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  • Process is killed without a (obvious) reason and program stops working

    - by Krzysiek Gurniak
    Here's what my program is supposed to do: create 4 child processes: process 0 is reading 1 byte at a time from STDIN, then writing it into FIFO process 1 is reading this 1 byte from fifo and write its value as HEX into shared memory process 2 is reading HEX value from shared memory and writing it into pipe finally process 3 is reading from pipe and writing into STDOUT (in my case: terminal) I can't change communication channels. FIFO, then shared memory, then pipes are the only option. My problem: Program stops at random moments when some file is directed into stdin (for example:./program < /dev/urandom). Sometimes after writing 5 HEX values, sometimes after 100. Weird thing is that when it is working and in another terminal I write "pstree -c" there is 1 main process with 4 children processes (which is what I want), but when I write "pstree -c" after it stopped writing (but still runs) there are only 3 child processes. For some reason 1 is gone even though they all have while(1) in them.. I think I might have problem with synchronization here, but I am unable to spot it (I've tried for many hours). Here's the code: #include <unistd.h> #include <fcntl.h> #include <stdio.h> #include <string.h> #include <stdlib.h> #include <sys/shm.h> #include <sys/sem.h> #include <sys/types.h> #include <sys/wait.h> #include <sys/stat.h> #include <string.h> #include <signal.h> #define BUFSIZE 1 #define R 0 #define W 1 // processes ID pid_t p0, p1, p2, p3; // FIFO variables int fifo_fd; unsigned char bufor[BUFSIZE] = {}; unsigned char bufor1[BUFSIZE] = {}; // Shared memory variables key_t key; int shmid; char * tab; // zmienne do pipes int file_des[2]; char bufor_pipe[BUFSIZE*30] = {}; void proces0() { ssize_t n; while(1) { fifo_fd = open("/tmp/fifo",O_WRONLY); if(fifo_fd == -1) { perror("blad przy otwieraniu kolejki FIFO w p0\n"); exit(1); } n = read(STDIN_FILENO, bufor, BUFSIZE); if(n<0) { perror("read error w p0\n"); exit(1); } if(n > 0) { if(write(fifo_fd, bufor, n) != n) { perror("blad zapisu do kolejki fifo w p0\n"); exit(1); } memset(bufor, 0, n); // czyszczenie bufora } close(fifo_fd); } } void proces1() { ssize_t m, x; char wartosc_hex[30] = {}; while(1) { if(tab[0] == 0) { fifo_fd = open("/tmp/fifo", O_RDONLY); // otwiera plik typu fifo do odczytu if(fifo_fd == -1) { perror("blad przy otwieraniu kolejki FIFO w p1\n"); exit(1); } m = read(fifo_fd, bufor1, BUFSIZE); x = m; if(x < 0) { perror("read error p1\n"); exit(1); } if(x > 0) { // Konwersja na HEX if(bufor1[0] < 16) { if(bufor1[0] == 10) // gdy enter { sprintf(wartosc_hex, "0x0%X\n", bufor1[0]); } else { sprintf(wartosc_hex, "0x0%X ", bufor1[0]); } } else { sprintf(wartosc_hex, "0x%X ", bufor1[0]); } // poczekaj az pamiec bedzie pusta (gotowa do zapisu) strcpy(&tab[0], wartosc_hex); memset(bufor1, 0, sizeof(bufor1)); // czyszczenie bufora memset(wartosc_hex, 0, sizeof(wartosc_hex)); // przygotowanie tablicy na zapis wartosci hex x = 0; } close(fifo_fd); } } } void proces2() { close(file_des[0]); // zablokuj kanal do odczytu while(1) { if(tab[0] != 0) { if(write(file_des[1], tab, strlen(tab)) != strlen(tab)) { perror("blad write w p2"); exit(1); } // wyczysc pamiec dzielona by przyjac kolejny bajt memset(tab, 0, sizeof(tab)); } } } void proces3() { ssize_t n; close(file_des[1]); // zablokuj kanal do zapisu while(1) { if(tab[0] == 0) { if((n = read(file_des[0], bufor_pipe, sizeof(bufor_pipe))) > 0) { if(write(STDOUT_FILENO, bufor_pipe, n) != n) { perror("write error w proces3()"); exit(1); } memset(bufor_pipe, 0, sizeof(bufor_pipe)); } } } } int main(void) { key = 5678; int status; // Tworzenie plikow przechowujacych ID procesow int des_pid[2] = {}; char bufor_proces[50] = {}; mknod("pid0", S_IFREG | 0777, 0); mknod("pid1", S_IFREG | 0777, 0); mknod("pid2", S_IFREG | 0777, 0); mknod("pid3", S_IFREG | 0777, 0); // Tworzenie semaforow key_t klucz; klucz = ftok(".", 'a'); // na podstawie pliku i pojedynczego znaku id wyznacza klucz semafora if(klucz == -1) { perror("blad wyznaczania klucza semafora"); exit(1); } semafor = semget(klucz, 1, IPC_CREAT | 0777); // tworzy na podstawie klucza semafor. 1 - ilosc semaforow if(semafor == -1) { perror("blad przy tworzeniu semafora"); exit(1); } if(semctl(semafor, 0, SETVAL, 0) == -1) // ustawia poczatkowa wartosc semafora (klucz, numer w zbiorze od 0, polecenie, argument 0/1/2) { perror("blad przy ustawianiu wartosci poczatkowej semafora"); exit(1); } // Tworzenie lacza nazwanego FIFO if(access("/tmp/fifo", F_OK) == -1) // sprawdza czy plik istnieje, jesli nie - tworzy go { if(mkfifo("/tmp/fifo", 0777) != 0) { perror("blad tworzenia FIFO w main"); exit(1); } } // Tworzenie pamieci dzielonej // Lista pamieci wspoldzielonych, komenda "ipcs" // usuwanie pamieci wspoldzielonej, komenta "ipcrm -m ID_PAMIECI" shmid = shmget(key, (BUFSIZE*30), 0666 | IPC_CREAT); if(shmid == -1) { perror("shmget"); exit(1); } tab = (char *) shmat(shmid, NULL, 0); if(tab == (char *)(-1)) { perror("shmat"); exit(1); } memset(tab, 0, (BUFSIZE*30)); // Tworzenie lacza nienazwanego pipe if(pipe(file_des) == -1) { perror("pipe"); exit(1); } // Tworzenie procesow potomnych if(!(p0 = fork())) { des_pid[W] = open("pid0", O_WRONLY | O_TRUNC | O_CREAT); // 1 - zapis, 0 - odczyt sprintf(bufor_proces, "Proces0 ma ID: %d\n", getpid()); if(write(des_pid[W], bufor_proces, sizeof(bufor_proces)) != sizeof(bufor_proces)) { perror("blad przy zapisie pid do pliku w p0"); exit(1); } close(des_pid[W]); proces0(); } else if(p0 == -1) { perror("blad przy p0 fork w main"); exit(1); } else { if(!(p1 = fork())) { des_pid[W] = open("pid1", O_WRONLY | O_TRUNC | O_CREAT); // 1 - zapis, 0 - odczyt sprintf(bufor_proces, "Proces1 ma ID: %d\n", getpid()); if(write(des_pid[W], bufor_proces, sizeof(bufor_proces)) != sizeof(bufor_proces)) { perror("blad przy zapisie pid do pliku w p1"); exit(1); } close(des_pid[W]); proces1(); } else if(p1 == -1) { perror("blad przy p1 fork w main"); exit(1); } else { if(!(p2 = fork())) { des_pid[W] = open("pid2", O_WRONLY | O_TRUNC | O_CREAT); // 1 - zapis, 0 - odczyt sprintf(bufor_proces, "Proces2 ma ID: %d\n", getpid()); if(write(des_pid[W], bufor_proces, sizeof(bufor_proces)) != sizeof(bufor_proces)) { perror("blad przy zapisie pid do pliku w p2"); exit(1); } close(des_pid[W]); proces2(); } else if(p2 == -1) { perror("blad przy p2 fork w main"); exit(1); } else { if(!(p3 = fork())) { des_pid[W] = open("pid3", O_WRONLY | O_TRUNC | O_CREAT); // 1 - zapis, 0 - odczyt sprintf(bufor_proces, "Proces3 ma ID: %d\n", getpid()); if(write(des_pid[W], bufor_proces, sizeof(bufor_proces)) != sizeof(bufor_proces)) { perror("blad przy zapisie pid do pliku w p3"); exit(1); } close(des_pid[W]); proces3(); } else if(p3 == -1) { perror("blad przy p3 fork w main"); exit(1); } else { // proces macierzysty waitpid(p0, &status, 0); waitpid(p1, &status, 0); waitpid(p2, &status, 0); waitpid(p3, &status, 0); //wait(NULL); unlink("/tmp/fifo"); shmdt(tab); // odlaczenie pamieci dzielonej shmctl(shmid, IPC_RMID, NULL); // usuwanie pamieci wspoldzielonej printf("\nKONIEC PROGRAMU\n"); } } } } exit(0); }

