forward signals

[Antoine Martin]

Follow up from #1350: we now create a fake process for each server pid and we will receive signals sent by pagers and window managers, we should forward those to the real server-side process and let it decide what to do with it.

This will require:

• a new capability: "window.signals"
• a new server message: ["window-signal", wid, signal] (we send the wid and let the server find the real pid)

[Antoine Martin]

See also #1702

[Antoine Martin]

Support for SIGINT and SIGTERM forwarding added in r17608, with one important limitation: the watcher process exits when it receives any signal, so this can only be used once per watcher process.

Still TODO: keep watcher running after handling signals and communicate with parent process using stdin / stdout

[Antoine Martin]

Done in r17609 + r17616.
The signals we now forward are: SIGINT, SIGTERM, SIGQUIT, SIGCONT, SIGUSR1, SIGUSR2. (this can be changed using the XPRA_WINDOW_SIGNALS env var)

@maxmylyn: mostly a FYI, you can send a signal to the pid of an xpra window and it will be forwarded to the server process.

[J. Max Mena]

Neat. Noted. Closing.

[Antoine Martin]

Caused a regression and now disabled for python2: #2025.

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/1671