Mark Morgan Lloyd schrieb:
Sven Barth wrote:
On 16.02.2013 09:22, Mark Morgan Lloyd wrote:
On unix (Linux, Solaris etc.) is it possible to determine how a program
written using Lazarus is being terminated? Specifically, is there any
different behaviour when a kill signal arrives from a routine term
signal, and is a title-bar close button simply a term signal?
SIGTERM can be caught and handled by application using a signal
handler, so it can do some cleanup or even ignore the signal completely.
SIGKILL can not be caught and will directly kill the process without
any chance for further progressing.
And a title bar close button does normally invoke a event of the used
GUI toolkit (in case of Windows it would be the message "WM_CLOSE", I
don't know the event names of GTK and Qt :) ) and not send a SIGTERM.
The handling of the close button, menu entry etc. GUI element IMO can be
unified into a CloseQuery, possibly followed by a Close - provided that
the program/library can determine that it is the result of a GUI action,
affecting only a specific instance.
So I think this leaves two cautionary cases which arise because a term
signal can be sent to multiple programs simultaneously (e.g. by the
killall5 program). The first is that a shutdown caused by a term signal
should not attempt to e.g. save state to a .ini file if there's a risk
that that file is shared without waiting for manual confirmation. The
second is that if a shutdown presents a dialogue box this should not
have a user-friendly "I'll save your data after five seconds" default,
unless it's absolutely certain that the files won't be shared (this
might be acceptable for a WM close event, but definitely not for a signal).
Compromise: try saving all data, skipping write-locked files.
I'm not sure how to deal with unsaved data in general. A program can ask
"Sure to exit?" first, then determine whether unsaved data exist, ask
"Exit without saving?", before really terminating. But it also can
decide to exit immediately, if no data deserve saving, or to save before
asking "Sure to exit?".
Procedures even may be different for Linux and Windows, depending on the
signal/message types. Even if a program can ignore SIGTERM, can it also
inform the system that it doesn't *want* to close? On Windows a program
can stop an shutdown, maybe not on other platforms.
DoDi
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