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Class member synchronization

Started by murjara Mar 3, 2008 at 6:38 AM 3 replies 850+ views

Original Post

Mar 3, 2008 at 6:38 AM

hi, I have following problem: Example Class A defined as: class ClassA { private: CRITICAL_SECTION m_mutex; int var; public: ClassA() { InitializeCriticalSection(&m_mutex); var = 0; } ~ClassA() { DeleteCriticalSection(&m_mutex); } int GetVar() { EnterCriticalSection(&m_mutex); return var; LeaveCriticalSection(&m_mutex); } void SetVar(int v) { EnterCriticalSection(&m_mutex); var = v; LeaveCriticalSection(&m_mutex); } }; Methods GetVar and SetVar are being called from different threads, of cource. Problem is that my program hangs up when those methods are being called. So what I need is "class member level" synchronization. Any hints?

ToohrVyk

Mar 3, 2008 at 6:40 AM

See that "warning level" setting on your compiler? Turn it all the way up.

return var;<font color="red">LeaveCriticalSection(&m_mutex);</font>

murjara

Mar 3, 2008 at 7:40 AM

Quote:
Original post by ToohrVyk
return var;<font color="red">LeaveCriticalSection(&m_mutex);</font>

OK, problem solved, thanks, I just didn´t see that :)

SiCrane

Mar 3, 2008 at 7:46 AM

In C++ it's better practice to wrap critical section objects in a class type to ensure that all the proper matched calls are actually matched. Ex:

class Mutex {  public:    Mutex()  { InitializeCriticalSection(&cs_); }    ~Mutex() { DeleteCriticalSection(&cs_); }  private:    void lock(void)   { EnterCriticalSection(&cs_); }    void unlock(void) { LeaveCriticalSection(&cs_); }    Mutex(const Mutex &);    Mutex & operator=(const Mutex &);    CRITICAL_SECTION cs_;    friend class Lock;};class Lock {  public:    explicit Lock(Mutex & m) : m_(m) { m_.lock(); }    ~Lock() { m_.unlock(); }  private:    Lock(const Lock &);    Lock & operator=(const Lock &);    Mutex & m_;};

murjara

Mar 5, 2008 at 8:37 AM

Ok, another question:

How to determine when the thread starts waiting on event? Or how to signal event and start waiting simultaneously?

SetEvent(m_hEvent); // Set event signaled
WaitForSingleObject(m_hEvent2, INFINITE); // wait for signaling on another object.

In the code above it takes two method calls to signal and start waiting, but if
there´s multiple threads running, something may happen on other threads between those calls, so I think it isn´t exactly safe.

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