Segfault logic with two threads

Question

I have an application with main thread and additional (detached) process created in it. In that process we are running network server which sends logs from queue through the network.

The question is: is it possible to do something in segfault handler to wait/finish for sending that log queue. So I want almost 100% delivery of that queue.

Answer 1

While it is possible to write a segfault handler, I highly recommend against it. First off, it's very easy to get your program into a "won't terminate" state due to a segfault in the segfault handler.

Second, as dan3 mentions, the memory of the process is likely in a corrupt state, making it hard to know what will and won't work.

Finally, you lose the opportunity to use the coredump from the process to help track down the problem.

While it's not recommended, it is possible.

My recommendation is to write a small program that avoids memory allocation and the use of pointers as much as possible. Perhaps create buffers as global arrays and only ever access them with limited code that can be reviewed by several skilled developers and tested thoroughly (stress testing is great here). Keep in mind, though, that the message could still get lost by the sender or receiver if they crash, so it may not be worth the effort.

By the way - when Netscape first wrote a version of their browser for Linux, I ran it and it kept getting into a locked-up state. Using the strace program, I quickly found that it was in an infinite segfault loop. Very frustrating, and leading to almost 100% cpu wasted.

Answer 2

You can wait() for a process and pthread_wait() for a thread to finish (you didn't specify clearly which one you use).

Remember that if you are in segfault handler, your memory is messed up (avoid malloc() and free()) and your FILE * could also be borked.