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  • Memory mapping of files and system cache behavior in WinXP

    - by Canopus
    Our application is memory intensive and deals with reading a large number of disk files. The total load can be more than 3 GB. There is a custom memory manager that uses memory mapped files to achieve reading of such a huge data. The files are mapped into the process memory space only when needed and with this the process memory is well under control. But what is observed is, with memory mapping, the system cache keeps on increasing until it occupies the available physical memory. This leads to the slowing down of the entire system. My question is how to prevent system cache from hogging the physical memory? I attempted to remove the file buffering (by using FILE_FLAG_NO_BUFFERING ), but with this, the read operations take considerable amount of time and slows down the application performance. How to achieve the scalability without sacrificing much on performance. What are the common techniques used in such cases? I dont have a good understanding of the WinXP OS caching behavior. Any good links explaining the same would also be helpful.

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  • std::ifstream buffer caching

    - by ledokol
    Hello everybody, In my application I'm trying to merge sorted files (keeping them sorted of course), so I have to iterate through each element in both files to write the minimal to the third one. This works pretty much slow on big files, as far as I don't see any other choice (the iteration has to be done) I'm trying to optimize file loading. I can use some amount of RAM, which I can use for buffering. I mean instead of reading 4 bytes from both files every time I can read once something like 100Mb and work with that buffer after that, until there will be no element in buffer, then I'll refill the buffer again. But I guess ifstream is already doing that, will it give me more performance and is there any reason? If fstream does, maybe I can change size of that buffer? added My current code looks like that (pseudocode) // this is done in loop int i1 = input1.read_integer(); int i2 = input2.read_integer(); if (!input1.eof() && !input2.eof()) { if (i1 < i2) { output.write(i1); input2.seek_back(sizeof(int)); } else input1.seek_back(sizeof(int)); output.write(i2); } } else { if (input1.eof()) output.write(i2); else if (input2.eof()) output.write(i1); } What I don't like here is seek_back - I have to seek back to previous position as there is no way to peek 4 bytes too much reading from file if one of the streams is in EOF it still continues to check that stream instead of putting contents of another stream directly to output, but this is not a big issue, because chunk sizes are almost always equal. Can you suggest improvement for that? Thanks.

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  • Howto open a file and remove the last line?

    - by sologhost
    I am looking to open up a file, grab the last line in the file where the line = "?", which is the closing tag for a php document. Than I am wanting to append data into it and add back in the "?" to the very last line. I've been trying a few approaches, but I'm not having any luck. Here's what I got so far, as I am reading from a zip file. Though I know this is all wrong, just needing some help with this please... // Open for reading is all we can do with zips and is all we need. if (zip_entry_open($zipOpen, $zipFile, "r")) { $fstream = zip_entry_read($zipFile, zip_entry_filesize($zipFile)); $fp = fopen($curr_lang_file, 'r+b'); while (!feof($fp)) { $output = fgets($fp, 16384); if (trim($output) == '?>') break; fwrite($fp, $output); } fclose($fp); file_put_contents($curr_lang_file, $fstream, FILE_APPEND); } $curr_lang_file is a filepath string to the actual file that needs to have the fstream appended to it, but after we remove the last line that equals '?'

