pthread_exit() in C++
Today I ran into an interesting problem that I would like to share. I am working on multi-threaded code in C++. Here’s what happened.
I started a thread that looks like this:
try {
do_something()
} catch (...) {
std::cout << "Got unknown exception" << std::endl;
}
The do_something() routine eventually called pthread_exit().
Once I ran this piece of code, I instantly got an unknown exception notification. Long story short, here’s what I found out.
When calling pthread_exit() in C++, it has to destruct all objects that has been created on stack. This process called stack unwinding and this is exactly what happens when you throw an exception. pthread_exit() utilizes this feature of C++ to cleanup before shutting down the thread for good.
To do that pthread_exit() throws some obscure exception and catches it right before ditching the thread. This way it cleans up all objects nicely. On the other hand, catching … becomes impossible.
If you are the programmer calling pthread_exit, then a simple workaround would be to use some per-thread bool, then just before calling pthread_exit set it to – say – true, and in your catch code check for it and re-throw if necesary, so that pthread library has nothing to complain about. Wraping it up in some nice function would make it easily workable.