The relationship between C++ function parameter passing methods and thread safety

Function parameter passing method and thread safety: Value passing: Create a copy of the parameter without affecting the original value, usually thread safe. Pass by reference: Passing the address, allowing modification of the original value, usually not thread-safe. Pointer passing: Passing a pointer to an address is similar to passing by reference and is usually not thread-safe. In multi-threaded programs, reference and pointer passing should be used with caution, and measures should be taken to prevent data races.

C The relationship between function parameter passing method and thread safety

In C, function parameters can be passed by value or reference or passed by pointer. Different transfer methods will affect the relationship between the parameter value and the original value of the function, and also affect the thread safety of the function.

Passing by value

Passing by value creates a copy of the parameter. This means that any modification to the parameter value inside the function will not affect the original value. Therefore, passing by value is generally thread-safe because functions cannot modify the original value of the passed object.

void increment(int x) {
  ++x;
}

int main() {
  int y = 10;
  increment(y);
  cout << y << endl; // 输出 10
}

Pass by reference

Pass by reference will pass the address of the parameter. This means that modifications to the parameter value within the function will also modify the original value. Therefore, passing by reference is generally not thread-safe because a data race can occur if multiple threads modify the same reference at the same time.

void increment(int &x) {
  ++x;
}

int main() {
  int y = 10;
  increment(y);
  cout << y << endl; // 输出 11
}

Pointer passing

Pointer passing will pass a pointer to the parameter address. This means that the original value can be modified via the pointer inside the function. Like passing by reference, passing by pointer is generally not thread-safe because a data race can occur if multiple threads modify the original value through the pointer at the same time.

void increment(int *x) {
  ++*x;
}

int main() {
  int y = 10;
  increment(&y);
  cout << y << endl; // 输出 11
}

Practical case

In a multi-threaded program, suppose we have a global variable counter, which is used to record the number of events that occur. To safely increment counter from a different thread, we can use the following function:

void incrementCounter(int &counter);

By using pass by reference, the function can access the actual value of counter and manipulate it Revise. Because the reference is thread-safe, this function can be safely called from multiple threads to update the counter without creating a data race.

Conclusion

Choosing the correct way to pass function parameters in C is crucial to ensuring thread safety. Passing by value is generally thread-safe, while passing by reference and pointer are generally not thread-safe because they allow the original value to be modified. In multithreaded programs, reference passing and pointer passing should be used with caution, and measures should be taken to prevent data races.

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