File Locking

I have a bit of a problem wrapping my head around some of it.

All examples I see, have you use an exclusive file lock when writing.

And a shared file lock when reading.

What happens if I don't use a shared file lock if I'm only reading a file?

Undefined behavior if someone else writes at the same time if you don't use a lock at all, or asshole behavior on your part if someone else tries to read at the same time if you use an exclusive lock.

That was a hard one. For your next question, ask what the difference between a thread and a process is and we can all be in high school again.

Really?

Okay. Reading doesn't alter data, so shared locks are cool here no problems arise from multiple readers.

Writing does alter the data. If you don't get an exclusive lock then you can get corrupt data in the file, or at least into a reader.

A lot of locks are purely voluntary, so um, yeah. Don't assume anything outside your app is going to play by the rules, unless you know you're in an environment where obeying the locking facility you have chosen is enforced.

I'm sure wikipedia has something interesting to say on the matter: http://en.wikipedia.org/wiki/File_locking but I can't be arsed to read it.

>>3
Yeah, because everybody in /prog/ is a working ENTERPRISE programmer.

No wait, you actually think the only people who should be allowed to post here are those kinds of persons.

/prog/tip: If you ever find yourself in a situation where file locking seems like a good idea, you should seriously reconsider your design.

>>5
/prog/ is not /helpmewithmyhighschoolhomework/. You're looking for /pr/.

>>5
You're an idiot. What the locks do is right there in the name. It doesn't take a huge amount of experience to read.

>>5
I program mostly as a hobby. I make a living from restoring and fixing up old houses, especially plaster.

1. Open every file in your system with full read/write lock.
2. ???
3. PROFIT

>>9
this made me wtf.
that's the last hobby i would expect a construction worker to have.

>>11
Why? Fixing old houses, especially plaster, is very similar to programming, except that you can do the latter while sitting in a comfortable chair, not being covered with plaster dust etc.

>>12
How do you simulate a Turing-complete machine by fixing a house?

>>13
You don't.

>>13
I did this by buying a house next to a theoretically infinite river and some ducks.

>>15
if you lived next to a river, would it be legal to kill and eat the ducks inhabiting it?

LOCK MY ANUS

This thread had been semaphored.  You can't reply to it right now.

>>18
V()

>>19
Exception in thread “1260941086”
 prog.util.ConcurrentModificationException

^{Back to /b/, ``GNAA Faggot''}

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