flockfile() and funlockfile() question

[qednick]

Hi again all,

back to my conversion to c/c++ cgi scripts on UNIX system... I want to know if the functions [tt]flockfile()[/tt] and [tt]funlockfile()[/tt] are sufficient to prevent corruption when writing to a file on the UNIX web server.

For example, if I was to write to a file using PERL, I would use the function [tt]flock()[/tt] to prevent any other instances of the same script from writing to the file at the same time and therefore corrupting it.

Any info would be appreciated...

Thanks!

^{programmer (prog'ram'er), n A hot-headed, anorak wearing, pimple-faced computer geek.}​

 

[jstreich]

I am unfamiliar with said functions, but I do know that you can use a semiphore and memory mapping to achieve the sharing of resources without data corruption. The memorymapping would let you read/write to the file simply as if the file were an array of charictors. The semiphore would achieve a ATOMIC operation (test-n-set) of a flag to tell other users of the state, it would also queue up the other users for you, fo you don't bur nclock cycles with a while loop arround the attempt to read/write.

Granted that these are a little more involved than simple function calls, but there is also a lot more power to them.

There are some really good resources about memory mapping and semiphores at: http://www.ecst.csuchico.edu/~beej/guide/ipc/