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• Using Multiple File Handles for Single File

  - by Ryan Rosario

  I have an O(n^2) operation that requires me to read line i from a file, and then compare line i to every line in the file. This repeats for all i. I wrote the following code to do this with 2 file handles, but it does not yield the result I am looking for. I imagine this is a simple error on my part. IN1 = open("myfile.dat","r") IN2 = open("myfile.dat","r") for line1 in IN1: for line2 in IN2: print line1.strip(), line2.strip() IN1.close() IN2.close() The result: Hello Hello Hello World Hello This Hello is Hello an Hello Example Hello of Hello Using Hello Two Hello File Hello Pointers Hello to Hello Read Hello One Hello File The output should contain 15^2 lines.

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• Is fwrite non-blocking?

  - by John Michaels

  Before calling fflush can I consider fwrite to be = a non-blocking write? If not, why not and what are my alternatives?

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• Modify Executing Jar file

  - by pinkynobrain

  Hello Stack Overflow friends. I have a simple problem which i fear doesnt have a simple solution and i need advice as to how to proceed. I am developing a java application packaged as and executable JAR but it requires to modify some of its JAR file contents during execution. At this stage i hit a problem because some OS lock the file preventing writes to it. It is essential that the user sees an updated version of the jar file by the time the application exits allthough i can be pretty flexible as to how to achieve this. A clean and efficient solution is obviously prefereable but portability is the only hard requirement. The following are three approaches i can see to solving the problem, feel free to comment on them or suggest others. Tell Java to unlock the JAR file for writing(this doesnt seem possible but it would be the easyest solution) Copy the executable class files to a tempory file on application startup, use a class loader to load these files and unload the ones from the initial JAR file.(Not had much experience with the classloaders but hopefully the JVM would then be smart enough to realize that the original JAR is nolonger in use and so unlock it) Put a Second executable JAR File inside the First, on startup extract the inner jar to e temporaryfile, invoke a new java process and pass it the location of the Outer JAR, first process exits, second process modifys the Outer jar unincumbered.(This will work but im not sure there is a platform independant way of one java app invoking another) I know this is a weird question but any help would be appreciated.

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• What is the root directory OR how do I set the directory in DotNetZip

  - by Chris

  where does DotNetZip get it's root directory for saving. All the save examples don't show the directory. My goal is to recurse a folder and subfolders. In each folder I want to zip all the files into one zip and delete the source files. private void CopyFolder(string srcPath, string dstPath) { if (!Directory.Exists(dstPath)) Directory.CreateDirectory(dstPath); string[] files = Directory.GetFiles(srcPath); string msg; string zipFileName; using (ZipFile z = new ZipFile(Path.Combine(srcPath,String.Format("Archive{0:yyyyMMdd}.zip", DateTime.Now)))) { z.ReadProgress += new EventHandler<ReadProgressEventArgs>(z_ReadProgress); foreach (string file in files) { FileInfo fi = new FileInfo(file); AddLog(String.Format("Adding {0}", file)); z.AddFile(file); } //z.Save(Path.Combine(srcPath, String.Format("Archive{0:yyyyMMdd}.zip", DateTime.Now))); z.Save(); if (deleteSource) { foreach (string file in files) { File.Delete(file); } } zipFileName = z.Name; } if (!compressOnly) File.Copy(Path.Combine(srcPath,zipFileName), Path.Combine(dstPath, Path.GetFileName(zipFileName))); string[] folders = Directory.GetDirectories(sourcePath); foreach (string folder in folders) { string name = Path.GetFileName(folder); string dest = Path.Combine(dstPath, name); Console.WriteLine(ln); log.Add(ln); msg = String.Format("{3}{4}Start Copy: {0}{4}Directory: {1}{4}To: {2}", DateTime.Now.ToString("G"), name, dest, ln, Environment.NewLine); AddLog(msg); if (recurseFolders) CopyFolder(folder, dest); msg = String.Format("Copied Directory: {0}{4}To: {1}\nAt: {2}{3}", folder, dest, DateTime.Now.ToString("G"), Environment.NewLine); AddLog(msg); } }

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• implementing a download manager that supports resuming

  - by Idan K

  hi, I intend on writing a small download manager in C++ that supports resuming (and multiple connections per download). From the info I gathered so far, when sending the http request I need to add a header field with a key of "Range" and the value "bytes=startoff-endoff". Then the server returns a http response with the data between those offsets. So roughly what I have in mind is to split the file to the number of allowed connections per file and send a http request per splitted part with the appropriate "Range". So if I have a 4mb file and 4 allowed connections, I'd split the file to 4 and have 4 http requests going, each with the appropriate "Range" field. Implementing the resume feature would involve remembering which offsets are already downloaded and simply not request those. Is this the right way to do this? What if the web server doesn't support resuming? (my guess is it will ignore the "Range" and just send the entire file) When sending the http requests, should I specify in the range the entire splitted size? Or maybe ask smaller pieces, say 1024k per request? When reading the data, should I write it immediately to the file or do some kind of buffering? I guess it could be wasteful to write small chunks. Should I use a memory mapped file? If I remember correctly, it's recommended for frequent reads rather than writes (I could be wrong). Is it memory wise? What if I have several downloads simultaneously? If I'm not using a memory mapped file, should I open the file per allowed connection? Or when needing to write to the file simply seek? (if I did use a memory mapped file this would be really easy, since I could simply have several pointers). Note: I'll probably be using Qt, but this is a general question so I left code out of it.

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• Prepend lines to file in Java

  - by folone

  Is there a way to prepend a line to the File in Java, without creating a temporary file, and writing the needed content to it?

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• How can I read/write data from a file?

  - by samy

  I'm writing a simple chrome extension. I need to create the ability to add sites URLs to a list, or read from the list. I use the list to open the sites in the new tabs. I'm looking for a way to have a data file I can write to, and read from. I was thinking on XML. I read there is a problem changing the content of files with Javascript. Is XML the right choice for this kinda thing? I should add that there is no web server, and the app will run locally, so maybe the problem websites are having are not same as this. Before I wrote this question, I tried one thing, and started to feel insecure because it didn't work. I made a XML file called Site.xml: <?xml version="1.0" encoding="utf-8" ?> <Sites> <site> <url> http://www.sulamacademy.com/AddMsgForum.asp?FType=273171&SBLang=0&WSUAccess=0&LocSBID=20375 </url> </site> <site> <url> http://www.wow.co.il </url> </site> <site> <url> http://www.Google.co.il </url> </site> I made this script to read the data from him, and put in on the html file. function LoadXML() { var ajaxObj = new XMLHttpRequest(); ajaxObj.open('GET', 'Sites.xml', false); ajaxObj.send(); var myXML = ajaxObj.responseXML; document.write('<table border="2">'); var prs = myXML.getElementsByTagName("site"); for (i = 0; i < prs.length; i++) { document.write("<tr><td>"); document.write(prs[i].getElementsByName("url")[0].childNode[0].nodeValue); document.write("</td></tr>"); } document.write("</table"); }

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• A couple questions using fwrite/fread with data structures

  - by Nazgulled

  Hi, I'm using fwrite() and fread() for the first time to write some data structures to disk and I have a couple of questions about best practices and proper ways of doing things. What I'm writing to disk (so I can later read it back) is all user profiles inserted in a Graph structure. Each graph vertex is of the following type: typedef struct sUserProfile { char name[NAME_SZ]; char address[ADDRESS_SZ]; int socialNumber; char password[PASSWORD_SZ]; HashTable *mailbox; short msgCount; } UserProfile; And this is how I'm currently writing all the profiles to disk: void ioWriteNetworkState(SocialNetwork *social) { Vertex *currPtr = social->usersNetwork->vertices; UserProfile *user; FILE *fp = fopen("save/profiles.dat", "w"); if(!fp) { perror("fopen"); exit(EXIT_FAILURE); } fwrite(&(social->usersCount), sizeof(int), 1, fp); while(currPtr) { user = (UserProfile*)currPtr->value; fwrite(&(user->socialNumber), sizeof(int), 1, fp); fwrite(user->name, sizeof(char)*strlen(user->name), 1, fp); fwrite(user->address, sizeof(char)*strlen(user->address), 1, fp); fwrite(user->password, sizeof(char)*strlen(user->password), 1, fp); fwrite(&(user->msgCount), sizeof(short), 1, fp); break; currPtr = currPtr->next; } fclose(fp); } Notes: The first fwrite() you see will write the total user count in the graph so I know how much data I need to read back. The break is there for testing purposes. There's thousands of users and I'm still experimenting with the code. My questions: After reading this I decided to use fwrite() on each element instead of writing the whole structure. I also avoid writing the pointer to to the mailbox as I don't need to save that pointer. So, is this the way to go? Multiple fwrite()'s instead of a global one for the whole structure? Isn't that slower? How do I read back this content? I know I have to use fread() but I don't know the size of the strings, cause I used strlen() to write them. I could write the output of strlen() before writing the string, but is there any better way without extra writes?

