Question

How do I flush a FileStream to disk in Lazarus on Linux

Asked by: zakiwi

Hi there,

I am processing a lot of data (100GB) and I need to write results into client files.  The resulting program itterates through the source data and for each itteration, opens the correct results file (using TFileStream) and writes the results to the file and then free's the stream.

The program works for a while, but then starts giving errors like:

Loading /old-data/2008-09-26-151035588-AC06CAC4-4C91-4FC6-B11B-B49BDDC04BF6.DAT
Processing /old-data/2008-09-26-151035588-AC06CAC4-4C91-4FC6-B11B-B49BDDC04BF6.DAT
Master: *-
Hash  : *-
Client: *Unable to open file "/new-data/client1.idx"
Unable to open file "/new-data/client1.idx"
Unable to open file "/new-data/client1.idx"
Unable to open file "/new-data/client1.idx"
Unable to open file "/new-data/client1.idx"
Unable to open file "/new-data/client1.idx"
Unable to open file "/new-data/client1.idx"

PLEASE NOTE:
- The output file does exist, and I can open it with other applcations.
- The error only happens after the program has been running for a while
- Disk activity is high during the process, which leads me to beleive that this is a flushing issue.
- If I kill the application and start again, it works for a while.
- I am running the application as root so there shouldn't be a permissions problem

I am running debian lenny.

Any help will be appreciated

Zakiwi

This is the code that is raising the error:
 
lbIndexOpen := False;
while not lbIndexOpen do
  begin
    try
      if FileExists(FileName) then
        fStream := TFileStream.Create(FileName, fmOpenReadWrite)
      else
        fStream := TFileStream.Create(FileName, fmCreate);
      lbIndexOpen := True;
    except
      on e: Exception do
        begin
          WriteLn(E.Message);
          Sleep(500);
        end;
      end;
  end;             
                                  
1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:

Select allOpen in new window

This Question has been solved and asker verified All Experts Exchange premium technology solutions are available to subscription members.

Subscribe now for full access to Experts Exchange and get

Instant Access to this Solution

  • Plus...
  • 30 Day FREE access, no risk, no obligation
  • Collaborate with the world's top tech experts
  • Unlimited access to our exclusive solution database
  • Never be left without tech help again

Subscribe Now

Asked On
2009-01-04 at 12:14:34ID24023924
Tags

Lazarus Flush TFileStream

Topic

Free Pascal

Participating Experts
1
Points
500
Comments
8

Trusted by hundreds of thousands everyday for fast, accurate and reliable tech support.

  • "The time we save is the biggest benefit of Experts Exchange to Warner Bros. What could take multiple guys 2 hours or more each to find is accessed in around 15 minutes on Experts Exchange." Mike Kapnisakis, Warner Bros.
  • "Our team likes having a resource that is more secure than just using Google and most experts using this service really know their stuff. It's nice to look here first versus using Google." Dayna Sellner, Lockheed Martin
  • "Anytime that I've been stumped with a problem, 9 out of 10 times Experts Exchange has either the accepted solution or an open discussion of the potential solution to the problem." Kenny Red, eBay Inc.

See what Experts Exchange can do for you.

Got a question?

We've got the answer.

Experts Exchange has been collecting answers to technology questions since 1996…3 million and counting! If you have a question, chances are we already have your answer.

Screenshot of Experts Exchange Knowledgebase

Need individual assistance?

Our experts are ready to help.

If you can't find the exact answer you're looking for, ask our exclusive community of 50,000 experts. You’ll get a personalized answer from a trusted professional.

Screenshot of Experts Exchange Knowledgebase

Want to learn from the best?

Read articles from industry experts.

Thousands of free tech tips, tricks, how-to’s and tutorials are available in our peer reviewed articles section. See for yourself how smart our experts are, no login required.

Screenshot of an Article

Working on a long term project?

Store your work and research.

Save solutions to your questions, answers you’ve discovered through searching plus helpful articles in your personal knowledgebase for easy future access.

Screenshot of Experts Exchange Knowledgebase

Access the answers to your technology questions today.

Subscribe Now

30-day free trial. Register in 60 seconds.

What Makes Experts Exchange Unique?

Members of the expert community talk about why the experience at Experts Exchange is different than what you will find anywhere else.

Trusted by the world's most respected brands.

image of each brand's logo

Faithfully serving IT professionals since 1996.

Experts Exchange Logo

Try it out and discover for yourself.

Subscribe Now

30-day free trial. Register in 60 seconds.

