fpc_AnsiStr_Assign might have issues with thread safety.

Original Reporter info from Mantis: runewalsh

• Reporter name:

Description:

If this bug is a thing at all, it will happen under very tight timing conditions, so probably no one will be able to reproduce it. But please listen.

Among other things, fpc_AnsiStr_Assign(var destS: pointer; S2: pointer) does the following (in that order):

fpc_ansistr_decr_ref (DestS);
DestS := S2;

So AFTER the reference count was decremented but BEFORE S2 value assigned, another thread will see a dangling pointer.
Here's the supposed fix:

var old: pointer;
old := InterlockedExchange(DestS, S2);
fpc_ansistr_decr_ref(old);

Or, instead of fpc_ansistr_decr_ref, it will be better to have its specialized version that won't treat 'old' as var-parameter, so no writing it to stack, reading back, and writing 'nil' again.

Mantis conversion info:

• Mantis ID: 39017
• Build: trunk@49516
• Fixed in version: 3.3.1