CODEWITHSUNDEEP
c++multithreadingvisual-studio-2012
Germán Diago
Germán Diago

Reputation: 7663

Cannot see std::string change in another thread visual studio 2012

I am doing something like this:

struct MyClass::Impl {
   std::string someString;

   //Invoked from thread "anotherThread"
   void callback() {
      std::cout << someString << std::endl;
   }
};


void MyClass::DoSomething() {
   //Connnect callback and fire operation in another thread
   anotherThread.Start(); 

   anotherThread.Op1();

   //Wait to finish without joining, Op1 invokes callback from another thread
   //...

   //string written in main thread
   impl->someString = someOtherString;

   anotherThread.Op2();
   //Wait to finish without joining, Op2 invokes callback from anotherThread
}

The problem is that I cannot see impl->someString change in callback, even if it has been written to. Do I need any additional synchronization? Callback only reads, but never writes that string.

Upvotes: 0

Views: 75

Answers (1)

Dietmar K&#252;hl
Dietmar K&#252;hl

Reputation: 153840

When writing a value in one thread and accessing the value in another thread you need to have appropriate synchronization. Without proper synchronization in both threads you have a data race. Any data race causes your program to have undefined behavior.

Upvotes: 3

Related Questions