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  • Casting pointer to object to void * in C++

    - by JB
    I've been reading StackOverflow too much and started doubting all the code I've ever written, I keep thinking "Is that undefined behavour?" even in code that has been working for ages. So my question - Is it safe and well defined behavour to cast a pointer to an object (In this case abstract interface classes) to a void* and then later on cast them back to the original class and call method using them? I'm fully aware that the code that does this is probably awful. I wouldn't even consider writing it like this now (this is old code which I don't really want to change), so I'm not looking for a discussion of better ways to do this. I already know how to write it better if I ever did this again. But if it's actually broken to rely on this in C++ then I'll have to look at changing the code, if it's merely awful code then changing it won't be a priority. I would have had no doubts about something this simple a year or two ago but as my understanding of C++ increases I actually find I have more and more worries about code being safe under the standards even if it works perfectly well. Perhaps reading too much stack overflow is a bad thing for productivity sometimes :P

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  • RIA Service - without database?

    - by Heko
    Helo! I need to write a RIA service to call Java webservices from Silverlight 3.0 app. I'm testing how stuff works and in my Web app I have a MyData class which has 2 properties (int ID, string Text): namespace SilverlightApplication1.Web { public class MyData { [Key] public int ID { get; set; } public string Text { get; set; } } } Then I wrote simple DomainService: [EnableClientAccess()] public class MyService : DomainService { public IQueryable<MyData> GetMyData(string Url) { // here I will call my WebService List<MyData> result = new List<MyData>(); result.Add(new MyData { ID = 1, Text = Url }); return result.AsQueryable(); } } } How can I get data into my SL app? Now I have this: namespace SilverlightApplication1 { public partial class MainPage : UserControl { public MainPage() { InitializeComponent(); MyContext context = new MyContext(); } } } I called and load but nothink worsk (exceptions, or nulls)... I had Invoke annotation but MyData is not TEntity and I can't use Strings or other simple types as well... :/ I'm reading and reading posts and nothing works like it should.. Any help would be really appreciated. Thank you!

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  • Why should I abstract my data layer?

    - by Gazillion
    OOP principles were difficult for me to grasp because for some reason I could never apply them to web development. As I developed more and more projects I started understanding how some parts of my code could use certain design patterns to make them easier to read, reuse, and maintain so I started to use it more and more. The one thing I still can't quite comprehend is why I should abstract my data layer. Basically if I need to print a list of items stored in my DB to the browser I do something along the lines of: $sql = 'SELECT * FROM table WHERE type = "type1"';' $result = mysql_query($sql); while($row = mysql_fetch_assoc($result)) { echo '<li>'.$row['name'].'</li>'; } I'm reading all these How-Tos or articles preaching about the greatness of PDO but I don't understand why. I don't seem to be saving any LoCs and I don't see how it would be more reusable because all the functions that I call above just seem to be encapsulated in a class but do the exact same thing. The only advantage I'm seeing to PDO are prepared statements. I'm not saying data abstraction is a bad thing, I'm asking these questions because I'm trying to design my current classes correctly and they need to connect to a DB so I figured I'd do this the right way. Maybe I'm just reading bad articles on the subject :) I would really appreciate any advice, links, or concrete real-life examples on the subject!

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  • Python 2.6 does not like appending to existing archives in zip files

    - by user313661
    Hello, In some Python unit tests of a program I'm working on we use in-memory zipfiles for end to end tests. In SetUp() we create a simple zip file, but in some tests we want to overwrite some archives. For this we do "zip.writestr(archive_name, zip.read(archive_name) + new_content)". Something like import zipfile from StringIO import StringIO def Foo(): zfile = StringIO() zip = zipfile.ZipFile(zfile, 'a') zip.writestr( "foo", "foo content") zip.writestr( "bar", "bar content") zip.writestr( "foo", zip.read("foo") + "some more foo content") print zip.read("bar") Foo() The problem is that this works fine in Python 2.4 and 2.5, but not 2.6. In Python 2.6 this fails on the print line with "BadZipfile: File name in directory "bar" and header "foo" differ." It seems that it is reading the correct file bar, but that it thinks it should be reading foo instead. I'm at a loss. What am I doing wrong? Is this not supported? I tried searching the web but could find no mention of similar problems. I read the zipfile documentation, but could not find anything (that I thought was) relevant, especially since I'm calling read() with the filename string. Any ideas? Thank you in advance!

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  • How to repair Java in Ubuntu after trying to switch to Java 6 using update-java-alternatives

    - by Kau-Boy
    I tried to switch from Java 5 to Java 6 using the "update-java-alternatives" command like explained on this page: https://help.ubuntu.com/community/Java But afterwards I get the following error when I tried to execute java: root@webserver:~# java Error occurred during initialization of VM Could not reserve enough space for object heap Could not create the Java virtual machine. I also tried to reinstall the java binaries using "apt-get" but I didn't succeed reinstalling it. I would like to post the "apt-get" errors, but unfortunately I don't know how to print out the error messages in English and not in German. My system is a Ubuntu 8.04 ROOT server. Here is the (Google translated) english text tring to install Java 6 again: root@server:~# apt-get install sun-java6-jdk Reading package lists ... Ready Dependency tree Reading state information ... Ready sun-java6-jdk is already the newest version. sun-java6-jdk set to manually installed. 0 upgraded, 0 newly installed, 0 to remove and 86 not upgraded. 1 not fully installed or removed. After this operation, 0B of additional disk space will be used. Set up a sun-java6-bin (6-03-0ubuntu2) ... Could not create the Java virtual machine. dpkg: error processing sun-java6-bin (- configure): Subprocess post-installation script returned error exit status 1 Errors were encountered while processing: sun-java6-bin E: Sub-process / usr / bin / dpkg returned an error code (1) I hope that this might help you helping me.