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• read a file with both text and binary information in .Net

  - by Yin Zhu

  I need to read binary PGM image files. Its format: P5 # comments nrows ncolumns max-value binary values start at this line. (totally nrows*ncolumns bytes/unsigned char) I know how to do it in C or C++ using FILE handler by reading several lines first and read the binary block. But don't know how to do it in .Net.

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• Reading a file from a jar, or anywhere on the classpath?

  - by Stefan Kendall

  I'm trying to build an application that builds a resource file into a jar, but I'd like to have the project runnable within eclipse. I have a basic maven 2 structure for my project, and I'm unsure how to read in the file such that it's found and used when run from the JAR or from within eclipse. Thought? Structure: src/main/java src/main/resources/file.txt Current reading method: getClass().getResourceAsStream("/file.txt") Is there reading method that will pick up src/main/resources/*, as well as the root level of the JAR (where resources are deployed)?

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• loading data from file into 2d array

  - by Chris

  I am just starting with perl and would like some help with arrays please. I am reading lines from a data file and splitting the line into fields: open (INFILE, $infile); do { my $linedata = <INFILE>; my @data= split ',',$linedata; .... } until eof; I then want to store the individual field values (in @data) in and array so that the array looks like the input data file ie, the first "row" of the array contains the first line of data from INFILE etc. Each line of data from the infile contains 4 values, x,y,z and w and once the data are all in the array, I have to pass the array into another program which reads the x,y,z,w and displays the w value on a screen at the point determined by the x,y,z value. I can not pas the data to the other program on a row-by-row basis as the program expects the data to in a 2d matrtix format. Any help greatly appreciated. Chris

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• Is it possible for competing file access to cause deadlock in Java?

  - by BlairHippo

  I'm chasing a production bug that's intermittent enough to be a real bastich to diagnose properly but frequent enough to be a legitimate nuisance for our customers. While I'm waiting for it to happen again on a machine set to spam the logfile with trace output, I'm trying to come up with a theory on what it could be. Is there any way for competing file read/writes to create what amounts to a deadlock condition? For instance, let's say I have Thread A that occasionally writes to config.xml, and Thread B that occasionally reads from it. Is there a set of circumstances that would cause Thread B to prevent Thread A from proceeding? My thanks in advance to anybody who helps with this theoretical fishing expedition. Edit: To answer Pyrolistical's questions: the code isn't using Filelock, and is running on a WinXP machine.

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• 'Programming by Coincidence' Excercise: Java File Writer

  - by Tapas

  I just read the article Programming by Coincidence. At the end of the page there are excercises. A few code fragments that are cases of "programming by coincidence". But I cant figure out the error in this piece: This code comes from a general-purpose Java tracing suite. The function writes a string to a log file. It passes its unit test, but fails when one of the Web developers uses it. What coincidence does it rely on? public static void debug(String s) throws IOException { FileWriter fw = new FileWriter("debug.log", true); fw.write(s); fw.flush(); fw.close(); } What is wrong about this?

