Windows XP has the limit 10000 user handles for each process and total 32000 for each desktop session. However, when I run 4 or 5 SWT process, each consuming no more than 2000 user handles, the SWT No More handles exception will always be threw.
Does anyone know why?
Answer
If I understand you correctly, you are probably getting the following exception:
org.eclipse.swt.SWTError: No more handles
You may be creating resources (such as Font, Image or GC objects) that you aren't correctly disposing. You might want to take a moment to read through the SWT guide on Managing Operating System Resources.
To determine if this is indeed the case, I can recommend this useful article: Diagnosing Handle Leaks in SWT/RCP Windows Applications, which explains what resources are and suggests using Process Explorer or DPus to locate leaks.
A colleague also highly recommends Sleak, a SWT-focused application that can actually inform you which resources are remaining in residual memory.
For a very technical understanding of what handles SWT is making, this Sybase article describes that there are three kinds: User Object, GDI Object or Kernel Object handles, each of which has its own maximum.