History:

Multiple processes are appending to and updating multiple files. "\n" line/record delimiter. The hardest hit files were being truncated, sometimes in the middle of a line. Had been using flock() per numerous examples, but didn't work. I suspect something to do with locks in user space.

Partial solutions:

Switched to using DBI::CSV and I wrote a daemon with example (verbatim) from IO::Select using IO::Socket with a simple protocol to arbitrate file access. Sockets are being read and printed using "\n" to complete:

Process requested a socket ==> Daemon accepted socket request
Process asked for access ==> Daemon accepted request - via socket
Daemon granted access ==> Process accepted access - via socket
Process accessed file
Process gave up access ==> Daemon accepted - via socket
Process and Daemon moved on

Results:

Immediate results were positive. It took a while before I started to find "signs" of corruption which couldn't be verified - some data seemed inconsistent, though there could be a perfectly reasonable explanation for it. Then I found some log files (should be simple appends) that had portions of lines mushed together, and some lines that had embedded "\n" where the processes couldn't be generating it.

Question:

Is there some way to ensure that the DBI::CSV actually locks files for update, or some way to make sure any write buffers it uses are being flushed with every write/update?

I can't think of anything else that may be allowing processes to clobber each other's file updates.

Thanks.

In reply to DBI::CSV file locking? by blackrat

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