On Saturday, 9 March 2013 at 18:35:25 UTC, Steven Schveighoffer
wrote:
On Sat, 09 Mar 2013 11:05:14 -0500, Lars T. Kyllingstad
<pub...@kyllingen.net> wrote:
On Wednesday, 6 March 2013 at 16:45:51 UTC, Steven
Schveighoffer wrote:
On Tue, 05 Mar 2013 17:38:09 -0500, Vladimir Panteleev
<vladi...@thecybershadow.net> wrote:
I've also initially tried writing a different program:
[...]
Linux should work here. From what I can tell, you are doing
it right.
If I get some time, I'll try and debug this.
I think I know what the problem is, and it sucks bigtime. :(
Since the child process inherits the parent's open file
descriptors, both ends of a pipe will be open in the child
process. We have separated pipe creation and process
creation, so spawnProcess() knows nothing about the "other"
end of the pipe it receives, and is therefore unable to close
it.
In this particular case, the problem is that "sort" doesn't do
anything until it receives EOF on standard input, which never
happens, because even though the write end of the pipe is
closed in the parent process, it is still open in the child.
Oh crap, that is bad.
Unlike Windows which is an opt-in strategy, unix has an opt-out
strategy (there is the F_CLOEXEC flag). For consistency, I
think it would be good to close all the file descriptors before
calling exec.
I don't know how to solve this in a good way. I can think of
a few alternatives, and they all suck:
1. Make a "special" spawnProcess() function for pipe
redirection.
2. Use the "process object" approach, like Tango and Qt.
3. After fork(), in the child process, loop over the full
range of possible file descriptors and close the ones we don't
want open.
The last one would let us keep the current API (and would have
the added benefit of cleaning up unused FDs) but I have no
idea how it would impact performance.
I think 3 is the correct answer, it is consistent with Windows,
and the most logical behavior. For instance, if other threads
are open and doing other things that aren't related (like
network sockets), those too will be inherited! We should close
all file descriptors.
I think so too. In C, you have to know about these things, and
they are specified in the documentation for fork() and exec().
In D you shouldn't have to know, things should "just work" the
way you expect them to.
How do you loop over all open ones? Just curious :)
You don't. That is why I said solution (3) sucks too. :) You
have to loop over all possible non-std file descriptors, i.e.
from 3 to the maximum number of open files. (On my Ubuntu
installation, this is by default 1024, but may be as much as
4096. I don't know about other *NIXes)
Here is how to do it:
import core.sys.posix.unistd, core.sys.posix.sys.resource;
rlimit r;
getrlimit(RLIMIT_NOFILE, &r);
for (int i = 0; i < r.rlim_cur; ++i)
close(i);
Lars