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• Get last n lines of a file with Python, similar to tail

  - by Armin Ronacher

  I'm writing a log file viewer for a web application and for that I want to paginate through the lines of the log file. The items in the file are line based with the newest item on the bottom. So I need a tail() method that can read n lines from the bottom and supports an offset. What I came up with looks like this: def tail(f, n, offset=0): """Reads a n lines from f with an offset of offset lines.""" avg_line_length = 74 to_read = n + offset while 1: try: f.seek(-(avg_line_length * to_read), 2) except IOError: # woops. apparently file is smaller than what we want # to step back, go to the beginning instead f.seek(0) pos = f.tell() lines = f.read().splitlines() if len(lines) >= to_read or pos == 0: return lines[-to_read:offset and -offset or None] avg_line_length *= 1.3 Is this a reasonable approach? What is the recommended way to tail log files with offsets?

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• PHP is unable to open a file for writing - but it does exist

  - by asdasdas

  I am trying to write to a file. I do a file_exists check on it before i do fopen and it comes up true: the file does exist. However, the file fails this code and gives me the error every time: $handle = fopen($filename, 'w'); if($handle) { flock($handle, LOCK_EX); fwrite($handle, $contents); } else { echo 'ERROR: Unable to open the file for writing.',PHP_EOL; exit(); } flock($handle, LOCK_UN); fclose($handle); Is there a way I can get more specific error details as to why this file does not let me open it for writing? I know that the filename is legit, but for some reason it just wont let me write to it. I do have write permissions, I was able to write and write over another file.

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• What should be the ideal number of parallel java threads for copying a large set of files from a qua

  - by ukgenie

  What should be the ideal number of parallel java threads for copying a large set of files from a quad core linux box to an external shared folder? I can see that with a single thread it is taking a hell lot of time to move the files one by one. Multiple threads is improving the copy performance, but I don't know what should be the exact number of threads. I am using Java executor service to create the thread pool.

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• Persist changes in C

  - by Mohit Deshpande

  I am developing a database-like application that stores a a structure containing: struct Dictionary { char *key; char *value; struct Dictionary *next; }; As you can see, I am using a linked list to store information. But the problem begins when the user exits out of the program. I want the information to be stored somewhere. So I was thinking of storing the linked list in a permanent or temporary file using fopen, then, when the user starts the program, retrieve the linked list. Here is the method that prints the linked list to the console: void PrintList() { int count = 0; struct Dictionary *current; current = head; if (current == NULL) { printf("\nThe list is empty!"); return; } printf(" Key \t Value\n"); printf(" ======== \t ========\n"); while (current != NULL) { count++; printf("%d. %s \t %s\n", count, current->key, current->value); current = current->next; } } So I am thinking of modifying this method to print the information through fprintf instead of printf and then the program would just get the infomation from the file. Could someone help me on how I can read and write to this file? What kind of file should it be, temporary or regular? How should I format the file (like I was thinking of just having the key first, then the value, then a newline character)?

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• Load binary file using fstream

  - by Kirill V. Lyadvinsky

  I'm trying to load binary file using fstream in the following way: #include <iostream #include <fstream #include <iterator #include <vector using namespace std; int main() { basic_fstream<uint32_t file( "somefile.dat", ios::in|ios::binary ); vector<uint32_t buffer; buffer.assign( istream_iterator<uint32_t, uint32_t( file ), istream_iterator<uint32_t, uint32_t() ); cout << buffer.size() << endl; return 0; } But it doesn't work. In Ubuntu it crashed with std::bad_cast exception. In MSVC++ 2008 it just prints 0. I know that I could use file.read to load file, but I want to use iterator and operator>> to load parts of the file. Is that possible? Why the code above doesn't work?

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• EDIT Control Showing Squares Instead Of Returns

  - by Nathan Campos

  I'm playing a little bit with PocketC by doing a simple text editor. But with this code to read and to display the contents of the file on the EDIT control: int filehandle; int file_len; string file_mode; initComponents() { createctrl("EDIT", "test", 2, 1, 0, 24, 70, 25, TEXTBOX); wndshow(TEXTBOX, SW_SHOW); guigetfocus(); } main() { filehandle = fileopen(OpenFileDlg("Plain Text Files (*.txt)|*.txt; All Files (*.*)|*.*"), 0, FILE_READWRITE); file_len = filegetlen(filehandle); if(filehandle == -1) { MessageBox("File Could Not Be Found!", "Error", 3, 1); } initComponents(); editset(TEXTBOX, fileread(filehandle, file_len)); } It's all ok, but my test file, now have returns: Hello, World! PocketC Test Of My Editor Then when I open this file on the editor, instead of returns, I just see two squares(that means that it's a unknown character for that control), but if I change the control to a STATIC, it does he returns ok, but I can't edit the text if I use a STATIC. Then I want to know what I need to do to do the returns instead of showing those squares.

