From the not necessarily big news, but still useful department.
The situation: for Very Good Reasons
1, you want to replace your current process by calling
exec(), but you still want to have the chance to do something after the process you exec()ed finishes.
This is a simple technique I just came up with: just before replacing the current process by calling
exec(), you
fork() a process in the background that will wait for the current process id to disappear from the process list, and then does whatever you want to do.
A simple proof-of-concept I wrote is composed of two bash programs:
wrapper and
real.
real is really simple: it just waits a few seconds and then prints its process id to the console:
#!/bin/bash
sleep 5
echo $BASHPID
wrapper is the program that handles the situation we want to exercise: it replaces itself with
real, but still has the chance to do something after
real finishes. In this case,
wrapper notifies the user that
real finished.
#!/bin/bash
echo $BASHPID
real_program_pid=$BASHPID
(
while ps -p "$real_program_pid" >/dev/null; do
sleep 0.1s
done
notify-send 'real program finished'
) &
exec ./real
One nice property that
wrapper explores is that when
exec() starts
real, it really replaces
wrapper, and therefore has the same process id (in this case accessible by bash in the
$BASHPID variable). Because of this, the background process that
wrapper starts just before the
exec() call already knows which process it has to watch for.
The actual code for waiting is not optimal, though. I cannot use
waitpid() (the
wait builtin in bash), since
real is not a child process of
wrapper. I went with a brute force approach here, and I am pretty sure there is a cheaper way to wait for a random
PID without a busy loop (but that wasn t the point here).
1
update: I
am aware of the classic
fork()/
exec() pattern. My Very Good Reasons include the fact that I can t control the flow: I am writing a plugin for a program that calls its plugins in sequence, and after that, calls
exec(), but my plugin is interested in doing some work after
exec() finishes.
I've just finished reading Graham Joyce's haunting The Silent
Land:
an atmospheric and moving love story set in an Alpine ski resort.
Husband and Wife Jake and Zoe head out to the slopes early one morning
and are caught in an avalanche. They survive, narrowly, but upon
returning to the resort, everything has changed
Anyone who has read any quantity of SF or fantasy will probably make
an early guess at what's going on, and you'd most likely get it wrong.
Even if you know where you're going, the journey is often the point,
rather than the destination, and this journey is pretty gripping.
I do most of my reading on the train to and from work. I often listen
to music when I'm reading and I try to choose things which aren't going
to distract my attention from the book too much. Film soundtracks are
good; so is classical; so is a lot of Eno's work.
For this book I mostly listened to the score from the latest film
version of The Girl with the Dragon
Tattoo, by Trent Reznor and Atticus Ross.
Clocking in at only seven minutes shy of three hours, this is a haunting
score that evokes a cold, isolated Swedish winter, and thematically
matched the book perfectly. The score is a little less accessible than
their previous work, but is rewarding on repeat listen. You can get a
free 6-track sampler at the website linked above.
![[pic]](http://jmtd.net/log/./expedit/image1.jpg)
I have a laptop used for playing music (and occasionally also videos) which is currently running Windows XP with XBMC. Reinstalling this beast to Linux is on my todo list for ages and now I've finally found time to try that.
Starting 
I had a bit of an adventure yesterday, which would have taken some
explaining if the police had gotten involved. It went a little something
like this...
My friend and former co-worker Sara was in the US Virgin Islands for the
holidays. Her boyfriend, Karl, flew there separately for the tail end of her
time there.
Yesterday, I received a phone call from Sara, saying that Karl had managed
to fly out to the Virgin Islands without his passport. Apparently you can
get there without one, but to get back into the mainland US, you need one.
She wanted to know if I could get one of my lock-picking co-workers to break
into their apartment and retrieve Karl's passport and mail it them. Karl was
supposed to fly out the next day. Attempts by Sara to contact her landlord
had failed, so they didn't have many other options (apart from mailing me a
key, which would have cost them another day).
I asked one of my co-workers, Jason, who I knew was into lock picking, if he
was up for it, and he offered to put me in touch with another guy who had
dominated the recent lock picking night that he'd run.
So now I'm talking to David, who's on board with the mission, but doesn't
have his lock picking gear on him. No problem, Jason says he'll lend me his,
which was at work with him. So we have a plan.
Our friends Ian and Melinda are currently in Australia. They've lent us
their car because it's leased, and they have some minimum mileage they're
supposed to do and they're under it, so I've been driving to work in their
car some days. As it happens, I drove to work in it yesterday.
So now David and I set out in a car that neither of us own, with a lock
picking set that belongs to another person, to break into an apartment of
someone who's in the Virgin Islands. What could possibly go wrong?
I'm told that it's not illegal to own a lock picking set, but if you're
caught with one on your person and you're not a locksmith, you can get into
all sorts of trouble. On top of that I'd have a hard time explaining the car
I'm driving.
We get to Sara and Karl's condo complex. It has a common gate that visitors
would normal get buzzed through. Turns out it's not that hard to climb over.
It's got some benign-looking spiky things on top, but I could get a leg
over from the left hand side of the gate and jump over without impaling
myself. Then I let David in and we proceeded upstairs to Sara and Karl's
apartment door, where David set to work.
Sara said that just the dead bolt was locked. David started at it with
Jason's tools, trying to be as discreet as possible. It was about 3:30pm and
there was no one around, but we could hear some noises from the neighbouring
apartment (the two front doors were right next to each other).
After what felt like about half an hour without success (the last pin of the
lock was particularly tricky apparently) David was having to resort to more
noisy techniques with the lock, so I decided to take the up-front approach
and just inform the next door neighbour what we were doing in case he/she (I
think it was a she) decided to call the cops on us. I told her through the
door why we were there and what we were doing. She didn't seem to care too
much.
David then proceeded to start "raking" the lock, essentially brute forcing
the pins with a lot of jiggling, and finally managed to pick it and we were
in. I quickly found Karl's passport where it was suspected to be, and then
we pondered how we were going to lock the door again.
We could have just locked the door knob instead of the deadbolt and closed
the door behind us, but we weren't sure if Sara and Karl had a key to the
doorknob (Sara said they always just locked the deadbolt). Sara was fine
with leaving the door unlocked until they got home, but weren't so keen on
leaving our fingerprints all over the place and then leaving the door
unlocked.
David tried to re-pick the deadbolt so that he could lock it via the same
means as opened it, and I scouted around for a key. I managed to find a key
that locked both the deadbolt and the doorknob, so I took that with us and
locked up their apartment. In David's defense, the deadbolt was a bit stiff
to lock even with the key.
I dropped David back at work, collected my stuff (it was now about 4:30pm)
and headed to the UPS Store to ship Karl's passport to him as fast as
humanly possible. I just made the 5pm pick up.
Today I received an SMS from Sara informing me that they had received the
passport. I was very impressed with how fast it got to them.
So that was all a bit of an adventure. I'm not sure how much longer Karl is
going to have to stay in the Virgin Islands as a result. I'm going to
suggest that Sara and Karl leave a spare key with someone in future.
After dist-upgrading my main 
Since I am currently working on a Windows machine at work I am looking for ways to make this thing work in a sane way. The latest insane thing is the fact that I wasn't able to log on a CVS server at work from WinCVS (which uses CVSNT) with my regular credentials, while the cached password in Cygwin did work with the Cygwin CVS.
Current status
Back in September,
I 
new year, old hobby: trying to fix an RC bug per day, & reporting about
it. here's the first episode of 2012:
