RE: multithreading

[Joseph Benden]

I am pretty sure the GNU Prolog is not thread-safe in how you are calling it.  This is what I am doing with success:

 

On Linux:  I am using multiple process (a preforking) server, and after the accept and fork, then call Start_Prolog.

 

On Windows: I have the GNU Prolog wrapped into a DLL.  On the DLL_PROCESS_ATATCH I call Start_Prolog. Then each thread waits on a master critical section before calling any prolog routines (inside the dll, on each call).

 

I do not believe GNU Prolog is thread-safe because it uses global memory space for its' stacks.  If you only ever read the memory, you should be safe, but writing is a different story.  One could put mutex locks in the term reading and writing functions.  But that would be a big project, and would slow the prolog down.  GNU Prolog would have to use thread-local stacks, but that would require a re-write of the entire prolog, and would make multiple thread unable to access other threads stacks.

 

To get the same performance under windows as linux, load multiple instances of the DLL and marshal into them.

 

Joseph Benden

Systems Development/Network Administrator

AdWriter, Inc.

 

Professional member of the Association for Computing Machinery, Inc.

Professional member of the Network and Systems Professionals Association, Inc.

 

-----Original Message-----
From: address@hidden [mailto:address@hiddenOn Behalf Of Mihir Malviya
Sent: Saturday, December 01, 2001 6:40 AM
To: address@hidden
Subject: multithreading

Hi,

    Is the gprolog interface thread-safe? I seem to be having problems trying to use it with the pthread library on Linux. I'm using gprolog-1.2.1 on a Linux box. The particular problem that I face is that if I call Start_Prolog() in one thread and the other calls in a second thread , the program gives a segmentation violation.

The second problem that I face is that if I call Start_Prolog() , Stop_Prolog() in a loop , the program dumps after 128 cycles...... , the problem aggravates in later releases with the present gprolog-1.2.8 running only for 28 cycles.   Is there a memory leak ?

Regards,

Mihir.