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  • Recover lost code from compiled apk

    - by AlexRamallo
    I have an issue here..and its making me really nervous. I was working on this game, and it was going great, so I took a copy of it on my laptop to work do some work while away from my computer. long story short, hard-drive failure + poor back ups led to me losing a very important class. Is there a way to decompile the apk to retrieve the bit of code that was lost? It isn't overly complicated or sophisticated, its just that its impossible to re-write it without reading every. single. line. of. code. in the entire application since it initializes a LOT of classes and loads a bunch of stuff in a specific way. With a quick google search I was able to find apktool, which decompiles it into a bunch of .smali files, which I don't think were designed for human reading. All I need to recover is one very big method in the class. I found the smali file that contains it and I think I found the line where it starts. something like .method public declared-synchronized load(Lcom/X/X/game/X;)I Anyone help would be appreciated since I would have to scrap the entire game without this method.

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  • File write not getting updated in Qt 4.5.3

    - by user249490
    Hi, I have an XML file. My application requires manipulation into that XML file. I will be writing the values into the XML value. I also have interface to display the read contents of the file. The user might add values into that XML (through an interface). Without closing the application he may decide to display the File contents also. Now the problem is, after i write the XML contents into the file, when i view the file through the interface , the values are not getting updated. After i close the application and open it the updated values are available.I am using the following code to achieve this. For writing QXmlStreamWriter and for reading QDomDocument, QDomNodeList. After i complete the writing, I flush and close the file too. lFile.flush(); lFile.close(); After reading also i closed the file. Can someone tell me what am doing wrong??

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  • How to read/write from erlang to a named pipe ?

    - by cstar
    I need my erlang application to read and write through a named pipe. Opening the named pipe as a file will fail with eisdir. I wrote the following module, but it is fragile and feels wrong in many ways. Also it fails on reading after a while. Is there a way to make it more ... elegant ? -module(port_forwarder). -export([start/2, forwarder/2]). -include("logger.hrl"). start(From, To)-> spawn(fun() -> forwarder(From, To) end). forwarder(FromFile, ToFile) -> To = open_port({spawn,"/bin/cat > " ++ ToFifo}, [binary, out, eof,{packet, 4}]), From = open_port({spawn,"/bin/cat " ++ FromFifo}, [binary, in, eof, {packet, 4}]), forwarder(From, To, nil). forwarder(From, To, Pid) -> receive {Manager, {command, Bin}} -> ?ERROR("Sending : ~p", [Bin]), To ! {self(), {command, Bin}}, forwarder(From, To, Manager); {From ,{data,Data}} -> Pid ! {self(), {data, Data}}, forwarder(From, To, Pid); E -> ?ERROR("Quitting, first message not understood : ~p", [E]) end. As you may have noticed, it's mimicking the port format in what it accepts or returns. I want it to replace a C code that will be reading the other ends of the pipes and being launched from the debugger.

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  • Sorting a very large text file in Java

    - by Alice
    Hi, I have a large text file I need to sort in Java. The format is: word [tab] frequency [new line] The algorithm for sorting is: Read some of the file, filtering for purlely alphabetic words. Once you have X number of alphabetic words, call Collections.sort and write the result to a file. Repeat until you have finished reading the file. Start reading two sorted files, comparing line by line for the word with higher frequency, and writing at the same time to a new file as to not load much into your memory Repeat until all files are merged into one large file Right now I've divided the large file into smaller ones (sorted by descending frequency) with 10,000 lines each. I know I need to somehow merge these files back together, but I'm not sure how to go about this. I've created a LinkedList to keep track of all the files created. The algorithm says to compare each line in the two files, except I've tried a case where , say file1 = 8,6,5,3,1 and file2 = 9,8,8,8,8. Then if I compare them line by line I would get file3 = 9,8,8,6,8,5,8,3,8,1 which is incorrectly sorted (they should be in decreasing order). I think I'm misunderstanding some part of the algorithm. If someone could point out what I should do instead, I'd greatly appreciate it. Thanks. edit: Yes this is an assignment. We aren't allowed to increase memory unfortunately :(

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  • How to open a file and remove the last line?

    - by sologhost
    I am looking to open up a file, grab the last line in the file where the line = "?", which is the closing tag for a php document. Than I am wanting to append data into it and add back in the "?" to the very last line. I've been trying a few approaches, but I'm not having any luck. Here's what I got so far, as I am reading from a zip file. Though I know this is all wrong, just needing some help with this please... // Open for reading is all we can do with zips and is all we need. if (zip_entry_open($zipOpen, $zipFile, "r")) { $fstream = zip_entry_read($zipFile, zip_entry_filesize($zipFile)); $fp = fopen($curr_lang_file, 'r+b'); while (!feof($fp)) { $output = fgets($fp, 16384); if (trim($output) == '?>') break; fwrite($fp, $output); } fclose($fp); file_put_contents($curr_lang_file, $fstream, FILE_APPEND); } $curr_lang_file is a filepath string to the actual file that needs to have the fstream appended to it, but after we remove the last line that equals '?'

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  • OS-independent Inter-program communication between Python and C

    - by Gyppo
    I have very little idea what I'm doing here, I've never done anything like this before, but a friend and I are writing competing chess programs and they need to be able to communicate to each other. He'll be writing mainly in C, the bulk of mine will be in Python, and I can see a few options: Alternately write to a temp file, or successive temp files. As the communication won't be in any way bulky this could work, but seems like an ugly work-around to me, the programs will have to keep checking for change/new files, it just seems ugly. Find some way of manipulating pipes i.e. mine.py| ./his . This seems like a bit of a dead end. Use sockets. But I don't know what I'd be doing, so could someone give me a pointer to some reading material? I'm not sure if there are OS-independent, language independent methods. Would there have to be some kind of supervisor server program to administrate? Use some kind of HTML protocol, which seems like overkill. I don't mind the programs having to run on the same machine. What do people recommend, and where can I start reading?

