[fpc-devel] threadvar implementation

Michael Schnell mschnell at lumino.de
Mon Aug 2 13:15:41 CEST 2010

  On 07/30/2010 08:01 PM, Hans-Peter Diettrich wrote:
> The only question is, whether you want the (absolute, flat) address of 
> the threadvar of an *specific* thread, or the address of the threadvar 
> in the *current* thread. Since the current thread can change, the 
> offset of the threadvar record will change accordingly, and must be 
> determined by the appropriate means (via segment or other address 
> register).
This is what threadvars are all about,. Of course the effective address 
needs to be different for different threads (otherwise this would be 
just static/global variables, as the virtual address mapping is defined 
to be identical for all threads of an application).

The difference between the systems I checked seems to be that the 
non-flat address (disregarding the Selector to be used) (this seems to 
be what is stored in a pointer, assuming DS: in FPC) of the threadvars 
in different threads is identical with X86/Linux and different with all 
other systems. C can handle this by defining the pointer type 
appropriately (with "__thread") while FPC does not seem to have this 


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