Related Solutions

  1. flush the buffer to a file
    hi, in one of my programs i need to write blocks of data into a file, first 0's, then 1's and then some other data. basically a file wiper. i read from the original file a block of data and in the same position i write 0,1 and garbage. so as to be sure that i'm overwriting ...
  2. TFileStream
    HiCan i read with TFileStream line by line (every Line can be in different length) Example will be wellcome thank u Asi
  3. JSP  flush
    is there any necessity of flush in JSP page ? how do i flush in JSP page . whats the syntax ? because when u use JSTL and bean then you can write "out.flush()" , so in that case how can i flush ? my question is : how can i flush in my JSP page while ...
  4. Flush 101
    Hi, Please assist a brief description of what the following are generally used for: Flush previliges - Flush host - Flush logs - Flush status - Flush tables - Thanks.
  5. Logs not flushing?
    Exchange 2k3 Service Pack 2 Native Mode I have a quick question. What would cause the logs not to flush? I believe the public folders need to be backed up so they can be flushed even though RSG's don't support PF stores. What else could cause the logs not to flush even tho...

Free Tech Articles

  1. WARNING: 5 Reasons why you should NEVER fix a computer for free.
    It is in our nature to love the puzzle. We are obsessed. The lot of us. We love puzzles. We love the challenge. We thrive on finding the answer. We hate disarray. It bothers us deep in our soul. W...
  2. SCCM OSD Basic troubleshooting
    SCCM 2007 OSD is a fantastic way to deploy operating systems, however, like most things SCCM issues can sometimes be difficult to resolve due to the sheer volume of logs to sift through and the dispe...
  3. Migrate Small Business Server 2003 to Exchange 2010 and Windows 2008 R2
    This guide is intended to provide step by step instructions on how to migrate from Small Business Server 2003 to Windows 2008 R2 with Exchange 2010. For this migration to work you will need the fo...
  4. Create a Win7 Gadget
    This article shows you how to create a simple "Gadget" -- a sort of mini-application supported by Windows 7 and Vista. Gadgets can be dropped anywhere on the desktop to provide instant information, ...
  5. Outlook continually prompting for username and password
    There have been a lot of questions recently regarding Outlook prompting for a username and password whilst using Exchange 2007. There are a few reasons why this would happen and I will try to cover t...
  6. Backup Exchange 2010 Information Store using Windows Backup
    There seems to be quite a lot of confusion around the ability to backup Exchange 2010 using the built in Windows Backup feature. This stems from the omission of this feature prior to Exchange 2007 s...

Cloud Class Webinars

  1. Avoiding Bugs in Microsoft Access
    Alison Balter takes and in-depth look at avoiding bugs in Access. In this webinar you will learn about using the immediate window to debug your applications, invoking the debugger, using breakpoints to troubleshoot, stepping through code, setting the next statement to execute, ...
  2. Top 10 Best New Features in Visio 2010
    Scott Helmers gives live demonstrations of the top 10 new features in Visio 2010. This webinar will teach you how to create compelling diagrams by adding shapes to the page with a single click, linking the shapes in a diagram to data in Excel (or SQL Server, or SharePoint), ...
  3. IT Consultant Business Secrets Revealed
    Michael Munger, Experts Exchange tech pro and IT consultant, pulls back the curtain on his very successful businesses and answers question on every IT consultant and business owner should know about. He shares secrets on what he did to solve the 5 most common problems in IT, ...
  4. Disaster Recovery and Business Continuity
    Quest CTO, Mike Billon, gives an overview of the steps involved in building a dunamic disaster recovery plan. Through case studies and an examination of software/hardware tooles for monitoring and testing, you'll gain a better understandin of where you are, where you want ...
  5. Organize Your Visio Diagrams with Containers and Lists
    Scott Helmers uses cross functional flowcharts, wireframe diagrams, data graphic legends and seating charts to teach you: how to ustilize all three new structured diagram components in Visio 2010, the best practices for organizeing shapes in previous version of Visio, how to organize ...
  6. How to Us Objects, Properties, Events and Methods in Microsoft Access
    Alison Dalter gives an in-depbth look at objects, properties, events and methods in Microsoft Access. In this webinar you will learn about using the object browser, referring to objects, working with properties and methods, working with object variables, understanding the ...

Join the Community

Give a Little. Get a Lot.

Join the community of experts here and help other tech pros by answering question in your area of expertise. You can earn FREE access to all Experts Exchange's premium features and resources.

Join the Community

Answers

 

by: ciulyPosted on 2009-01-04 at 12:28:44ID: 23291228

call the flush method. you'll need to upgrade your FPC to 2.2.2 to support that ;)

but I'm not entirely sure it's a flushing issue. the OS and the hdd should handle the buffering/caching just fine to boost speed not to slow things down.
flushing things will only go past those optimizations and caching/buffering and will normaly have a slowing effect.
the problem may lay elsewhere.

