undefined | Better HN

0 pointsrewqfdsa10y ago0 comments

> What is hard about making signals cooperate?

Library A wants to handle SIGSEGV for memory mapping X. Library B wants to handle SIGSEGV for memory mapping Y. Which of them calls sigaction? What if both do? What if then unload one of the libraries?

Windows handles this interaction sanely. Sigaction does not.

> raise() is supported on Windows, but kill()

Windows splits the jobs of signals into structured exceptions and APCs. You can definitely send an APC to another thread: https://msdn.microsoft.com/en-us/library/windows/desktop/ms6...

0 comments

fulafel10y ago

It's actually alarmingly common for Windows C/C++ apps to paper over crashes with SEH try { } catch (segfault) { /* seems to work */ } this way. Even Microsoft's own apps used to do it, maybe they still do. You run into this when running random apps under a debugger.

silon710y ago

There's nothing structured about core dumps. Better to do nothing so the developer can see a clean core dump.

ratboy66610y ago

sigaction() returns the old action. This permits chaining of the actions. Specifically for SIGSEGV, if Library B does not want the signal, it can invoke Library A (without caring what it is). Similarily, A can invoke B. "Unloading" cannot be done, unless you are aware of the load order. This is a general issue -- dlclose() is reference counted, and you wouldn't know if it actually unloaded the library.

useerup10y ago

> Unloading" cannot be done, unless you are aware of the load order. This is a general issue -- dlclose() is reference counted, and you wouldn't know if it actually unloaded the library.

Yup. Which is exactly why Windows is more sane: No chaining, "unloading" (i.e. unsubscribing) can be done robustly. In the absence of a mechanism like SEH on Linux, signals are (mis)used. Signals are a crude, unstructured way of handling internal termination.

j / k navigate · click thread line to collapse