CODEWITHSUNDEEP
algorithmcomputer-science
user1535147
user1535147

Reputation: 1475

Obtaining Dynamically Changing Log Files

Does the problem I am facing have some kind of a fancy name like "Dining philosophers problem" or "Josephus problem" etc etc? This is so that I can do some research on it.

I want to retrieve the latest log file in Windows. The log file will change its name to log.2, log.3, log.4 .....and so on when it is full(50MB let's say) and the incoming log will be inserted in log.1.

Now, I have a solution to this. I try to poll the server intermittently if the latest file (log.1) has any changes or not. However, I soon found out that the log.1 is changing to log.2 at an unpredictable time causing me to miss the log file (because I will only retrieve log.1 if log.1 has any changes in its' "Date Modified" properties).

I hope there is some kind of allegory I can give to make this easy to understand. The closest thing I can relate is that of a stroboscope freezing a fan with an unknown frequency giving the illusion of the fan is freezing but the fan has actually spin lot of time. You get the gist.

Thanks in advance.

Upvotes: 0

Views: 70

Answers (2)

Jim Mischel
Jim Mischel

Reputation: 134045

The solution will be to have your program keep track of the last modified dates for both files log.1 and log.2. When you poll, check log.2 for changes and then check log.1 for changes.

Most of the time, log.2 will not have changed. When it does, you read the updated data there, and then read the updated data in log.1. In code, it would look something like this:

DateTime log1ModifiedDate  // saved, and updated whenever it changes
DateTime log2ModifiedDate

if log2.DateModified != log2ModifiedDate
    Read and process data from log.2
    update log2ModifiedDate
if log1.DateModified != log1ModifiedDate
    Read and process data from log.1
    update log1ModifiedDate

I'm assuming that you poll often enough that log.1 won't have rolled over twice such that the file that used to be log.1 is now log.3. If you think that's likely to happen, you'll have to check log.3 as well as log.2 and log.1.

Another way to handle this in Windows is to implement file change notification, which will tell you whenever a file changes in a directory. Those notifications are delivered to your program asynchronously. So rather than polling, you respond to notifications. In .NET, you'd use FileSystemWatcher. With the Windows API, you'd use FindFirstChangeNotification and associated functions. This CodeProject article gives a decent example.

Upvotes: 3

user2746020
user2746020

Reputation: 67

Get file-list, sort it in decending order, take first file, read log lines!

Upvotes: 0

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