On 31May2015 23:33, Cecil Westerhof <ce...@decebal.nl> wrote:
At the moment I have the following code:
os.chdir(directory)
for document in documents:
subprocess.Popen(['evince', document])
With this I can open several documents at once. But there is no way to
know when those documents are going to be closed. This could/will lead
to zombie processes. (I run it on Linux.) What is the best solution to
circumvent this?
The standard trick is to make the process a grandchild instead of a child.
Fork, kick off subprocess, exit (the forked child).
But provided you will collect the children eventually then zombies are only
untidy, not very resource wasteful. They are essentially just slots in the
process table left around so that exit status can be collected; the resources
associated with the full process (memory, open file, etc) have already been
freed.
I was thinking about putting all Popen instances in a list. And then
every five minutes walk through the list and check with poll if the
process has terminated. If it has it can be released from the list.
Of-course I need to synchronise those events. Is that a good way to do
it?
It is reasonable.
Alternatively, and more responsively, you could have a process collection
Thread. It would loop indefinitely, calling os.wait(). That will block until a
child process exits (any of them), so it is not a busy loop. When wait()
returns, look up the pid in your list of dispatched subprocess children and do
whatever cleanup you intend. (If it is just zombies, the os.wait() cleans that
part for you.)
One thing you do need to keep in mind with such a task is that it will
os.wait() _all_ child processes. If there are other children which exit, not
spawned by your specific calls (earlier children or children made by some
library function), you must be prepared to receive pids which (a) are not in
your list of "evince" etc tasks and (b) to be collecting pids which other
subsystems might have wanted to collect themselves. The latter is uncommon (at
least, uncommon for such things to occur and you the programmer to be unaware
of them).
Anyway, that is simple and effective and immediate.
Cheers,
Cameron Simpson <c...@zip.com.au>
If everyone is thinking alike, then someone isn't thinking. - Patton
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