Hello,

While using an external C framework (Mac OS X, discrecording OS framework, FPC 2.4), I noticed that my FPC console app crashes when I use writeln's in both C threads (callbacks).

Example: Two FPC functions that are called from an external C library (c_callback1 and c_callback2) - callback2 is called within callback1 in another C thread (other than the FPC main thread).


// called from external C framework within the FPC main thread
c_callback1; cdecl;
begin
  writeln('callback1begin');
  // c_ callback2 is called here from another C thread
writeln('callback1end'); <== my FPC console app crashes here ( "EInOutError - Disk Full")
end;


// called from external C framework in another C thread
c_callback2; cdecl;
begin
  writeln('callback2begin');
  writeln('callback2end');
end;

An unhandled exception occurred at $000669E3 :
EInOutError : Disk Full
  $000669E3  CALLBACK1,  line xxx


Question: Why isn't it safe to call writeln's in non-FPC threads? Are there any other FPC runtime functions I should not call within non- FPC threads?

I'm going to make an FPC wiki page ('Threading Pitfalls') that will discuss these and other issues related to threading and I welcome all explanations on this so I can better understand this problem! :-)

Thanks,
Alexander

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