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• Python unicode problem

  - by Somebody still uses you MS-DOS

  I'm receiving some data from a ZODB (Zope Object Database). I receive a mybrains object. Then I do: o = mybrains.getObject() and I receive a "Person" object in my project. Then, I can do b = o.name and doing print b on my class I get: José Carlos and print b.name.__class__ <type 'unicode'> I have a lot of "Person" objects. They are added to a list. names = [o.nome, o1.nome, o2.nome] Then, I trying to create a text file with this data. delimiter = ';' all = delimiter.join(names) + '\n' No problem. Now, when I do a print all I have: José Carlos;Jonas;Natália Juan;John But when I try to create a file of it: f = open("/tmp/test.txt", "w") f.write(all) I get an error like this (the positions aren't exaclty the same, since I change the names) UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in position 84: ordinal not in range(128) If I can print already with the "correct" form to display it, why I can't write a file with it? Which encode/decode method should I use to write a file with this data? I'm using Python 2.4.5 (can't upgrade it)

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• Why does File::Slurp return a scalar when it should return a list?

  - by BrianH

  I am new to the File::Slurp module, and on my first test with it, it was not giving the results I was expecting. It took me a while to figure it out, so now I am interested in why I was seeing this certain behavior. My call to File::Slurp looked like this: my @array = read_file( $file ) || die "Cannot read $file\n"; I included the "die" part because I am used to doing that when opening files. My @array would always end up with the entire contents of the file in the first element of the array. Finally I took out the "|| die" section, and it started working as I expected. Here is an example to illustrate: perl -de0 Loading DB routines from perl5db.pl version 1.22 Editor support available. Enter h or `h h' for help, or `man perldebug' for more help. main::(-e:1): 0 DB<1> use File::Slurp DB<2> $file = '/usr/java6_64/copyright' DB<3> x @array1 = read_file( $file ) 0 'Licensed material - Property of IBM.' 1 'IBM(R) SDK, Java(TM) Technology Edition, Version 6' 2 'IBM(R) Runtime Environment, Java(TM) Technology Edition, Version 6' 3 '' 4 'Copyright Sun Microsystems Inc, 1992, 2008. All rights reserved.' 5 'Copyright IBM Corporation, 1998, 2009. All rights reserved.' 6 '' 7 'The Apache Software License, Version 1.1 and Version 2.0' 8 'Copyright 1999-2007 The Apache Software Foundation. All rights reserved.' 9 '' 10 'Other copyright acknowledgements can be found in the Notices file.' 11 '' 12 'The Java technology is owned and exclusively licensed by Sun Microsystems Inc.' 13 'Java and all Java-based trademarks and logos are trademarks or registered' 14 'trademarks of Sun Microsystems Inc. in the United States and other countries.' 15 '' 16 'US Govt Users Restricted Rights - Use duplication or disclosure' 17 'restricted by GSA ADP Schedule Contract with IBM Corp.' DB<4> x @array2 = read_file( $file ) || die "Cannot read $file\n"; 0 'Licensed material - Property of IBM. IBM(R) SDK, Java(TM) Technology Edition, Version 6 IBM(R) Runtime Environment, Java(TM) Technology Edition, Version 6 Copyright Sun Microsystems Inc, 1992, 2008. All rights reserved. Copyright IBM Corporation, 1998, 2009. All rights reserved. The Apache Software License, Version 1.1 and Version 2.0 Copyright 1999-2007 The Apache Software Foundation. All rights reserved. Other copyright acknowledgements can be found in the Notices file. The Java technology is owned and exclusively licensed by Sun Microsystems Inc. Java and all Java-based trademarks and logos are trademarks or registered trademarks of Sun Microsystems Inc. in the United States and other countries. US Govt Users Restricted Rights - Use duplication or disclosure restricted by GSA ADP Schedule Contract with IBM Corp. ' Why does the || die make a difference? I have a feeling this might be more of a Perl precedence question instead of a File::Slurp question. I looked in the File::Slurp module and it looks like it is set to croak if there is a problem, so I guess the proper way to do it is to allow File::Slurp to croak for you. Now I'm just curious why I was seeing these differences.

