freeing memory inside a signal handler

Question

I am writing an API that uses sockets. In the API, I allocate memory for various items. I want to make sure I close the sockets and free the memory in case there is a signal such as Ctrl-C. In researching this, it appears free() is not on the safe function list (man 7 signal) thus, I can't free the memory inside a signal handler. I can close the socket just fine though. Does any have any thoughts on how I can free the memory? Thank you in advance for your time.

Answer 1

Alternatively, don't catch the signal and just let the OS handle the cleanup as it's going to do during process cleanup anyway. You're not releasing any resources that aren't tied directly to the process, so there's no particular need to manually release them.

Answer 2

One technique (others exist too):

1. Have your program run a main processing loop.
2. Have your main processing loop check a flag to see if it should "keep running".
3. Have your signal handler simply set the "keep running" flag to false, but not otherwise terminate the program.
4. Have your main processing loop do the memory cleanup prior to exiting.

This has the benefit of placing both the allocation and de-allocation in blocks of code which are called with a known sequence. Doing so can be a godsend when dealing with webs of interrelated objects, and there is not going to be race condition between two processing flows trying to mess with the same object.