Imager::Threads - Imager and threads


  use Imager;
  use threads;



Starting from version 0.94 Imager attempts to work safely with perl's ithreads.

Previous versions stored some state in global variables, in particular the internal error stack.

However there are some limitations:

  • Imager's debug malloc isn't thread safe and will never be. Imager's debug malloc is disabled by default.

  • libtiff, which Imager uses for TIFF file support is not thread safe, Imager::File::TIFF works around this by single-threading its access to libtiff.

  • giflib, which Imager uses for GIF support is not thread safe before version 5. Imager::File::GIF works around this by single threading its access to giflib.

  • T1Lib, used by one of Imager's font drivers, is not thread safe. Imager::Font::T1 works around this by single threading access.

  • killing a thread reading or writing TIFF or GIF files, or using T1 fonts through Imager::Font::T1 may deadlock other threads when they attempt to read or write TIFF or GIF files, or work with Type 1 fonts.

  • Fill, font, color or I/O layer objects created in one thread are not valid for use in child threads. If you manage to duplicate such an object in another thread, you get to keep both pieces when it breaks.

Note that if you have another module using libtiff, giflib or t1lib it may interact with Imager's use of those libraries in a threaded environment, since there's no way to co-ordinate access to the global information libtiff, giflib and t1lib maintain.

Imager currently doesn't use threads itself, except for testing its threads support.


Imager, threads


Tony Cook <>