qt multi threads

[weixj2003ld]

Thank you for answering my question patiently.
My program built with qt4.3.1,and a lot of things have been done by other people,I am afraid I can not change it to upper version.but Q4.3.1 does not support Qt Concurrent.
I think I will manage the threads by myself ,but not Qt Concurrent.
My questions:
1.What should I do if I want to let Q4.3.1 support Qt Concurrent?
2. Can data type( class defined by user) be shared by threads?
Thank you.

[wysota]

Thank you for answering my question patiently.
My program built with qt4.3.1,and a lot of things have been done by other people,I am afraid I can not change it to upper version.but Q4.3.1 does not support Qt Concurrent.

Why can't you upgrade Qt?

2. Can data type( class defined by user) be shared by threads?

Not without proper synchronization. If you do synchronize using a mutex, then it can be shared. Some of the classes will be safe without synchronization but it depends on a case by case basis. And in general widgets can't be shared between threads, regardless if you do the synchronization or not.

[weixj2003ld]

A class(defined by myself) shared by the threads must be lock and unlock?

[talk2amulya]

yes, using mutex

[weixj2003ld]

when I used two threads like what I have said in my program and compile and run it,it will be crashed at radom position,Is it because of my not synchronizing my threads?Must I synchronize them?

[talk2amulya]

if there is a shared object, u have to make it thread-safe..and yes, synchronize..and again, why cant u upgrade Qt? u have a solution waiting for u in there, so i cant understand ur reluctance

[weixj2003ld]

Thanks for answer.
1.Why have not upgrate my Qt?
My colleagues and I all use qt4.3.1+ mysql+coin3d+msvc2005+carnac.If I upgrate my qt,they must.And a lot time will be wasted for built platform again.
2.If threads only read(not write) data from the shared class(created by myself),Must it be locked and unlocked?like this:
.....

class Mythread1
{
     public:
      Mythread1(SharedClass *sharedclass);
     void calculate(SharedClass *sharedclass)
     {
           //read data from sharedclass and calculate
      }
}
 
 
SharedClass *sharedClass=new SharedClass ();
init(A);
thread1=new Mythread1(A);
thread2=new Mythread1(A)
.....

class Mythread1
{
     public:
      Mythread1(SharedClass *sharedclass);
     void calculate(SharedClass *sharedclass)
     {
           //read data from sharedclass and calculate
      }
}


SharedClass *sharedClass=new SharedClass ();
init(A);
thread1=new Mythread1(A);
thread2=new Mythread1(A)
.....

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Do I use mutex in SharedClass ?That is,must all the functions and varables in SharedClass be locked and unlocked?for example ,SharedClass like this:

class SharedClass 
{
   public:
      A *a;
      B *b;
     QString str;
    void function1();
}

class SharedClass 
{
   public:
      A *a;
      B *b;
     QString str;
    void function1();
}

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How could I do?
Thank you.

[talk2amulya]

read about thread-safe classes.. thread-safe classes are those classes for which multiple threads can access the SAME instance of the class..u have to provide synchronization in these classes..i dunno what your application is doing..u have a number of possibilities to implement synchronisation depending upon what ur class does..

and you should consult with your fellow colleagues about the new Qt version...there r lots of other features that u will be missing and implementing yourself..which is MORE wasted time

[weixj2003ld]

class SharedClass will be shared by all threads,and it structure is like this:

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
           a=new A();
           b=new B();
 
      }
}

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
           a=new A();
           b=new B();
           
      }
}

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If I will let it thread-safe,Do I do like this?

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
         QMutexLocker locker(&mutex);
           a=new A();
           b=new B();
 
      }
   private:
      mutable QMutex mutex;
}

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
         QMutexLocker locker(&mutex);
           a=new A();
           b=new B();
           
      }
   private:
      mutable QMutex mutex;
}

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class a and b must be thread-safe also?

[weixj2003ld]

no answer ??

[wysota]

no answer ??

We have no idea what you are asking for. At least I know I don't...

[weixj2003ld]

We have no idea what you are asking for. At least I know I don't...

Sorry.
I explain my question again.
As we know ,if a class is shared by muti-threads,it should be thread-safe.Now I define a class ,and it will be shared by 2 threads.If I want to let it thread-safe,I do as follow,Am I right or not?

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
           a=new A();
           b=new B();
 
      }
}

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
           a=new A();
           b=new B();
           
      }
}

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If I will let it thread-safe,I add code like this:

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
        QMutexLocker locker(&mutex);
           a=new A();
           b=new B();
 
      }
   private:
      mutable QMutex mutex;
}

class SharedClass 
{
     public:
      A *a;
      B *b;
      QString str;
      void function1()
      {  
        QMutexLocker locker(&mutex);
           a=new A();
           b=new B();
           
      }
   private:
      mutable QMutex mutex;
}

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By the way,Must class a and b be thread-safe?

[wysota]

If you post a code snippet without appropriate tags one more time, you will get a temporary ban on the forum.

No, a and b don't have to be thread safe.