[fpc-devel] calls to Fpc-made library from C not thread-safe

[Michael Van Canneyt]

On Thu, 30 Nov 2006, Dominique Leducq wrote:

> Hi,
> 
> I have a library compiled with Fpc, used from C/C++ programs.
> When these C programs call functions of the library from different threads, things break.

This is unfortunately true :-)

> 
> As I understand it, the exception stack(s), the standard input/output streams, the threadID 
> and stack checking variables use thread variables, and when the thread is created from C, 
> this variables are not allocated nor initialized.

This is correct.

> As a workaround, I thought I could export a function from the library, to be called in each 
> thread before any other library call, which would call CurrentTM.AllocateThreadVars and 
> System.InitThread.

This should no longer be needed. I implemented some fixes recently which
fixes this. If you're working with an officially released version, then you
have the right solution. Calling CurrentTM.AllocateThreadVars should be
enough.


> And symetrically, a function to be called after any other library call in the thread, 
> which flushes the input/output streams and calls CurrentTM.ReleaseThreadVars.


Correct. The CurrentTM.Releasevars and flushing should be done just before your
thread ends. This should be done always, with any version of FPC.

Michael.