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If I’m writing a simple text log file from multiple processes, can they overwrite/corrupt each other’s entries?
(Basically, this question Is file append atomic in UNIX? but for Windows/NTFS.)
Even if append is atomic (which I don’t believe it is), it may not give you the results you want. For example, assuming a log includes a timestamp, it seems reasonable to expect more recent logs to be appended after older logs. With concurrency, this guarantee doesn’t hold – if multiple processes are waiting to write to the same file, any one of them might get the write lock – not just the oldest one waiting. Thus, logs can be written out of sequence.
If this is not desirable behaviour, you can avoid it by publishing logs entries from all processes to a shared queue, such as a named pipe. You then have a single process that writes from this queue to the log file. This avoids the conccurrency issues, ensures that logs are written in order, and works when file appends are not atomic, since the file is only written to directly by one process.