dlopen之后使用fork

Question

I used dlopen to load a dynamic link library (.so) in my program, called dlsym to get the address to a certain function foo .

Then I used fork and called foo in the sub-process, and used exit(0) to exit the sub-process. Till now, everything is alright.

And when I tried to fork and call foo again in the sub-process, I found that all data stored by static variables defined in foo was lost. I am sure that I didn't call functions like dlclose explicitly. So how can I prevent the data from disappearing?

Thanks a lot.

Answer 1

You want shared memory. See How to use shared memory with Linux in C for some introductory pointers. Be forewarned, however, that synchronization is tricky and you will probably end up wanting a higher-level abstraction, like message-passing or semaphores.

(Alternatively, maybe forking isn't the model you're looking for. Threads are literally the concept of having multiple execution paths using the same process-memory space...)

Answer 2

fork ing your program has the effect of duplicating its address space, including the storage for foo 's static locals. It's that copy that was initialized in the child process by the call to foo .

It is no surprise, then, that the original storage is unchanged, as you can see from the second fork and call to foo on a second copy of that uninitialized storage.