[gpderetta]

You can sort of emulate that with pthread_kill and EINTR but you need to control all code that can call interruptable sys calls to correctly return without retry (or longjmp/throw from the signal handler, but then we are back in phtread_cancel territory)

[AndyKelley]

There's a second problem here that musl also solves. If the signal is delivered in between checking for cancelation and the syscall machine code instruction, the interrupt is missed. This can cause a deadlock if the syscall was going to wait indefinitely and the application relies on cancelation for interruption.

Musl solves this problem by inspecting the program counter in the interrupt handler and checking if it falls specifically in that range, and if so, modifying registers such that when it returns from the signal, it returns to instructions that cause ECANCELED to be returned.

Blew my mind when I learned this last month.

[Veserv]

Introspection windows from a interrupting context are a neat technique. You can use it to implement “atomic transaction” guarantees for the interruptee as long as you control all potential interrupters. You can also implement “non-interruption” sections and bailout logic.

[cryptonector]

In particular you need to control the signal handlers. You can't do that easily in a library.