Implement rlimit() on BSD

[NicolasLM]

In most cases a process running out of file descriptors is a sign that the software does not behave correctly. Psutil currently gives the number of fds opened by a process, but not how many can it open.

On Linux this information is available through /proc/<pid>/limits.

This metric per process would be complementary of system wide limits described in #720.

[giampaolo]

Actually that info is already retrievable via stdlib resource module:

>>> import resource
>>> resource.getrlimit(resource.RLIMIT_NOFILE)
(1024, 4096)

Doing the same via /proc/pid/limits would add the ability to do the same for all processes (instead of just os.getpid()) in case the default value gets modified by a specific process, but I'm not sure how much that's valuable considering it would be linux only.

[NicolasLM]

I ended implementing something like NicolasLM/sauna@f9a7a52#diff-4cdd796dc1ec5ac72502aab351c123a2R86

It would be surprising if other OSes than Linux do not provide a way to fetch this information as well.

[giampaolo]

Most (all?) UNIX systems provide a way to know the number of default maximum fds each process can open and #720 is meant to expose that information. /proc/<pid>/limits differs in that it provides the information for any specific process and also returns the updated information in case the user changes the default limits and AFAIK that is only possible on Linux. Other UNIX flavors are able to do the same (provide updated info) only for the current process (via resource module). As such the change you are proposing would be Linux-only.

[NicolasLM]

I'm pretty sure other platforms provide this information as well, for instance on freebsd procstat -l <pid> gives the rlimits of the process of your choice.

[giampaolo]

What other platforms are you talking about? Are you sure it's updated info and not the default system setting info being reported insted?

[NicolasLM]

I just tried on freebsd, indeed it is possible to fetch the actual limits of a process:

$ procstat -l 841
  PID COMM             RLIMIT                  SOFT             HARD      
  841 python2.7        openfiles              14049            14049

>>> import resource 
>>> resource.setrlimit(resource.RLIMIT_NOFILE, (512, 1024))

$ procstat -l 841
  PID COMM             RLIMIT                  SOFT             HARD         
  841 python2.7        openfiles                512             1024     

[giampaolo]

Getting back to this. Actually I totally forgot it is already possible to do this on Linux:
https://pythonhosted.org/psutil/#psutil.Process.rlimit
Doing the same on FreeBSD would certainly be welcome though. I will try to strace procstat command and try to see what it relies on internally. Linux relies on "man 2 prlimit":
http://linux.die.net/man/2/prlimit
...and that looks like it's Linux only, hence why I am not sure how FreeBSD (or any other UNIX variant) provides this.

[giampaolo]

@glebius just in case you want to give it a try. ;-)