it galls me that I don't understand how to get a signal handler in a thread to work

The short answer is that they don't work in threads. Signals are sent to the process, not individual threads within it. The salient part of the relevant documentation for linux reads:

A signal's disposition within a process's context defines what action the system will take on behalf of the process when a signal is delivered. All threads and LWPs (lightweight processes) within a process share the signal disposition, which is processwide and cannot be unique among threads within the same process.

That said, threads belatedly acquired some additions that attempt to allow "inter-thread signalling", but in my limited experience of trying to use them, they are essentially useless, as they won't actually interrupt anything -- you have to poll to see if they have been received.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^5: Interrupting a blocking read (Linux::Inotify2) with a signal handler within a thread by BrowserUk
in thread Interrupting a blocking read (Linux::Inotify2) with a signal handler within a thread by clueless newbie

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