[GRASS-dev] [GRASS GIS] #2468: Python OSError: [Errno 7] Argument list too long when running grass.pipe_command repeatedly

[GRASS GIS]

#2468: Python OSError: [Errno 7] Argument list too long when running
grass.pipe_command repeatedly
---------------------------------------------------+------------------------
 Reporter:  maxnova                                |       Owner:  grass-dev@…              
     Type:  defect                                 |      Status:  new                      
 Priority:  normal                                 |   Milestone:  6.4.5                    
Component:  Python                                 |     Version:  6.4.4                    
 Keywords:  OSError, pipe_command, python, script  |    Platform:  Linux                    
      Cpu:  x86-64                                 |  
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Comment(by glynn):

 Replying to [ticket:2468 maxnova]:

 > When running grass.pipe_command many times in a row, I get:
 >
 {{{
 OSError: [Errno 7] Argument list too long
 }}}

 The error message (which comes from strerror) is misleading. From the
 documentation for
 [http://pubs.opengroup.org/onlinepubs/9699919799/functions/exec.html
 execve]:
 {{{
 [E2BIG]
     The number of bytes used by the new process image's argument list and
 environment list is greater than the system-imposed limit of {ARG_MAX}
 bytes.
 }}}

 In this case, it's the environment which is too large, not the argument
 list.

 This is caused by calling grass.script.setup.init() for each iteration.
 That function appends the GRASS-specific directories to PATH,
 LD_LIBRARY_PATH (or equivalent) and PYTHONPATH, even if they're already
 present. So those variables' values get larger with each iteration.

 This isn't a bug in grass.pipe_command (etc); you would have exactly the
 same problem if you invoked subprocess.Popen() (or os.system(), or any
 other interface for executing commands).

 The solution is not to invoke grass.script.setup.init() for each
 iteration. Instead, just create a new gisrc file with
 grass.script.setup.write_gisrc() and set os.environ['GISRC'] to the
 filename. IOW, duplicate the last two lines of grass.script.setup.init().

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/2468#comment:1>
GRASS GIS <http://grass.osgeo.org>