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Lab3

Lab3. TA: Yi Cui 02/12/2013. Part 3. Goals Practice multiple threads programming Difficulties Synchronization Exit condition. Part 3. What does the big picture of part 3 look like? Your threads CC process Robots. Synchronization. Use critical section to protect shared data

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Lab3

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  1. Lab3 TA: Yi Cui 02/12/2013

  2. Part 3 • Goals • Practice multiple threads programming • Difficulties • Synchronization • Exit condition

  3. Part 3 • What does the big picture of part 3 look like? • Your threads • CC process • Robots

  4. Synchronization • Use critical section to protect shared data • Notification of exit • Program termination

  5. Critical section • Where do we need to use critical section? Search() { U.add (s, 0); D.add (s); while ( U.notEmpty () ) t = U.removeNextTuple () if ( t.ID == T ) break N = G.getNeighbors (t) for each y in N if ( D.find (y) == false ) U.add (y) D.add (y) }

  6. Exit condition • Find exit • No more nodes to be searched • U is empty • No active threads • What is an active thread?

  7. Notification of exit • Set a boolean flag: exit = true, false ? • Set event ?

  8. Program termination HANDLE *hSearch = new HANDLE[robot]; for (int i = 0; i < robot; i++) hSearch[i] = CreateThread(...); // wait for all threads to finish for (int i = 0; i < robot; i++) WaitForSingleObject(hSearch[i], INFINITE); DisconnectRobots(...); DisconnectCC(...);

  9. Passing parameters (C style) struct Parameters { HANDLE mutex; U D int activeThread; int totalExtracted; }; DWORD WINAPI SearchThread(LPVOID lpPara) { Parameters *p = (Parameters*)lpPara; p->U ... } Parameters para; handles[i] = CreateThread(..., SearchThread, &para, ....);

  10. Passing parameters (C++ style) class GraphSearch { public: void search(); private: HANDLE mutex; int totalExtracted; ... }; DWORD WINAPI SearchThread(LPVOID lpPara) { GraphSearch *p = (GraphSearch*)lpPara; p->search(); ... } GraphSearch gs; handles[i] = CreateThread(..., SearchThread, &gs, ....);

  11. Misc • Suppose we have 5,000 threads • Where do we create 5,000 pipes? • Where do we do 5,000 initial connection? • Initial room is always the same • Shared data • Pass by reference (do not make multiple copy of it)

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