Implementing ScriptBasic Multi- Thread

1. Implementing ScriptBasicMulti- Thread How to embed ScriptBasic multi-thread?

2. Who this presentation is for What is multi-thread, issues 2 ways of mt ScriptBasic Issues when implementing dependent threads Solutions for the issues Contents

3. Who this presentation is for • Curious (why things happen?) • Want to learn and understand how ScriptBasic works • Want to embed ScriptBasic into multi threaded application NOT for those, who just • want to program in scriba

4. What is multi-thread? • A single process runs several threads simultaneous • A thread has its own stack and call sequence • Threads share memory and other process resources • UNIX thread is just a process w/o separate data

5. Issues regarding threads • Don’t use global variables (except for constant values, like ScriptBasic syntax definition tables) • Carefully design locking mechanisms • Free memory yourself, don’t rely on OS

6. Enabling MT ScriptBasic • No global variables • No memory leaking • Object oriented approach (although it is C and not C++) • Thread and lock primitives for portability (thread.c)

7. Two way of MT embedding • Independent threads (ex: Eszter SB Engine v1.0b22) • Dependent threads, long-life worker threads(ex: Eszter SB Engine v1.0b23)

8. Independent threads • Threads run independent of each other • Possibility and advised to share configuration file • Possibility and advised to cache program code in memory (though even v1.0b22 does not) • Can’t and should not share support function table

9. Dependent threads • Threads access shared data • Example: • session handling in web server • Long-life application „global” variables • Locks (not flock, but memory mutexes)

10. Thread life-time and ST object life time ST ST ST Basic thread ST ST ST Basic thread Basic thread ST Basic thread ST Basic thread PROCESS Pseudo Interpreter (config, global ST) Module worker thread Basic thread Basic thread

11. Initializing and using global ST • InitModuleInterface • Initializes the module Support Function Table • InheritModuleInterface • Sets the Support Function Inherit pointer but has NO effect on the object Support Function Table

12. Module life-time Moduleinstance counter 1 Basic thread 2 Basic thread 1 PROCESS PROCESS 0 Module worker thread 1 2 Basic thread 3 Basic thread Basic thread 2 1

13. Worker thread initialization • DllMain (W32) or _init (UNIX) has no ST • bootmodu is called for each thread • Solution: use bootmodu with the help of • basext.h macros • Process level global variables

14. MT special macros and variables #define SUPPORT_MULTITHREAD \ static MUTEX mxThreadCounter,mxInit;\ static int iFirst;\ static long lThreadCounter; static void *pProcessLevelMemorySegment;

15. Initialization code in bootmodu INC_THREAD_COUNTER INITLOCK if( iFirst ){ /* inherit malloc and free from pMemorySegment */ pProcessLevelMemorySegment = besINIT_SEGMENT(pSt->pEo->pMemorySegment,NULL); besCreateThread(&hT,worker_thread, pSt->pEo->pSTI); iFirst = 0 } INITUNLO /* unlock the init mutex */

16. New control function besSUB_KEEP long lTC; GET_THREAD_COUNTER(lTC); if( lTC == 0 ){ INC_THREAD_COUNTER } return lTC ? 1 : 0; besEND

17. Module life-time using besSUB_KEEP Moduleinstance counter 1 Basic thread 2 Basic thread 1 PROCESS PROCESS 1 Module worker thread 1 2 Basic thread 3 Basic thread Basic thread 2 1

18. Thank you for your attention