Re: [fpc-pascal] File locking/protection in Linux
On Wed, 2 Nov 2005, Antal wrote: How can be avoided in Linux the file corruption due to simultaneous write access from two different process? Or how can it be avoided to access the same file by two different process? I experienced a few (but painful) data loss due to this problem, and I'm unable to solve the problem. You can use the fpflock call (unit 'unix') to lock (parts of) a file. But be aware that BOTH processes must use this mechanism; File locking is optional on Linux. Nothing prevents a third process from using the file without locks. Michael. ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] File locking/protection in Linux
On 11/2/05, Michael Van Canneyt <[EMAIL PROTECTED]> wrote: > On Wed, 2 Nov 2005, Antal wrote: > > > How can be avoided in Linux the file corruption due to simultaneous write > > access from two different process? > > Nothing prevents a third process from using the file without locks. that was what i thought too. but that link i posted seemed to imply that, if you mounted the filesystem with an extra flag, that the kernel would cause any regular process to wait for access to files, if those files had been "flocked" by any one process, so it then only takes 1 process using the "flock" calls to get exclusive access. from the link : "In these cases, you can enforce locking at the kernel level with mandatory locks. Mandatory locking is implemented on a file-by-file basis. When a program attempts to lock a file with lockf or fcntl that has mandatory locking set, the kernel will prevent all other programs from accessing the file.[1] Processes which use flock will not trigger a mandatory lock." > > Michael. Tony ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
[fpc-pascal] base64 decoding
I use Free Pascal for programming a small utility for two quite busy Mac OS X mail server (Postfix|CRM114|ANOMY|Cyrus) which prepares and preselects incoming mails (filtering or leraning) for the statistical mail filter CRM114. Today, I managed to use the fcl base64 classes for decoding respective parts of the piped through e-mails. However, it took me some time to get it to work, and I have still some doubts if the base64 decoding class is stable enough for unattended operation on a busy mail server. Possibly somebody has more experience with the fcl base64 classes than I have, and hopefully can destroy my doubts. Base64 encoded parts of e-mails usually include line breaks (LF at Mac OS X Server) every 76 characters. When I write these LF into the TMemoryStream which is passed to TBase64DecodingStream, then the decoder freezes during the read beyond the first line break. If I pass through CRLF or only CR instead of LF then it freezes also - it seems that the decoder is caught into an endless loop. The obvious workaround is not to write the line breaks into the TMemoryStream. Actually, I check whether the input char belongs to the base64 character set before it is written to the TMemoryStream - also CR/LF is filtered out by this way. if ch in ['A'..'Z', 'a'..'z', '0'..'9', '+', '/', '='] then base64Stream.WriteByte(Char(ch)); My question here is, whether this catches every malformed base64 code, so that the decoder does not freeze. Another problem was, that TBase64DecodingStream.EOF() does not indicate properly the end of the decoded stream. Instead, I was forced to use the "try read() except on EStreamError" sequence for the eof indication. My question here is, whether this works in any case. Again, I am a little bit afraid, that the decoder might be caught into an endless loop. Many thanks for any helpful comments. Best regards Rolf ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: [fpc-pascal] base64 decoding
On Wednesday 02 November 2005 22:06, Dr. Rolf Jansen wrote: > Today, I managed to use the fcl base64 classes for decoding > respective parts of the piped through e-mails. However, it took me > some time to get it to work, and I have still some doubts if the > base64 decoding class is stable enough for unattended operation on a > busy mail server. Sort of the same problem struck me yesterday, too, but with streams which are perfectly valid containing only base64-chars. // somehow the current implementation of base64 decoding stream is // broken, it sometimes raise StreamReadError instead of decoding // the values correctly (if you feed $000102...7A7B7C into it, // it stops just before decoding $7C, or try feeding a constant // stream of $7D into it, it will stop after the first byte // decoded) Because I need this for XML-RPC server/client stuff, and thus I need the HTTP-capabilities of it anyway, I (temporarily?) switched to Synapse's SynaCode unit. AFAICS it doesn't have any problems with invalid base64 chars, it simply ignores them. Lukas, correct me if I'm wrong. Currently I can't neither file a bug report nor check the current svn if it's fixed already, because I don't have access to any of *.freepascal.org. :-( Someone's blocking me and I haven't figured out why and who yet. HTH, Vinzent. -- public key: http://www.t-domaingrabbing.ch/publickey.asc pgpG7FAFe3pKJ.pgp Description: signature ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