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  • Downloading Large JSON File to local file using Java

    - by user1279675
    I'm attempting to download a JSON from the following URL - http://api.crunchbase.com/v/1/companies.js - to a local file. I'm using Java 1.7 and the following JSON Libraries - http://www.json.org/java/ - to attempt to make it work. Here's my code: public static void download(String address, String localFileName) { OutputStream out = null; URLConnection conn = null; InputStream in = null; try { URL url = new URL(address); out = new BufferedOutputStream( new FileOutputStream(localFileName)); conn = url.openConnection(); in = conn.getInputStream(); byte[] buffer = new byte[1024]; int numRead; long numWritten = 0; while ((numRead = in.read(buffer)) != -1) { out.write(buffer, 0, numRead); numWritten += numRead; System.out.println(buffer.length); System.out.println(" " + buffer.hashCode()); } System.out.println(localFileName + "\t" + numWritten); } catch (Exception exception) { exception.printStackTrace(); } finally { try { if (in != null) { in.close(); } if (out != null) { out.close(); } } catch (IOException ioe) { } } } When I run the code everything seems to work until midway through the loop the program seems to stop and not continue reading the JSON Object. Does anyone know why this would stop reading? How could I fix the issue?

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  • Should programmers use boolean variables to "document" their code?

    - by froadie
    I'm reading McConell's Code Complete, and he discusses using boolean variables to document your code. For example, instead of: if((elementIndex < 0) || (MAX_ELEMENTS < elementIndex) || (elementIndex == lastElementIndex)){ ... } He suggests: finished = ((elementIndex < 0) || (MAX_ELEMENTS < elementIndex)); repeatedEntry = (elementIndex == lastElementIndex); if(finished || repeatedEntry){ ... } This strikes me as logical, good practice, and very self-documenting. However, I'm hesitant to start using this technique regularly as I've almost never come across it; and perhaps it would be confusing just by virtue of being rare. However, my experience is not very vast yet, so I'm interested in hearing programmers' opinion of this technique, and I'd be curious to know if anyone uses this technique regularly or has seen it often when reading code. Is this a worthwhile convention/style/technique to adopt? Will other programmers understand and appreciate it, or consider it strange?

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  • Sending Images over Sockets in C

    - by Takkun
    I'm trying to send an image file through a TCP socket in C, but the image isn't being reassembled correctly on the server side. I was wondering if anyone can point out the mistake? I know that the server is receiving the correct file size and it constructs a file of that size, but it isn't an image file. Client //Get Picture Size printf("Getting Picture Size\n"); FILE *picture; picture = fopen(argv[1], "r"); int size; fseek(picture, 0, SEEK_END); size = ftell(picture); //Send Picture Size printf("Sending Picture Size\n"); write(sock, &size, sizeof(size)); //Send Picture as Byte Array printf("Sending Picture as Byte Array\n"); char send_buffer[size]; while(!feof(picture)) { fread(send_buffer, 1, sizeof(send_buffer), picture); write(sock, send_buffer, sizeof(send_buffer)); bzero(send_buffer, sizeof(send_buffer)); } Server //Read Picture Size printf("Reading Picture Size\n"); int size; read(new_sock, &size, sizeof(1)); //Read Picture Byte Array printf("Reading Picture Byte Array\n"); char p_array[size]; read(new_sock, p_array, size); //Convert it Back into Picture printf("Converting Byte Array to Picture\n"); FILE *image; image = fopen("c1.png", "w"); fwrite(p_array, 1, sizeof(p_array), image); fclose(image);

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  • [C]Dynamic allocation memory of structure, related to GTK

    - by MakeItWork
    Hello, I have following structure: typedef struct { GtkWidget* PoziomaLinijka; GtkWidget* PionowaLinijka; GtkWidget* Label1; GtkWidget* Label2; gint x,y; } StrukturaDrawing; And i need to allocate it on the heap because later I have functions which uses that structure and I don't want to use global variables. So I allocate it like this: StrukturaDrawing* Wsk; Wsk = (StrukturaDrawing*)malloc(sizeof(StrukturaDrawing)); if (!Wsk) { printf("Error\n"); } And it doesn't returning error and also works great with other functions, it works the way I wanted it to work so finally i wanted to free that memory and here is problem because in Debug Mode compilator bitches: First-chance exception at 0x102d12b4 in GTK.exe: 0xC0000005: Access violation reading location 0xfffffffc. Unhandled exception at 0x102d12b4 in GTK.exe: 0xC0000005: Access violation reading location 0xfffffffc. I connect callback to my function, like that: g_signal_connect(G_OBJECT(Okno), "destroy", G_CALLBACK(Wyjscie), Wsk); Function which is suppose to free memory and close program: void Wyjscie(GtkWindow* window, GdkEvent* event, StrukturaDrawing* data) { gtk_main_quit(); free(data); data = NULL; } Any help really appreciated.

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  • Codeigniter xss_clean dilemma

    - by Henson
    I know this question has been asked over and over again, but I still haven't found the perfect answer for my liking, so here it goes again... I've been reading lots and lots polarizing comments about CI's xss_filter. Basically majority says that it's bad. Can someone elaborate how it's bad, or at least give 1 most probable scenario where it can be exploited? I've looked at the security class in CI 2.1 and I think it's pretty good as it doesn't allow malicious strings like document.cookie, document.write, etc. If the site has basically non-html presentation, is it safe to use global xss_filter (or if it's REALLY affecting performance that much, use it on per form post basis) before inserting to database ? I've been reading about pros and cons about whether to escape on input/output with majority says that we should escape on output only. But then again, why allow strings like <a href="javascript:stealCookie()">Click Me</a> to be saved in the database at all? The one thing I don't like is javascript: and such will be converted to [removed]. Can I extend the CI's security core $_never_allowed_str arrays so that the never allowed strings return empty rather than [removed]. The best reasonable wrongdoing example of this I've read is if a user has password of javascript:123 it will be cleaned into [removed]123 which means string like this document.write123 will also pass as the user's password. Then again, what is the odds of that to happen and even if it happens, I can't think of any real harm that can do to the site. Thanks

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  • Java reflection Method invocations yield result faster than Fields?

    - by omerkudat
    I was microbenchmarking some code (please be nice) and came across this puzzle: when reading a field using reflection, invoking the getter Method is faster than reading the Field. Simple test class: private static final class Foo { public Foo(double val) { this.val = val; } public double getVal() { return val; } public final double val; // only public for demo purposes } We have two reflections: Method m = Foo.class.getDeclaredMethod("getVal", null); Field f = Foo.class.getDeclaredField("val"); Now I call the two reflections in a loop, invoke on the Method, and get on the Field. A first run is done to warm up the VM, a second run is done with 10M iterations. The Method invocation is consistently 30% faster, but why? Note that getDeclaredMethod and getDeclaredField are not called in the loop. They are called once and executed on the same object in the loop. I also tried some minor variations: made the field non-final, transitive, non-public, etc. All of these combinations resulted in statistically similar performance. Edit: This is on WinXP, Intel Core2 Duo, Sun JavaSE build 1.6.0_16-b01, running under jUnit4 and Eclipse.

