S B

Implementing ScriptBasicMulti- Thread

How to embed ScriptBasicmulti-thread?

S B Contents

• Who this presentation is for• What is multi-thread, issues• 2 ways of mt ScriptBasic• Issues when implementing

dependent threads• Solutions for the issues

S B 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

S B 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

S B 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

S B 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)

S B 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)

S B 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

S B Dependent threads

• Threads access shared data• Example:

– session handling in web server– Long-life application „global”

variables– Locks (not flock, but memory

mutexes)

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S B 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

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S B 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

S B MT special macros and variables

#define SUPPORT_MULTITHREAD \ static MUTEX mxThreadCounter,mxInit;\ static int iFirst;\ static long lThreadCounter;

static void *pProcessLevelMemorySegment;

S B Initialization code in bootmodu

INC_THREAD_COUNTERINITLOCK 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 */

S B New control function

besSUB_KEEP long lTC;

GET_THREAD_COUNTER(lTC); if( lTC == 0 ){ INC_THREAD_COUNTER } return lTC ? 1 : 0;besEND

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S B

Thank you for your attention