Reading and writing in concurrent threads

[Brainiac]

Hi everybody.

I'm developing an application with the following schema:

main thread:
   - Creates another thread that periodically reads from DB and updates a shared object that is passed by reference.
   - Starts a UNIX socket listening loop.
   - Creates another thread when a new connection arrives. Let's call it working thread.

working thread:
   - Receives by reference the same shared object that the DB thread receives.
   - Reads and writes to the shared object. 

The problem here is that I don't really know where add some MUTEX to prevent race conditions. Actually I use MUTEX in the working thread, always when I'm writing to the shared object. I think I must use the same MUTEX when updating the shared object in the DB thread. But, what happens when the working thread reads from the shared object? Must I use the MUTEX when reading?

Besides these questions, the application crashes sometimes with a SIGSEGV. Debugging with gdb I see that this happens, apparently randomly, when reading the object in the working thread...

Any help with these problem?

Best regards.

[helios]

Must I use the MUTEX when reading?

Yes.

[Brainiac]

Do you think that the SIGSEGV is related to the reads that are done without MUTEX?

[helios]

Probably, yes.