; $return = exec($cmd);

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• A non-blocking server with java.io

  - by Jon

  Everybody knows that java IO is blocking, and java NIO is non-blocking. In IO you will have to use the thread per client pattern, in NIO you can use one thread for all clients. Now my question follows: is it possible to make a non-blocking design using only the Java IO api. (not NIO) I was thinking about a pattern like this (obviously very simplified); List<Socket> li; for (Socket s : li) { InputStream in = s.getInputStream(); byte[] data = in.available(); in.read(data); // processData(data); (decoding packets, encoding outgoing packets } Also note that the client will always be ready for reading data. What are your opinions on this? Will this be suitable for a server that should at least hold a few hundred of clients without major performance issues?

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• Is it better to alloc/dealloc new UIBarButtonItems when toggling Edit/Done? Why?

  - by cambria

  Apple's documentation implies that for a UITableView editable with an "Edit/Done" button, you should create and destroy the button each time it's toggled. Here's a snippet of code "BonjourWeb" sample code project that does this: if (editing) { // Add the "done" button to the navigation bar UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(doneAction:)]; self.navigationItem.leftBarButtonItem = doneButton; [doneButton release]; [self addAddButton:YES]; } else { if ([self.customs count]) { // Add the "edit" button to the navigation bar UIBarButtonItem *editButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemEdit target:self action:@selector(editAction:)]; self.navigationItem.leftBarButtonItem = editButton; [editButton release]; } Is this really better than just editing the title of the button? Is there some performance optimisation that I'm not seeing? Or is this just bad example source?

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• How do I keep JTextFields in a Java Swing BoxLayout from expanding?

  - by Matthew

  I have a JPanel that looks something like this: JPanel panel = new JPanel(); panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS)); ... panel.add (jTextField1); panel.add (Box.createVerticalStrut(10)); panel.add (jButton1); panel.add (Box.createVerticalStrut(30)); panel.add (jTextField2); panel.add (Box.createVerticalStrut(10)); panel.add (jButton2); ... //etc. My problem is that the JTextFields become huge vertically. I want them to only be high enough for a single line, since that is all that the user can type in them. The buttons are fine (they don't expand vertically). Is there any way to keep the JTextFields from expanding? I'm pretty new to Swing, so let me know if I'm doing everything horribly wrong.

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• Layering of CSS with z-index

  - by Matt Hintzke

  I have a created a 3 circle venn diagram using pure CSS3 and each circle has a :hover event attached to it. I also have an image of an arrow which is pointing to the center of the venn diagram. I want the arrow to visually appear to be on top of the circles, so I put the z-index higher on the arrow than the circles. The problem now, is that the :hover event does not trigger on half of the venn diagram now because the arrow image is on top, which causes the hover to be on top of the arrow rather than the circle that I want it to be over. So is it possible to make an element have a high z-index visually but not programmatically?

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• Using locks inside a loop

  - by Xaqron

  // Member Variable private readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile shared int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• How to create an ARGB_8888 pixel value?

  - by vidstige

  Say I want to create an array of pixel values to pass into the createBitmap method described here. I have three int values r, g, b in the range 0 - 0xff. How do I transform those into a opaque pixel p? Does the alpha channel go in the high byte or the low byte? I googled up the documentation but it only states that: Each pixel is stored on 4 bytes. Each channel (RGB and alpha for translucency) is stored with 8 bits of precision (256 possible values.) This configuration is very flexible and offers the best quality. It should be used whenever possible. So, how to write this method? int createPixel(int r, int g, int b) { retrurn ? }

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• How to Get the Method/Function Call Trace for a Specific Run?

  - by JackWM

  Given a Java or JavaScript program, after its execution, print out a sequence of calls. The calls are in invocation order. E.g. main() { A(); } A() { B(); C(); } Then the call trace should be: main -> A() -> B() -> C() Is there any tool that can profile and output this kind of information? It seems this is common a need for debugging or performance tuning. I noticed that some profilers can do this, but I prefer a simpler/easy-to-use one. Thanks!

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• Switching from C++ (with a lot of STL use) to C for interpreter building

  - by wndsr

  I'm switching from C++ to C because I'm rebuilding my toy interpreter. I was used to vectors for dynamic allocation of objects like tokens or instructions of my programs, stacks and mainly strings with all their aspects. Now, in C I'm not going to have all these anymore. I know that I will have to use a lot of memory management, too. I'm completely new to C, I only know the high-level easy-life data structures from the STL, how can I get started with strings and dynamic memory allocation?

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• How can I implement lazy loading on a page with 500+ images?

  - by Fedor

  I basically have a booking engine unit results page which must show 40 units and per each unit there's 1 large image of the first thumbnail and an X number of accompanying thumbnail images. I've been using the jquery lazy load plugin, but it's not thorough enough ( I'm invoking it on DOM Ready ), plus it doesn't really work in IE ( 50% of the clients use IE so it's a big issue ). What I think I really need to do is not really spit out the image but a fake element such as a span, and possibly modify my code such that if the user views the span, render it into an image element. <span src="/images/foo.gif"> The booking engine relies on JS so I think I might be forced to just rely on ajaxifying all the thumbnails and have event handlers on window scroll, etc in order for the page to be "usable" and load at an average time ( 2-3 seconds instead of 5-30s on high speed DSL/Cable ). I'd appreciate any examples or ideas.

