multiple imagecache calls on a page for one image causes one or more img creation failures

I found that putting multiple theme('imagecache', ..)'s on a page consistently causes one or more image generations to fail, logged as a misguiding "directory is not writable" error.

example: in a cck node's .tpl.php:

print theme('imagecache', 'HistoricalMarkerImageThumb', $field_bigimage[0]['filepath']);
print theme('imagecache', 'HistoricalMarkerImageMed', $field_bigimage[0]['filepath']);
print theme('imagecache', 'HistoricalMarkerImageLarge', $field_bigimage[0]['filepath']);

Of this, typically the first call produces ..Thumb and ..Large, but not ..Med. An error is logged for ..Med. Reload of this page works fine (b/c two are already pre-gen).

I believe this is caused by multiple processes (each concurrent browser request for img-src="..." on the page) trying to access the same tmp file. It appears that an attempt at handling this was put in place in imagecache.module:~104, the test for !is_file($tmpdestination), but that completely bypasses the entire image creation routine! And since $generated = TRUE is set in both cases (if/else), the module continues along its merry way to call the missing image, adding a fistful of errors to the log.

First Recommendation:
• Make the tmp file unique:
  change :80
  $tmpdestination = file_directory_temp() . str_replace(dirname($path), '', $path);
  to
  $tmpdestination = file_directory_temp() . '/' . $preset['presetid'] . str_replace(dirname($path) . '/', '', $path);
  which would make tempfile paths like /tmp/1origimagename.jpg, /tmp/2origimagename.jpg, /tmp/3origimagename.jpg
• I opted for pathid over pathname for brevity but still unique

Second Recommendation:

• :~104-107
  

    if (!is_file($tmpdestination)) {
      $generated = TRUE;
      file_copy($source, $tmpdestination);
  

• Remove $generated = TRUE;. Add curly brace to close this conditional block. Replace "else" portion (and removed closing curly brace) of this conditional block in :130-132 with $generated = TRUE;.