[io] Prevent losing data due to SIGTERM (under Unix)

[ferdymercury]

This Pull request:

Changes or fixes:

Fixes #13300

• I tested this locally on Ubu22 and it works fine.
• I do not know how to properly test it using GTEST, I only found test_polling.cxx doing something like that but it looked too complicated, so I ended up simplifying.
• I do not know if Windows must catch SIGTERM somewhere else @bellenot ?

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    20 files      20 suites   4d 6h 27m 36s ⏱️
 3 016 tests  3 015 ✅ 0 💤 1 ❌
58 726 runs  58 725 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit beb694c.

♻️ This comment has been updated with latest results.

[bellenot]

@ferdymercury The SIGILL and SIGTERM signals aren't generated under Windows. They're included for ANSI compatibility. See the signal reference

[dpiparo]

Let's have a look to the tests once again

[pcanal]

If I understood correctly, this would mean that after code similar to:

root [] TFile f(filename, RECREATE);
root [] do_stuff();
root [] if (all_is_well) f.Write();

We have a different behavior if the user does:

root [] .q

and

send SIGTERM

Where the former does not write the file while the later would now write the file.

[ferdymercury]

Yes.