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"shellcmd" backend loses running jobs if main process is interrupted #174

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1. submit jobs to the a "subprocess" resource, e.g., with `gsub`
2. now `gstat` won't work any longer

Alternatively:

1. run jobs on the local machine using grosetta/ggamess/etc.
2. interrupt the script with Ctrl+C
3. when you resume, all jobs are considered UNKNOWN even though they must still 
be running.

What is the expected output? What do you see instead?

We assume that all backends are asynchronous and that we can always
stat/reconnect a job once it's been launched.  This is not possible
with the "subprocess" module, which uses os.wait() calls to get the
status: you can only wait() on child processes, so once you interrupt
the original process, you lose any rights on the jobs.

This is a design issue: there is no way to circumvent it unless we
launch jobs supervisioned by a "monitoring process" that uses
files/sockets to communicate with a "parent" process.  This is the
approach that Globus has taken.  

IMHO, it's not worth to pursue this further: "subprocess" usage should
be limited to debugging and not production usage.

Original issue reported on code.google.com by riccardo.murri@gmail.com on 24 Mar 2011 at 4:53

GoogleCodeExporter commented 9 years ago 
What is the alternative? We use it several places in the current code.

mike

Original comment by mrgh...@gmail.com on 24 Mar 2011 at 4:59

GoogleCodeExporter commented 9 years ago 
| What is the alternative? We use it several places in the current code.
|

This ticket refers to the new "subprocess" backend (r1332), not to the
Python module of the same name.

I guess this is an indication that the backend is badly named, since
it does not even make use of Python's subprocess :-)

Original comment by riccardo.murri@gmail.com on 24 Mar 2011 at 5:02

GoogleCodeExporter commented 9 years ago

Original comment by riccardo.murri@gmail.com on 24 Mar 2011 at 7:34

GoogleCodeExporter commented 9 years ago 
Proposal for fixing this "SubProcess" backend bug:

1. Do not execute the target executable directly, but instead use GNU
   time to wrap its execution.  GNU time can be told (via the
   `--format` option) to output also the exit code of the program it
   runs, so we just save it to a file and can reap it any time later.

   That is, if the backend gets passed an `Application` object with
   `executable='pippo'` and `arguments=['a','b','c']`, then it should
   really invoke `os.execl(['/usr/bin/time', ..., 'pippo', 'a', 'b', 'c']`
   and *not* `os.execlp(['pippo', 'a', 'b', 'c'])` as it does presently.

   Note:

   * By default `/usr/bin/time` prints its statistics to STDERR, which
     would mess up the application's own output.  So time's `--output`
     option should be used to redirect time's own output to a file.

     I suggest that the file is named `.gc3pie-stat` (or something
     similar) and located in the application execution directory.

   * ARC also uses GNU time to wrap the execution of each program; the 
     format string they use in ARC 1.1 is:

        'WallTime=%es\nKernelTime=%Ss\nUserTime=%Us\nCPUUsage=%P\nMaxResidentMemory=%MkB\nAverageResidentMemory=%tkB\nAverage
TotalMemory=%KkB\nAverageUnsharedMemory=%DkB\nAverageUnsharedStack=%pkB\nAverage
SharedMemory=%XkB\nPageSize=%ZB\nMajorPageFaults=%F\nMinorPageFaults=%R\nSwaps
=%W\nForcedSwitches=%c\nWaitSwitches=%w\nInputs=%I\nOutputs=%O\nSocketReceived=%
r\nSocketSent=%s\nSignals=%k\n'

     I suggest we use the same format (so we can write a unified
     parser) but *add* the "exit status" line.  We *need* the exit
     status saved to a file, because there's no parent process to reap
     the exit status via the `wait()` call.

   * GNU time is usually located at `/usr/bin/time`, but it would be
     nice if the `SubProcess` constructor had this as a configurable
     parameter, to be set from the `gc3pie.conf` configuration file.

     (GNU time has a few buggy versions; it would be nice to be able
     to point to a sane version on systems where the bugged one is the
     default, e.g., recent RHEL or SLES.)

2. Instead of using `os.wait()` to grab the child process status, read
   it from `/proc/PID/stat`.  When `/proc/PID/stat` exists no
   more, the process has terminated and one should go check the output
   of the `time` command above and reap the exit code and signals from it.

   There's a subtlety here: it is theoretically possible that we wait
   so much between updates that the PID of the child process has been
   re-used and we check `/proc/PID/stat` of a different process...
   It *seems* that procfs uses ever-increasing inode numbers, so we 
   should probably store the inode number of the original
   `/proc/PID/stat` file and check it -- if the inode number has
   changed, then we're no longer looking at the same
   `/proc/PID/stat`.

Original comment by riccardo.murri@gmail.com on 6 Feb 2012 at 11:45

GoogleCodeExporter commented 9 years ago

Original comment by riccardo.murri@gmail.com on 20 Jun 2012 at 6:35

GoogleCodeExporter commented 9 years ago 
Implemented in revisions 2384-2389.

We use psutil http://code.google.com/p/psutil/ to check the status of the job 
(instead of reading /proc/PID/stat file), and we use time as a wrapper for the 
application. 

A configuration option `time_cmd` for `resource` section has been added to 
specify the path to the `time` command (by default it's just `time`, which will 
point to the first binary found in PATH environment variable)

Each application's command is run through `time`, which will write its pid and 
its output in a file inside the execution dir of the application. These files 
are used by the backend to check the status of the time command and to check 
the return code of the application.

Original comment by arcimbo...@gmail.com on 21 Jun 2012 at 1:54