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  • How to determine which element(s) are visible in an overflowed <div>

    - by jjross
    Basically, I'm trying to implement a system that behaves similar to the reading pane that's built into the Google Reader interface. If you haven't seen it, Google Reader presents each article in a separate box and as you scroll it highlights the current box (and marks the article as read). In addition to this, you can move forward or backward in the article list by clicking the previous and next buttons in the UI. I've basically figured out how to do most of the functionality. However, I'm not sure how I can determine which of my divs is currently visible in in the scrollable pane. I have a div that is set to overflow:auto. Inside of this div, there are other divs, each one containing a piece of content. I've used the following jquery plugin to make everything scroll based on a click of the "next" or "previous" button and it works like a charm: http://demos.flesler.com/jquery/serialScroll/ But I can't tell which div has "focus" in the scrollable pane. I'd like to be able to do this for two reasons. I'd like to highlight the item that the user is currently reading (similar to Google Reader). I need to do this regardless of whether or not they used the plugin to get there or used the browser's scroll bar. I need to be able to tell the plugin which item has focus so that my call to scroll to the "next" pane actually uses the currently viewed pane (and not just the previous pane that the plugin scrolled from). I've tried doing some searching but I can't seem to figure out a way to do this. I found lots of ways to scroll to a particular item, but I can't find a way to determine which element is visible in an overflowed div. If I can determine which items are visible, I can (probably) figure out the rest. I'm using jquery if that helps. Thanks!

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  • .Net file writing and string splitting issues

    - by sagar
    I have a requirement where the file should be split using a given character. Default splitting options are CRLF and LF In both these cases I am splitting the line by \r\n and \r respectively. Also I have requirement where any size of file should be processed. (Processing is basically inserting the given string in a file at given position). For this I am reading the file in chunk of 1024 bytes. Then I am applying the string.Split() method. Split() method gives options for ignoring white spaces and none. I have to add back these line break characters to the line. for this I am using a binary writer and I am writing the byte array to the new file. Issue:- 1) When line break is CRLF, and the split option is NONE, while spaces are also added in the splitted array. Second option is given (to ignore white spaces) CRLF works properly. 2)Bit ignoring white space option creates other problems, as I am reading the file byte by byte I can't ignore a white space. 3)When line break characters are other than default(e.g. '|', a null value is prepended to the resulting line. Can anybody give solution to my issues?

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  • Read XML Files using LINQ to XML and Extension Methods

    - by psheriff
    In previous blog posts I have discussed how to use XML files to store data in your applications. I showed you how to read those XML files from your project and get XML from a WCF service. One of the problems with reading XML files is when elements or attributes are missing. If you try to read that missing data, then a null value is returned. This can cause a problem if you are trying to load that data into an object and a null is read. This blog post will show you how to create extension methods to detect null values and return valid values to load into your object. The XML Data An XML data file called Product.xml is located in the \Xml folder of the Silverlight sample project for this blog post. This XML file contains several rows of product data that will be used in each of the samples for this post. Each row has 4 attributes; namely ProductId, ProductName, IntroductionDate and Price. <Products>  <Product ProductId="1"           ProductName="Haystack Code Generator for .NET"           IntroductionDate="07/01/2010"  Price="799" />  <Product ProductId="2"           ProductName="ASP.Net Jumpstart Samples"           IntroductionDate="05/24/2005"  Price="0" />  ...  ...</Products> The Product Class Just as you create an Entity class to map each column in a table to a property in a class, you should do the same for an XML file too. In this case you will create a Product class with properties for each of the attributes in each element of product data. The following code listing shows the Product class. public class Product : CommonBase{  public const string XmlFile = @"Xml/Product.xml";   private string _ProductName;  private int _ProductId;  private DateTime _IntroductionDate;  private decimal _Price;   public string ProductName  {    get { return _ProductName; }    set {      if (_ProductName != value) {        _ProductName = value;        RaisePropertyChanged("ProductName");      }    }  }   public int ProductId  {    get { return _ProductId; }    set {      if (_ProductId != value) {        _ProductId = value;        RaisePropertyChanged("ProductId");      }    }  }   public DateTime IntroductionDate  {    get { return _IntroductionDate; }    set {      if (_IntroductionDate != value) {        _IntroductionDate = value;        RaisePropertyChanged("IntroductionDate");      }    }  }   public decimal Price  {    get { return _Price; }    set {      if (_Price != value) {        _Price = value;        RaisePropertyChanged("Price");      }    }  }} NOTE: The CommonBase class that the Product class inherits from simply implements the INotifyPropertyChanged event in order to inform your XAML UI of any property changes. You can see this class in the sample you download for this blog post. Reading Data When using LINQ to XML you call the Load method of the XElement class to load the XML file. Once the XML file has been loaded, you write a LINQ query to iterate over the “Product” Descendants in the XML file. The “select” portion of the LINQ query creates a new Product object for each row in the XML file. You retrieve each attribute by passing each attribute name to the Attribute() method and retrieving the data from the “Value” property. The Value property will return a null if there is no data, or will return the string value of the attribute. The Convert class is used to convert the value retrieved into the appropriate data type required by the Product class. private void LoadProducts(){  XElement xElem = null;   try  {    xElem = XElement.Load(Product.XmlFile);     // The following will NOT work if you have missing attributes    var products =         from elem in xElem.Descendants("Product")        orderby elem.Attribute("ProductName").Value        select new Product        {          ProductId = Convert.ToInt32(            elem.Attribute("ProductId").Value),          ProductName = Convert.ToString(            elem.Attribute("ProductName").Value),          IntroductionDate = Convert.ToDateTime(            elem.Attribute("IntroductionDate").Value),          Price = Convert.ToDecimal(elem.Attribute("Price").Value)        };     lstData.DataContext = products;  }  catch (Exception ex)  {    MessageBox.Show(ex.Message);  }} This is where the problem comes in. If you have any missing attributes in any of the rows in the XML file, or if the data in the ProductId or IntroductionDate is not of the appropriate type, then this code will fail! The reason? There is no built-in check to ensure that the correct type of data is contained in the XML file. This is where extension methods can come in real handy. Using Extension Methods Instead of using the Convert class to perform type conversions as you just saw, create a set of extension methods attached to the XAttribute class. These extension methods will perform null-checking and ensure that a valid value is passed back instead of an exception being thrown if there is invalid data in your XML file. private void LoadProducts(){  var xElem = XElement.Load(Product.XmlFile);   var products =       from elem in xElem.Descendants("Product")      orderby elem.Attribute("ProductName").Value      select new Product      {        ProductId = elem.Attribute("ProductId").GetAsInteger(),        ProductName = elem.Attribute("ProductName").GetAsString(),        IntroductionDate =            elem.Attribute("IntroductionDate").GetAsDateTime(),        Price = elem.Attribute("Price").GetAsDecimal()      };   lstData.DataContext = products;} Writing Extension Methods To create an extension method you will create a class with any name you like. In the code listing below is a class named XmlExtensionMethods. This listing just shows a couple of the available methods such as GetAsString and GetAsInteger. These methods are just like any other method you would write except when you pass in the parameter you prefix the type with the keyword “this”. This lets the compiler know that it should add this method to the class specified in the parameter. public static class XmlExtensionMethods{  public static string GetAsString(this XAttribute attr)  {    string ret = string.Empty;     if (attr != null && !string.IsNullOrEmpty(attr.Value))    {      ret = attr.Value;    }     return ret;  }   public static int GetAsInteger(this XAttribute attr)  {    int ret = 0;    int value = 0;     if (attr != null && !string.IsNullOrEmpty(attr.Value))    {      if(int.TryParse(attr.Value, out value))        ret = value;    }     return ret;  }   ...  ...} Each of the methods in the XmlExtensionMethods class should inspect the XAttribute to ensure it is not null and that the value in the attribute is not null. If the value is null, then a default value will be returned such as an empty string or a 0 for a numeric value. Summary Extension methods are a great way to simplify your code and provide protection to ensure problems do not occur when reading data. You will probably want to create more extension methods to handle XElement objects as well for when you use element-based XML. Feel free to extend these extension methods to accept a parameter which would be the default value if a null value is detected, or any other parameters you wish. NOTE: You can download the complete sample code at my website. http://www.pdsa.com/downloads. Choose “Tips & Tricks”, then "Read XML Files using LINQ to XML and Extension Methods" from the drop-down. Good Luck with your Coding,Paul D. Sheriff  

