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Re: Bash doesn't launch the applications directly.




"Eric Blake" <ebb9@byu.net> ååææ 496F34BB.6080200@byu.net">news:496F34BB.6080200@byu.net...
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According to Lenik on 1/14/2009 5:59 PM:
Hi, all

I noticed that when bash launches a program, for example win32
notepad.exe or cygwin sleep, it in fact launches another bash which
launches the final program,

Any idea?

Yes. It's called forking (a concept that Windows does not have natively, but which cygwin does a LOT of work to emulate). The way Unix apps (including bash) start another program is to first fork themselves, then in that fork, exec the target program. The fork accounts for the second bash process.

Depending on the nature of the called process, you might also see those
additional processes stick around.  If the child is a cygwin process (like
sleep), exec() is decently emulated, where the forked bash goes away and
you are left with only one running sleep process.  But if it is a windows
How fast does the emulation implemented?

process (like notepad), cygwin has to insert a shim process in between to
handle signal handling in order to abort notepad if you type ctrl-c in
bash, as well as collect the correct exit status.
Is there any option to disable the shim process?

I have tried to launch notepad in background:
# calc &
In such situation, we won't ever press ctrl-c or ctrl-z, (maybe until fg %1), but there still got 2 bash processes. If I just want to send the launch signal to win32, and don't care what if user press ctrl-c in the bash.


I tried `cygstart `which notepad`', this did launch another bash, too (while it launches cygstart.exe and which.exe additionally). Though the cygstart and shim are then immediately terminated, but it cost the launching time.


Ultimately, bash could be made faster by using posix_spawn() instead of fork(), for much of what it does. However, that would require 1) an upstream patch to bash to use posix_spawn(), including a fallback implementation of posix_spawn on platforms that don't yet implement it (such an implementation is possible, since gnulib already provides one, but the upstream maintainer is hard to convince, and even if the patch existed, it has already missed the bash 4.0 cutoff), and 2) an implementation of posix_spawn() in cygwin that directly spawns processes using native Windows concepts (the bash fallback implementation of posix_spawn() would still end up using fork() under the hood, giving no speedups until we have a native version). http://cygwin.com/acronyms/#PTC

Is it possible to make cygstart as a bash built-in? And thus will get another benefit that after cygstart.exe terminated, the parent-children relationship between the bash and notepad can be maintained.

Lenik



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