[GRASS-dev] [GRASS GIS] #2153: r.viewshed fails on large raster: mktemp provides only 26 unique file names

[GRASS GIS]

#2153: r.viewshed fails on large raster: mktemp provides only 26 unique file names
--------------------------------+-------------------------------------------
 Reporter:  wenzeslaus          |       Owner:  grass-dev@…              
     Type:  defect              |      Status:  new                      
 Priority:  normal              |   Milestone:  7.0.0                    
Component:  LibRaster           |     Version:  svn-trunk                
 Keywords:  r.viewshed, mktemp  |    Platform:  MSWindows 7              
      Cpu:  Unspecified         |  
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 Citing original report from mailing list [http://lists.osgeo.org/pipermail
 /grass-dev/2013-December/066718.html r.viewshed fails on large raster:
 temp file already exists] ([http://osgeo-org.1560.x6.nabble.com/r
 -viewshed-fails-on-large-raster-temp-file-already-exists-td5095763.html
 nabble]):


 > I was running r.viewshed in GRASS 7.0 under Win7 on a large raster with
 11000 rows by 11000 columns. The algorithm ran in external memory mode
 with temporary files being written to a local directory (on C:). On
 starting sweeping, two temporary files were created, “STREAM_a06524” and
 “STREAM_b06524”, of which the first never increased in size beyond 0 KB,
 and the second grew to about 11 GB during sweeping. When sorting events,
 additional temp files were created, each of about 255 MB size, which were
 all named in the same logic, i.e. “STREAM_c06524”, “STREAM_d06524” etc,
 with only the letter after the underscore in the file name changing to the
 next letter in the alphabet. This continued until  the file
 “STREAM_z06524” had been created, then the algorithm crashed with “File
 exists” (see sh output below). Obviously it had tried to create a file
 that already existed, probably named “STREAM_a06524”. It seems that either
 the programmer never counted on more files being necessary than the
 alphabet has letters, or maybe something gets mixed up in the loop and the
 code assumes that “STREAM_a06524” does not exist because it never wrote
 any data to it.

 {{{
 ...
 ami_single_temp_name: mktemp failed: : File exists
 Assertion failed: 0, file ami_stream.cpp, line 97
 }}}

 As found by [http://lists.osgeo.org/pipermail/grass-
 dev/2013-December/066729.html MarkusN], MS Windows'
 [http://msdn.microsoft.com/en-us/library/34wc6k1f%28v=VS.80%29.aspx
 _mktemp] supports only 26 unique file names:

 {{{
 _mktemp can create a maximum of 26 unique file names for any given
 combination of base and template values. Therefore, FNZ12345 is the
 last unique file name _mktemp can create for the base and template
 values used in this example.
 }}}

 Because it [http://lists.osgeo.org/pipermail/grass-
 dev/2013-December/066729.html works] on Linux, the problem is probably
 connected only to MS Windows' `_mktemp` function.

 References:
  * http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47439 (similar report for
 gfortran)
  * http://gcc.gnu.org/ml/fortran/2011-03/msg00102/mktemp.diff (otential
 patch to be re-used)
  * http://msdn.microsoft.com/en-us/library/34wc6k1f%28v=VS.80%29.aspx
 (_mktemp at MSDN)
  * http://msdn.microsoft.com/en-us/library/t8ex5e91%28v=vs.80%29.aspx
 (`_mktemp_s` at MSDN)
  * http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3242.pdf (C++
 standard defines `tmpfile` and `tmpnam`)
  * http://www.gnu.org/software/libc/manual/html_node/Temporary-Files.html
 (GNU documentation)

-- 
Ticket URL: <http://trac.osgeo.org/grass/ticket/2153>
GRASS GIS <http://grass.osgeo.org>