Pthread exit

FATAL: exception not rethrown
A 2019-12-20T12:39:03.230677552 @140313816094464 Abort signal. (SIGABRT):
 #00 0x00007F9D626EDF20 +257824 [/lib/x86_64-linux-gnu/libc.so.6]
 #01 0x00007F9D626EDE97 gsignal+199 [/lib/x86_64-linux-gnu/libc.so.6]
 #02 0x00007F9D626EF801 abort+321 [/lib/x86_64-linux-gnu/libc.so.6]
 #03 0x00007F9D627385E5 +562661 [/lib/x86_64-linux-gnu/libc.so.6]
 #04 0x00007F9D6273892A +563498 [/lib/x86_64-linux-gnu/libc.so.6]
 #05 0x00007F9D66078ED0 __pthread_unwind+0 [/lib/x86_64-linux-gnu/libpthread.so.0]
 #06 0x00007F9D63B732FD libtbag::thread::__global_uv_thread_cb__(void*)+223 [/home/user/Project/tbag/cmake-build-debug/libtbag.so.0]
 #07 0x00007F9D6606F6DB +30427 [/lib/x86_64-linux-gnu/libpthread.so.0]
 #08 0x00007F9D627D088F clone+63 [/lib/x86_64-linux-gnu/libc.so.6]

Sorry to be the bearer of bad news but it is very hard to get pthread_cancel to work properly in C++ in Linux.

The reason is that the pthread_cancel method implementation in Linux is absolutely horrid. In particular it causes an exception (abi::__forced_unwind as of the time I'm writing this) to be thrown. This probably is fine in a C program, but in C++ it makes it very difficult to handle the thread cancellation properly. In particular if you have any code that eats exceptions (such as catch (...)) this internal exception will handled and not passed up the stack the way it needs to be. In this case you will see the error message that you are seeing.

That said, I don't see what in your code would be "eating" this exception, but I suspect it is something of that nature that is causing the problem.

In your particular example this is easy to work around by using a flag or something similar to note when you want to exit and not call pthread_cancel. Unfortunately that makes sleep more complex (you need to call it multiple times with small intervals in order to check the flag) and calls to accept nearly impossible (you have to make a connection to the port from another thread or process to force accept to exit so you can check the variable). There is a long discussion on the problems with thread cancellation in general ([https://lwn.net/Articles/683118/ This is why we can't have safe cancellation points]) but given that macOS (and presumably other non-Linux "unixes") seem to handle it well, I really think that the Linux implementation could be done better. But until that is done, pthread_cancel will remain very difficult to use.