Re[2]: [Declude.JunkMail] Log Corruption
On Tuesday, March 1, 2005, 5:38:54 PM, Darrell wrote: Dsic I though Pete had some locking mechanism built in to prevent overlapping. Dsic Pete? Yes. This is it. (quite a lot of locking actually) This is a pet peeve of mine so I'm going to go just slightly off topic - it might help someone else out there writing code like this... There are a number of things in Win32 land that are not atomic like they should be. (Atomic meaning - they complete all at once before anything else can happen.) One of these that caused a lot of extra work in SNF peer-server code is rename(). The other is appended writes to a file. As a result, it is possible for more than one thread to believe it has renamed a single file successfully - which is supposed to be impossible. Thread A tries to rename file JOB.QUE to JOB.AAA and succeeds. Thread B tries to rename file JOB.QUE to JOB.BBB and succeeds!!! The actual file name at the end - flip a coin and pick one - JOB.BBB or JOB.AAA. Appended writes work the same way. Thread A opens a file for Append and writes Thread A stuff and only thread A stuff so there!\n Thread B opens the same file for Append and writes: Thread B, thread B, what a silly thread I B!\n Both writes succeed happily. Unfortunate sleep deprived programmer sure that he is going stark raving mad opens up the file and sees: Thread A stufead B, what a silly th\n I B! there... where ... is following on to some other unrelated log entry... (sigh) Luckily, it seems that creating a file is atomic, so there is a way out. This is what I use for some simple inter-process locking (that, by the way, is cross-platform [posix] compatible): open(LockName.c_str(),O_WRONLY|O_CREAT|O_EXCL); --- The actual code I use for locking is bigger than this of course. I'm attaching an excerpt from logger.cpp that takes care of it. Hope this helps, _M win32lock.cpp Description: Binary data
Re[2]: [Declude.JunkMail] Log Corruption
On Tuesday, March 1, 2005, 5:48:17 PM, Andrew wrote: CA (Pete isn't here much) :-( I do usually lurk though... I'll try to post more often... ;-) _M --- [This E-mail was scanned for viruses by Declude Virus (http://www.declude.com)] --- This E-mail came from the Declude.JunkMail mailing list. To unsubscribe, just send an E-mail to [EMAIL PROTECTED], and type unsubscribe Declude.JunkMail. The archives can be found at http://www.mail-archive.com.
Re[2]: [Declude.JunkMail] Log Corruption
On Tuesday, March 1, 2005, 7:14:31 PM, Darin wrote: DC I disagree with the struggling server logic. We saw the log corruption in a DC test environment a year ago that had minimal traffic, say a couple thousand DC messages a day. It was a dual 1.4GHz processor with 1 GB RAM and 10k RPM DC SCSI drives. Load was only about 1-5% during testing. Heavier loads will cause more processes to collide and so log corruption is likely to be more pronounced in those situations. _M --- [This E-mail was scanned for viruses by Declude Virus (http://www.declude.com)] --- This E-mail came from the Declude.JunkMail mailing list. To unsubscribe, just send an E-mail to [EMAIL PROTECTED], and type unsubscribe Declude.JunkMail. The archives can be found at http://www.mail-archive.com.
Re: Re[2]: [Declude.JunkMail] Log Corruption
Correct. What I was saying I disagreed with was the concept that it only occurred on struggling servers. This test machine was very lightly loaded and we saw log corruption. Darin. - Original Message - From: Pete McNeil [EMAIL PROTECTED] To: Darin Cox Declude.JunkMail@declude.com Sent: Tuesday, March 01, 2005 7:30 PM Subject: Re[2]: [Declude.JunkMail] Log Corruption On Tuesday, March 1, 2005, 7:14:31 PM, Darin wrote: DC I disagree with the struggling server logic. We saw the log corruption in a DC test environment a year ago that had minimal traffic, say a couple thousand DC messages a day. It was a dual 1.4GHz processor with 1 GB RAM and 10k RPM DC SCSI drives. Load was only about 1-5% during testing. Heavier loads will cause more processes to collide and so log corruption is likely to be more pronounced in those situations. _M --- [This E-mail was scanned for viruses by Declude Virus (http://www.declude.com)] --- This E-mail came from the Declude.JunkMail mailing list. To unsubscribe, just send an E-mail to [EMAIL PROTECTED], and type unsubscribe Declude.JunkMail. The archives can be found at http://www.mail-archive.com. --- [This E-mail was scanned for viruses by Declude Virus (http://www.declude.com)] --- This E-mail came from the Declude.JunkMail mailing list. To unsubscribe, just send an E-mail to [EMAIL PROTECTED], and type unsubscribe Declude.JunkMail. The archives can be found at http://www.mail-archive.com.
