I am still having this issue. I've managed to narrow down what is happening some. The problem is my data is not actually being written all the way to disk. I now have a repeatable proven method to reproduce the issue. Here is the sequence.
In my freepascal console application, I create the file Assign file Rewrite file Writeln file Writeln file Writeln file ... Flush file Close file I then immediately read back the file, and all is good. I even look at the file with notepad++ to see that the data is correct.... and it is fine. If I then power off the test computer (not doing a correct windows shutdown, this simulates an unattended power failure) when it boots back up, my file has the correct date and time and the correct length, hovever the contents of the file is a string of $00 with no other characters, no carriage returns and no linefeeds, however the number of $00s is EXACTLY how many bytes the file should have been. It's like the file was allocated but data not actually written to disk yet... but I thought Close (file) was supposed to do that. I think I am dealing with some kind of disk caching going on here, but I'm not sure how to force my files to commit all the way to disk. I should note that these systems are all using Samsung SSDs in them, perhaps there is some SSD weirdness going on? I also notice it's not just this one file that is affected, but EVERY SINGLE FILE I create with freepascal, this is the only one I notice because the other ones are all work files that end up being re-created every time I run my program, but I checked them all and they are all exactly the same.. correct lengths but all data is a string of 00s I'm thinking of just disabling all write behind caching in windows and on the SSD if I can figure it out, it's not needed anyway anymore because SSDs are way more than fast enough, and I would rather wait for my data to be written NOW instead of it NOT getting written later!! The problem with solving this by disabling write caching is that I can never be sure that this was done. So I would like to find a real solution that would force my files all the way to disk on my own without depending on the system being configured a certain way. I really need these tiny files to survive power failures. Thanks for any advice on how to do this James -----Original Message----- From: fpc-pascal-boun...@lists.freepascal.org [mailto:fpc-pascal-boun...@lists.freepascal.org] On Behalf Of James Richters Sent: Friday, February 24, 2017 1:53 PM To: 'FPC-Pascal users discussions' <fpc-pascal@lists.freepascal.org> Subject: Re: [fpc-pascal] FreePascal Windows - Force files to write to disk Thanks for the advice everyone. It is very much appreciated. I have been working on a combination of ideas here. Currently I am doing an MD5sum of a string created from all my variables concatenated together and writing that as the second to the last line of the file, I also am writing some fixed text at the beginning and end of the file as suggested so I can check for variables being overwritten in memory, great idea! I am then reading the file back to verify it has written properly, making a backup, checking that, and also using ioresults as below. I will probably rename the file as well, and exclude it from virus checkers. When I read the file I can verify the MD5sum and if that test fails, I'll just automatically try the backup, If that also fails the MD5sum I'll notify the user. Thanks again for all the help James -----Original Message----- From: fpc-pascal-boun...@lists.freepascal.org [mailto:fpc-pascal-boun...@lists.freepascal.org] On Behalf Of Klaus Hartnegg Sent: Thursday, February 23, 2017 6:33 AM To: fpc-pascal@lists.freepascal.org Subject: Re: [fpc-pascal] FreePascal Windows - Force files to write to disk Am 21.02.2017 um 22:12 schrieb James Richters: > Assign(BitFile,'BitSave.pax'); {$I-} > ReWrite(BitFile); if ioresult <> 0 then writeln ('error opening pax file'); > WriteLn(BitFile,XADJ:1:8); > WriteLn(BitFile,YADJ:1:8); > WriteLn(BitFile,ZADJ:1:8); > WriteLn(BitFile,WADJ:1:8); > WriteLn(BitFile,AADJ:1:8); > WriteLn(BitFile,TADJ:1:8); > WriteLn(BitFile,VADJ:1:8); > WriteLn(BitFile,UADJ:1:8); > WriteLn(BitFile,CurrentTool); > WriteLn(Bitfile,P_Value[4]); writeln (bitfile, 'EOF'); if ioresult <> 0 then writeln ('error writing pax file'); > Close(BitFile); if ioresult <> 0 then writeln ('error closing pax file'); {$I+} This writes something at the end of the file that does not come from a variable. Next time the error happens, you can check if that is present. Then your variables were overwritten in memory. Also it checks for errors. And I would disable antivirus or at least tell it to not scan this file. _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal _______________________________________________ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