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• misleading plot issue in mathematica

  - by Qiang Li

  I want to study some "strange" functions by plotting them out in mathematica. One example is the following: mod2[x_] := Which[Mod[x, 2] >= 1, -2 + Mod[x, 2], True, Mod[x, 2]]; f[x_] := Which[-1 <= x <= 1, Abs[x], True, Abs[mod2[x]]]; fn[x_, n_] := Sum[(3/4)^i*f[4^n*x], {i, 0, n}] Plot[{fn[x, 0], fn[x, 1], fn[x, 2], fn[x, 5]}, {x, -2, 2}] However, the plot I got from mma is misleading, in the sense that the maxima and minima of fn[x, 5] should be on the same two levels. But due to high oscillation of the function, and the fact that clearly mma only takes limited number of points to draw the function, you see the plot exhibit strange behavior. Is there any option in plot to remedy for this? Many thanks.

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• Does Oracle 11g automatically index fields frequently used for full table scans?

  - by gustafc

  I have an app using an Oracle 11g database. I have a fairly large table (~50k rows) which I query thus: SELECT omg, ponies FROM table WHERE x = 4 Field x was not indexed, I discovered. This query happens a lot, but the thing is that the performance wasn't too bad. Adding an index on x did make the queries approximately twice as fast, which is far less than I expected. On, say, MySQL, it would've made the query ten times faster, at the very least. I'm suspecting Oracle adds some kind of automatic index when it detects that I query a non-indexed field often. Am I correct? I can find nothing even implying this in the docs.

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• Question About Eclipse Java Debugger Conditional Breakpoints Inefficiency

  - by Personman

  I just set a conditional breakpoint in Eclipse's debugger with a mildly inefficient condition by breakpoint standards - checking whether a HashMap's value list (8 elements) contains Double.NaN. This resulted in an extremely noticeable slowdown in performance - after about five minutes, I gave up. Then I copy pasted the condition into an if statement at the exact same line, put a noop in the if, and set a normal breakpoint there. That breakpoint was reached in the expected 20-30 seconds. Is there something special that conditional breakpoints do that is different from this, or is Eclipse's implementation just kinda stupid? It seems like they could fairly easily just do exactly the same thing behind the scenes.

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• Codeigniter - Is it ok to add functionality to the constructor in controllers?

  - by Irro

  I'm making a project where I want the user to search for shops in different cities and would like the url to be like this: domain/shop/city/name. So I created a controller in codeigniter called Shop. But I cant create a city function since the city part of the url changes dependent on city name. One easy way to do it would be to add a function called "search" and add the functionality there but then I get url's like: domain/shop/search/city/name which I really would like to avoid. So my question is if it's ok to add my functionality directly into the constructor to avoid that extra "search" part in the url? I'm afraid that there might be some performance tricks involved that potentially keeps the class in memory so the constructor will not be called every time.

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• Declaring variables for limited scope at the head of the for loop

  - by Helper Method

  In Java, you sometimes do something like this: for (int a = 1, b = 2; b < high;) { if (b % 2 == 0) { result += b; } int tmp = b; b = a + b; a = tmp; } Here, I used a for loop instead of a while loop to limit the scope of a and b. But how can I achieve this in JavaFX? The for loop doesn't seem to offer this possibility. Do I have to use a while loop?

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• How to get REALLY fast python over a simple loop

  - by totallymike

  I'm working on a spoj problem, INTEST. The goal is to specify the number of test cases (n) and a divisor (k), then feed your program n numbers. The program will accept each number on a newline of stdin and after receiving the nth number, will tell you how many were divisible by k. The only challenge in this problem is getting your code to be FAST because it k can be anything up to 10^7 and the test cases can be as high as 10^9. I'm trying to write it in python and having trouble speeding it up. Any ideas? import sys first_in = raw_input() thing = first_in.split() n = int(thing[0]) k = int(thing[1]) total = 0 i = 0 for line in sys.stdin: t = int(line) if t % k == 0: total += 1 print total

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• When is BIG, big enough for a database?

  - by David ???

  I'm developing a Java application that has performance at its core. I have a list of some 40,000 "final" objects, i.e., I have an initialization input data of 40,000 vectors. This data is unchanged throughout the program's run. I am always preforming lookups against a single ID property to retrieve the proper vectors. Currently I am using a HashMap over a sub-sample of a 1,000 vectors, but I'm not sure it will scale to production. When is BIG, actually big enough for a use of DB? One more thing, an SQLite DB is a viable option as no concurrency is involved, so I guess the "threshold" for db use, is perhaps lower.

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• cross domain gwt ?

  - by jlo

  is there a way to run gwt on a proxy loaded web page ? ex) using proxy script on myexamplesite.com that loads finance.google.com, and running GWT on the newly loaded page. I've been doing the above before I found about GWT, using LAMP stack + Jquery (UI), which quickly turned out to be crap and inefficient. All this trouble to bypass browser's default Single Origin Policy. So, right now, is it possible to overcome this problem with GWT ? Is it possible to some how, run javascript on a html page from finance.google.com loaded into myexamplesite.com's frame with GWT or other solution? I am not looking to do JSON or RSS related topics. What I need is high lighted in bold. Is GWT + Gears what I should be using ? Thank you.

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• Microphone input

  - by George

  I'm trying to build a gadget that detects pistol shots using Android. It's a part of a training aid for pistol shooters that tells how the shots are distributed in time and I use a HTC Tattoo for testing. I use the MediaRecorder and its getMaxAmplitude method to get the highest amplitude during the last 1/100 s but it does not work as expected; speech gives me values from getMaxAmplitude in the range from 0 to about 25000 while the pistol shots (or shouting!) only reaches about 15000. With a sampling frequency of 8kHz there should be some samples with considerably high level. Anyone who knows how these things work? Are there filters that are applied before registering the max amplitude. If so, is it hardware or software? Thanks, /George

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