Imager::Threads(3) 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.


Tony Cook <[email protected]>