What “thread safe” really means…In Practical terms

Question

please bear with my newbie questions..

I was trying to convert PDF to PNG using ghostscript, with ASP.NET and C#. However, I also read that ghostscript is not thread saf

Answer 1

I am a Ghostscript developer, and won't repeat the general theory about thread safety.
We have been working on getting GS to be thread safe so that multiple 'instances' can be created using gsapi_new_instance from within a single process, but we have not yet completed this to our satisfaction (which includes our QA testing of this).
The graphics library is, however, thread safe and the multi-threaded rendering relies on this to allow us to spawn multiple threads to render bands from a display list in parallel. The multi-threaded rendering has been subjected to a lot of QA testing and is used by many commercial licensees to improve performance on multi-core CPU's.

You can bet we will announce when we finally support multiple instances of GS. Most people that want to use current GS from applications that need multiple instances spawn separate processes for each instance so that GS doesn't need to be thread safe. The GS can run a job as determined by the argument list options or I/O can be piped to/from the process to provide data and collect output.