我的不同线程是否会看到更新的shared_ptr对象

Question

I have multiple threads reading from multiple shared objects. Each of these objects contains a shared_ptr to a Point:

struct Point
{
int x;
int y;
}

shared_ptr<Point> dataPtr=std::make_shared<Point>(Point(...init...)); // at compile time

Then I pass it to the copy constructor of my different objects

Object1 obj1 = Object1(..., dataPtr, ...)
Object2 obj2 = Object2(... , dataPtr, ...)

At some point, I will update the underlying point by doing:

dataPtr.get().x=newvalue;

I dont have to take into account any race scenario, readers will be put to sleep before writing the new value. However, I'd like to check with you that all threads will see the newvalue after the update, that this is not a "cached and dont see update" kind of scenario.

Thks

Answer 1

yes, all threads will see the new value, from cppreference:

All member functions (including copy constructor and copy assignment) can be called by multiple threads on different instances of shared_ptr without additional synchronization even if these instances are copies and share ownership of the same object.

but you don't have to use get() to access the stored pointer, this is much better style:

dataPtr->x = newvalue;