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• How to create a Java String from the contents of a file

  - by Oscar Reyes

  I've been using this idiom for some time now. And it seems to be the most wide spread at least in the sites I've visited. Does anyone have a better/different way to read a file into a string in Java. Thanks private String readFile( String file ) throws IOException { BufferedReader reader = new BufferedReader( new FileReader (file)); String line = null; StringBuilder stringBuilder = new StringBuilder(); String ls = System.getProperty("line.separator"); while( ( line = reader.readLine() ) != null ) { stringBuilder.append( line ); stringBuilder.append( ls ); } return stringBuilder.toString(); }

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• Python: Retrieve Image from MSSQL

  - by KoRkOnY

  Dear All, I'm working on a Python project that retrieves an image from MSSQL. My code is able to retrieve the images successfully but with a fixed size of 63KB. if the image is greater than that size, it just brings the first 63KB from the image! The following is my code: #!/usr/bin/python import _mssql mssql=_mssql.connect('<ServerIP>','<UserID>','<Password>') mssql.select_db('<Database>') x=1 while x==1: query="select TOP 1 * from table;" if mssql.query(query): rows=mssql.fetch_array() rowNumbers = rows[0][1] #print "Number of rows fetched: " + str(rowNumbers) for row in rows: for i in range(rowNumbers): FILE=open('/home/images/' + str(row[2][i][1]) + '-' + str(row[2][i][2]).strip() + ' (' + str(row[2][i][0]) + ').jpg','wb') FILE.write(row[2][i][4]) FILE.close() print 'Successfully downloaded image: ' + str(row[2][i][0]) + '\t' + str(row[2][i][2]).strip() + '\t' + str(row[2][i][1]) else: print mssql.errmsg() print mssql.stdmsg() mssql.close()

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• Fork in Perl not working inside a while loop reading from file

  - by Sag

  Hi, I'm running a while loop reading each line in a file, and then fork processes with the data of the line to a child. After N lines I want to wait for the child processes to end and continue with the next N lines, etc. It looks something like this: while ($w=<INP>) { # ignore file header if ($w=~m/^\D/) { next;} # get data from line chomp $w; @ws = split(/\s/,$w); $m = int($ws[0]); $d = int($ws[1]); $h = int($ws[2]); # only for some days in the year if (($m==3)and($d==15) or ($m==4)and($d==21) or ($m==7)and($d==18)) { die "could not fork" unless defined (my $pid = fork); unless ($pid) { some instructions here using $m, $d, $h ... } push @qpid,$pid; # when all processors are busy, wait for child processes if ($#qpid==($procs-1)) { for my $pid (@qpid) { waitpid $pid, 0; } reset 'q'; } } } close INP; This is not working. After the first round of processes I get some PID equal to 0, the @qpid array gets mixed up, and the file starts to get read at (apparently) random places, jumping back and forth. The end result is that most lines in the file get read two or three times. Any ideas? Thanks a lot in advance, S.

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• Windows Disk I/O Analysis

  - by Jonathon

  It appears that we are having a problem with the disk i/o speed on our Windows 2003 Enterprise Edition server (64-bit). As we were initializing a database that created two 1G tablespaces on 3 different machines, it became obvious that the two smaller machines (each 32-bit Windows 2003 Standard Edition with less RAM) killed the larger machine when creating the files. The larger machine took 10x as long to create the tablespaces than did the other machines. Now, I am left wondering how that could be. What programs or scripts would you guys recommend for tracking down the I/O problem? I think the issue may be with the controller card (all boxes are hardware RAID 10, but have different controller cards), but I would like to check the actual disk I/O speed as well, so I have some hard numbers to work with. Any help would be appreciated.

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