Thread: SYnchronize read & write of a cache file

I need to implement the following module using C programming on both Solaris and Windows.

1. The module will be used by multiple processes;
2. The module calls an existing batch file from time to time;
3. The batch file provides some output information that will be parsed by its caller;

It may take a few seconds for the batch file to complete its execution. Hence to speed up, I need to implement a caching mechanism for the outputs of the batch file. This way the first caller of the batch file writes the outputs to a cache file, the following caller can then just open the cache file to get the information. I will also use a timeout parameter to decide if the cached information is expired and if so the batch file will be re-executed to refresh the cache.

My question is, how should I synchronize the read and write operation of the cache file? Read/write locks, semaphore, or something else?

Thanks!

Read/Write lock sounds good to me. That way you can have multiple readers but only one writer.

gg

Can you please provide more details regarding to the implementation of read/write lock? For example, should I use two locks or just use one lock and access it bydifferent mode? What are the specific C function names? Please note the lock(s) is used by multiple processes instead of threads.

You could use a couple of semaphores to implement a read/write lock. In *nix, there are usually 2 API's to choose from...

Semaphores in the SVR4 specification come from <sys/sem.h> and include the functions semctl(), semget(), and semop().

The Single Unix Specification, aka POSIX, has their own semaphore api from <semaphore.h> and include the functions sem_init(), sem_post(), sem_wait(), sem_destroy(), etc...

For implemented a read/write lock - the concept is covered in this thread: http://cboard.cprogramming.com/showt...php?t=95848#10

gg

Thanks!