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  • From Bluehost to WP Engine, My WordPress Story

    - by thatjeffsmith
    This is probably the longest blog post I’ve written in a LONG time. And if you’re used to coming here for the Oracle stuff, this post is not about that. It’s about my blog, and the stuff under the hood that makes it run, AKA WordPress. If you want to skip to the juicy stuff, then use these shortcuts: My Site Slowed Down How I Moved to WP Engine How WP Engine ‘Hooked’ Me Why WP Engine? I started thatJeffSmith.com on May 28th, 2010. I had been already been blogging for several years, but a couple of really smart people I respected (Andy, Brent – thanks again!) suggested that I take ownership of my content and begin building my personal brand. I thought that was a good idea, and so I signed up for service with bluehost. Bluehost makes setting up a WordPress site very, very easy. And, they continued to be easy to work with for the past 2 years. I would even recommend them to anyone looking to host their own WordPress install/site. For $83.40, I purchased a year’s worth of service and my domain name registration – a very good value. And then last year I paid $107.40 for another year’s services. And when that year expired I paid another $190.80 for an additional two year’s service in advance. I had been up to that point, getting my money’s worth. And then, just a few weeks ago… My Site Slowed to a Crawl That spike was from an April Fool's Day Post, I think Why? Well, when I first started blogging, I had the same problem that most beginner bloggers have – not many readers. In my first year of blogging, I think the highest number of readers on a single day was about 125. I remember that day as I was very excited to break 100! Bluehost was very reliable, serving up my content with maybe a total of 3-4 outages in the past 2 years. Support was usually very prompt with answers and solutions, and I love their ‘Chat now’ technology – much nicer than message boards only or pay-to-talk phone support. In the past 6 months however, I noticed a couple of things: daily traffic was increasing – woohoo! my service was experiencing severe CPU throttling – doh! To be honest, I wasn’t aware the throttling was occuring, but I did know that the response time of my blog was starting to lag. Average load times were approaching 20-30 seconds. Not good when good sites are loading in 5 seconds or less. And just this past week, in getting ready to launch a new website for work that sucked in an RSS feed from my blog, the new page was left waiting for more than a minute. Not good! In fact my boss asked, why aren’t you blogging on Blogger? Ugh. I tried a few things to fix the problem: I paid for a premium WordPress theme – Themify’s Grido (thanks to @SQLRockstar for the heads-up) I installed a couple of WP caching plugins I read every WP optimization blog post I could get my greedy little eyes on However, at the same time I was also getting addicted to WordPress bloggers talking about all the cool things you could do with your blog. As a result I had at one point about 30 different plugins installed. WordPress runs on MySQL, and certain queries running via these plugins were starving for CPU. Plugins that would be called every page load meant that as more people clicked on my site, the more CPU I needed. I’m not stupid, so I eventually figured out that maybe less plugins was better, and was able to go down to just 20. But still, the site was running like a dog. CPU Throttling, makes MySQL wait to run a query Bluehost runs shared servers. Your site runs on the same box that several hundred (or thousand?) other services are running on. If you take more CPU than they think you should have, they will limit your service by making you stand in line for CPU, AKA ‘throttling.’ This is not bad. This business model allows them to serve many, many users for a very fair price. It works great until, well, until it doesn’t. I noticed in the last week that for every minute of service, I was being throttled between 60 and 300 seconds. If there were 5 MySQL processes running, then every single one of them were being held in check. The blog visitor notice this as their page requests would take a minute or more to be answered. Bluehost unfortunately doesn’t offer dedicated server hosting, so there was no real upgrade path for me follow and remain one of their customers. So what was I to do? Uninstall every plugin and hope the site sped up? Ask for people to take turns on my blog? I decided to spend my way out of the problem. I signed up for service with WP Engine and moved ThatJeffSmith.com The first 2 months are free, and after that it’s about $29/month to run my site on their system. My math tells me that’s a good bit more expensive than what Bluehost was charging me – to the tune of about 300% more a month. Oh, and I should just say that my blog is a personal blog even though I talk about work stuff here. I don’t get paid for blogging, I don’t sell ads, and I don’t expense the service fees – this is my personal passion. So is it worth it? In the first 4 days, it seems to be totally worth it. Load times have gone from 20-30 seconds to less than 5 seconds. A few folks have told me via Twitter that they notice faster page loads. I anticipate this will indirectly lead to more traffic as Google penalizes you in search results if your site is too slow, and of course some folks won’t even bother waiting more than 5-10 seconds. I noticed right away that writing posts, uploading pictures, and just using the WordPress dashboard in general was much more responsive. So writing is less of a chore now, which means I won’t have a good reason not to write How I Moved to WP Engine I signed up for the service and registered my domain. I then took a full export of my ‘old’ site by doing a FTP GET of all my files, then did a MySQL database backup, exported my WordPress Theme settings to a .zip file, and then finally used the WordPress ‘Export’ feature. I then used the WordPress ‘Import’ on the new site to load up my posts. Then I uploaded the theme .zip package from Themify. Then I FTP’d the ‘wp-content’ directory up to my new server using SFTP (WP Engine only supports secure FTP – good on them!) Using a temporary URL to see my new site, I was able to confirm that everything looked mostly OK – I’ll detail the challenges and issues of fixing the content next – but then it was time to ‘flip the switch.’ I updated the IP address that the DNS lookup tables use to route traffic to my new server. In a matter of minutes the DNS servers around the world were updated and it was time to see the new site! But It Was ‘Broken’ I had never moved a website before, and in my rush to update the DNS, I had changed the records without really finding out what I was supposed to do first. After re-reading the directions provided by WP Engine and following the guidance of their support engineer, I realized I had needed to set the CNAME (Alias) ‘www’ record to point to a different URL than the ‘www.thatjeffsmith.com’ entry I had set. Once corrected the site was up and running in less than a minute. Then It Was Only Mostly Broken Many of my plugins weren’t working. Apparently just ftp’ing the wp-content directory up wasn’t the proper way to re-install the plugin. I suspect file permissions or file ownership wasn’t proper. Some plug-ins were working, many had their settings wiped to the defaults, and a few just didn’t work again. I had to delete the directory of the plug-in manually via SFTP, and then use the WP Dashboard to install it from scratch. And here was my first ‘lesson’ – don’t switch the DNS records until you’ve completely tested your new site. I wasn’t able to navigate the old WP console to review my plug-in settings. Thankfully I was able to use the Wayback Machine to reverse engineer some things, and of course most plug-ins aren’t that complicated to setup to begin with. An example of one that I had to redo from scratch is the ‘Twitter @Anywhere Plus’ plugin that I use to create the form that allows folks to tweet a post they enjoyed at the end of each story. How WP Engine ‘Hooked’ Me I actually signed up with another provider first. They ranked highly in Google searches and a few Tweeps recommended them to me. But hours after signing up and I still didn’t have sever reyady, I was ready to give up on them. They offered no chat or phone support – only mail and message boards. And the message boards were rife with posts about how the service had gone downhill in the past 6 months. To their credit, they did make it easy to cancel, although I did have to do so via email as their website ‘cancel’ button was non-existent. Within minutes of activating my WP Engine account I had received my welcome message and directions on how to get started. I was able to see my staged website right away. They also did something very cool before I even got started – they looked at my existing site and told me by how much they could improve its performance. The proof is in the web pudding. I like this for a few reasons, but primarily I liked their business model. It told me they knew what they were doing, and that they were willing to put their money where their mouth was. This was further evident by their 60-day money back guarantee. And if I understand it correctly, they don’t even take your money until after that 60 day period is over. After a day, I was welcomed by the WP Engine social media team, and was given the opportunity to subscribe to their newsletter and follow their account on Twitter. I noticed their Twitter team is sure to post regular WordPress tips several times a day. It’s not just an account that’s setup for the sake of having a Twitter presence. These little things add up and give me confidence in my decision to choose them as my hosting partner. ‘Partner’ – that’s a lot nicer word than just ‘service provider,’ isn’t it? Oh, and they offered me a t-shirt. Don’t ever doubt the power of a ‘free’ t-shirt! How awesome is this e-mail, from a customer perspective? I wasn’t really expecting any of this. Exceeding expectations before I have even handed over a single dollar seems like a pretty good business plan. This is how you treat customers. Love them to death, and they reward you with loyalty. But Jeff, You Skipped a Piece Here, Why WP Engine? I found them on one of those ‘Top 10′ list posts, and pulled up their webpage. I noticed they offered a specialized service – they host WordPress installs, and that’s it. Their servers are tuned specifically for running WordPress. They had in bolded text, things like ‘INSANELY FAST. INFINITELY SCALABLE.’ and ‘LIGHTNING SPEED.’ And then they offered insurance against hackers and they took care of automatic backups and restores. The only drawbacks I have noticed so far relate to plugins I used that have been ‘blacklisted.’ In order to guarantee that ‘lightning’ speed, they have banned the use of the CPU-suckiest plugins. One of those is the ‘Related Posts’ plugin. So if you are a subscriber and are reading this in your email, you’ll notice there’s no links back to my blog to continue reading other related stories. Since that referral traffic is very small single-digit for my site, I decided that I’m OK with that. I’d rather have the warp-speed page loads. Again, I think that will lead to higher traffic down the road. In 50+ days I will need to decide if WP Engine is a permanent solution. I’ll be sure to update this post when that time comes and let y’all know how it turns out.

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