 

by: zakiwiPosted on 2009-01-04 at 12:34:34ID: 23291243

How do I call the flush method.  It wants a text file as input.

I accept your comments about the problem perhaps being elsewhere ... where would you look.  When the program breaks, it does not get out of the above loop so I get the error message every 500 ms

Thanks

 

by: ciulyPosted on 2009-01-04 at 12:44:01ID: 23291270

that is the flush PROCEDURE. only classes have methods. you use it like f:tfilestream; f.flush;

I would first make sure that all my resources are protected. generally speaking:

create resource
try  
  use reasource
finally
  destroy resource
end;

if I need a try/except there, I wrap the whoel thing in a try except. I never "optimize" the number of try's when it comes to resources.
resource can be anything: memory allocation, file opening, handle allocaiton, etc.

then I look for infinite cycles. even though usually a high CPU usage will notify of infinite loops, a high disk usage in case of a disk using application can also suggest the same thing, unless the high usage is "normal". which from what you tell me I take it's not. plus that since you mention not getting out of a loop... that kind of resembles an infinite loop. that's a bug, unless, again, it's normal. I rarely saw correct code which used infinite loops in commercial applications. I saw them all the time in networking applications in school projects but I am guessing this is not the case.

so, long story short:
- you need to see what happens when thigns go wrong
- and then, try to see in code why things went wrong doing what you noticed

what usually helps me to debug such applications is using a file log and logging critical places with critical values so that I can see a big picture of what's going on.
another thing that helps in such time-critical applications is using asserts. you know for a fact that some thigns must be in some ways. assert them. if they're not, you'll get an assertion failure and that is a problem: either your thinking is wrong, or the code is. in eitehr way, you are on the correct way to find the problem.

 

by: zakiwiPosted on 2009-01-04 at 12:54:29ID: 23291303

Mate ... there is no Flush method in the TFileStream object.

I'm using FPC 2.2.2 and Lanzarus 0.9.26 beta

Another point is that I just placed a 500 ms sleep after the file stream is destroyed  (within each processing itteration) , and disk access was notably less, BUT I still got the problem.  I think this confirms your first comment

 

by: zakiwiPosted on 2009-01-04 at 13:32:10ID: 23291488

Thank you.  You pointed me in the right direction.  The error was infact elsewhere.

In short, I placed a counter and found that the program was breaking after a certain number of itterations and that lead me to check my file handles, and there was a leak in a FindFirst() procedure.

Cheers and thanks

Zakiwi

 

by: ciulyPosted on 2009-01-04 at 14:20:52ID: 23291681

>> Mate ... there is no Flush method in the TFileStream object.

there is. download latest FPC and it's there. I checked BEFORE posting. if you don't want to waste time downloading, check the docs: http://www.freepascal.org/docs-html/rtl/objects/tstream.html

so, B grade is not acceptable in this situation.
1) I answered initial question for flush, correctly.
2) I pointed you in the right direction, which is kind of the only thing anybody could have done without having access to the faulty code. and in the end, I was indeed right: a resource was created and not destroyed, which was my first assumtion.

please ask mdoerators to reopen and regrade. thanks.

 

by: ciulyPosted on 2009-01-11 at 15:01:22ID: 23350121

thanks whackamod

20120131-EE-VQP-002

3 Ways to Join

30-Day Free Trial

The Experts

98% positive feedback on 31,087 answers since March 2000. angeliii is a Microsoft Most Valuable Professional for his work with MS SQL Server & Develoment.

He has also proven his knowledge of Visual Basic Programming, PHP Scripting and Oracle Databases.

The Experts

97% positive feedback on 10,752 answers since July 2000. lrmoore has more than 18 years experience in the networking industry.

The six-time Mircosoft MVPs specialties include firewalls, virtual private networking, and network management.

Testimonials

"...and excellent source for support... Kind of like having your very own IT dept." Electriciansnet

Testimonials

"I was apprehensive at signing up at first. However... it has already made my life as an IT administrator much easier." JaCrews

Testimonials

"WOW! You guys have great, active, and knowledgeable people on here." moore50

Business Clients

Business Clients

In the Press

"If you’ve got a question... Experts Exchange can supply an answer.”

In the Press

"...an invaluable aid for both IT professionals and those who require tech support."

In the Press

"where IT professionals provide quick answers on just about any topic"

Business Account Plans

Loading Advertisement...