Handle two programs writing to the same file in C++? Help?

[natxie]

Hi, how to synchronize two cgi programs called
from browser, and write data to the same file
at the same time in C++?

Thank you very much,

Natxie

[Banti]

WHY??? And how are you at Shared Memory?

Banti

[natxie]

Hi, here's the more info:

It's a cgi prgram which read a file, and change some data in it, then write to the same file.
There's a possibility that two users access the
same cgi program at the same time, then write to
the same file at the same time, that caused
problem.
Is there's a way to handle it in C++?

Thanks,

Natxie

[qball]

concurrency is your problem. you have more than one 'user' trying to write to the same file at the same time, not good.

Now is your question about CGI or C++?

Either way, minimize your file IO. Only write to file when absolutely necessary, then open, write, close as fast as possible.

Why are you using file? Sounds like you need a DB.

[^hyd^]

I'm pretty sure c++ lets you lock your file as well, lock -> write/read -> unlock, but you might have already tried that. Not sure if it would do much or not, but I believe thats what the intention of the lock is! (mebbe, mebbe not!)

...you can look into semaphors if you want also!!