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Multi-threaded programming with NSPR

Multi-threaded programming with NSPR. Larry Hardiman. Overview. What is NSPR? Why program using threads? What you need to program with threads NSPR’s thread abstraction Thread synchronization using locks Thread synch using condition variables Techniques for high performance threads.

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Multi-threaded programming with NSPR

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  1. Multi-threaded programming with NSPR Larry Hardiman

  2. Overview • What is NSPR? • Why program using threads? • What you need to program with threads • NSPR’s thread abstraction • Thread synchronization using locks • Thread synch using condition variables • Techniques for high performance threads

  3. What is NSPR? • Original NSPR 1.0 was NS Java base • NSPR 2.0 began in early 1996 • NSPR 2 is platform abstraction • No GUI • Threading, thread sync • File and Socket I/O • Time, IPC, ...

  4. Why program using threads? • Simplify program design • Improve performance when calling blocking functions • Utilize all processors on multi-processor systems

  5. Thread Programming Basics • Thread Management • Thread private data • Thread synchronization

  6. Thread Management • PR_CreateThread() • PR_Interrupt() • PR_JoinThread() • PR_SetThreadPriority() • PR_GetThreadPriority()

  7. Creating a thread 1 #include “prthread.h” 2 PRThread * 3 PR_CreateThread( 4 PRThreadType type, /* user or system */ 5 (void)(start)(void *arg), /* function */ 6 void *arg; /*argument to start function */ 7 PRThreadPriority priority, /* low, norm … */ 8 PRThreadScope scope, /* local, global */ 9 PRThreadState state, /* joinable? */ 10 PRInt32 stacksize );

  8. Thread Private Data Think of “thread private data” as global variables, but for exclusive use for a single thread. Void (*PR_ThreadPrivateDTOR)(void*); PRStatus PR_NewThreadPrivateIndex( int *ndx, (dtor)); PRStatus PR_SetThreadPrivate( ndx, *priv ); void* PR_GetThreadPrivate( ndx ); See: mozilla/nsprpub/pr/tests/tpd.c

  9. Thread sync using PRLock 1 #include “prlock.h” 2 PRLock *lock; 3 lock = PR_NewLock(); 4 PR_Lock(lock); 5 /* operate on your data … */ 6 PR_Unlock(lock); 7 PR_DestroyLock(lock);

  10. Using Condition Variables 1 PRIntn data = 0; /* Thread A */ 2 PRLock *lock = PR_NewLock(); 3 PRCondVar *cvar = PR_NewCondVar(lock); 4 PR_Lock(lock); 5 while( data == 0 ) 6 PR_WaitCondVar( cvar, timeout ); /* lock released while blocked. */ /* re-locked at fall through */ 7 data = 0; /* satisfy Thread B’s condition */ 8 PR_NotifyCondVar( cvar ); 9 PR_Unlock( lock );

  11. Using Condition Variables /* Thread B */ 4 PR_Lock(lock); 5 while( data == 1 ) 6 PR_WaitCondVar( cvar, timeout ); /* lock released while blocked. */ /* re-locked at fall through */ 7 data = 1; 8 PR_NotifyCondVar( cvar ); 9 PR_Unlock( lock );

  12. What Not to Do 1 PRLock *lock; 2 PRCondVar *cv; 3 PR_Lock( lock ); 4 PR_WaitCondVar( cv, PR_INTERVAL_NO_TIMEOUT ); /* implies state in *cv */ 5 /* do something */ 6 PR_Unlock( lock ); There is no state in a PRCondVar.

  13. … More What Not to Do 1 PRBool dataIsAvailable = PR_FALSE; 2 PR_Lock( lock ); 3 if ( !dataIsAvailable ) 4 PR_WaitCondVar( cv, PR_INTERVAL_NO_TIMEOUT );/* Bad! dataIsAvailable may change during wait */ 5 /* work on the available data */ 6 PR_Unlock( lock ); The lock is released during PR_WaitCondvar(). Other threads can change dataIsAvailable. Use the while() loop;test, wait, test again.

  14. Condvar Example A hacked cvar.c goes here.

  15. High Performance Threads • … you are protecting data, not code • partition assets so that you protect the smallest piece possible • hold exclusive control as short a time as possible

  16. Bibliography • David R. Butenhof, "Programming with POSIX Threads", Addison-Wesley, 1997 • Steve Kleiman, et.al, “Programming with Threads”, Prentice Hall, 1996 • NSPR group, “NSPR Reference”, Ch. 1, 3, 5, 6. http://www.mozilla.org/projects/nspr/reference/html/index.html • UseNet newsgroup: comp.programming.threads.

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