Detailed explanation of C++ function parameters: asynchronous mechanism of parameter passing in coroutines

The parameter passing in the coroutine adopts an asynchronous mechanism. The parameter value will not be copied before execution, but obtained dynamically. This mechanism provides flexibility, allowing the coroutine to adjust parameters at runtime or pass parameters lazily. The specific steps are as follows: Traditional function parameter transfer: synchronous transfer, the actual parameters are copied to local variables before the function is executed. Coroutine parameter passing: asynchronous transfer, the coroutine uses the coroutine pointer to obtain the actual parameter value during execution.

C Detailed explanation of function parameters: asynchronous mechanism of parameter passing in coroutines

Coroutines are lightweight threads that allow programs to execute concurrently Multiple tasks without creating multiple operating system threads. The parameter passing mechanism of coroutines is different from that of traditional functions. It adopts an asynchronous mechanism.

Traditional function parameter passing

In a traditional function, parameter passing is synchronous, which means that all parameter values ​​are copied to local variables before the function is executed. For example, consider the following function:

void foo(int a, int b) {
  // ...
}

When this function is called, the values ​​of the actual parameters a and b are copied to the function's local variables a and b.

Coroutine parameter passing (asynchronous)

In a coroutine, parameter passing is asynchronous, which means that the coroutine does not copy the parameter value before execution. Instead, it dynamically obtains parameter values ​​during coroutine execution.

Consider the following coroutine version of the previous function:

coroutine foo(int a, int b) {
  // ...
}

When this coroutine is called, the values ​​of the actual parameters a and b are not copied to the local variables of the coroutine. Instead, the coroutine will use the coroutine pointer to obtain the actual parameter value during execution.

Practical Exercise

The following code shows how to use the coroutine parameter passing mechanism:

#include <coroutine>

struct Task {
  int a;
  int b;
};

coroutine process(Task task) {
  // 使用 await 暂停协程，等待外部提供参数
  auto [a, b] = co_await task;

  // 执行任务
  // ...
}

int main() {
  // 创建一个 Task 对象
  Task task{42, 23};

  // 启动协程，并提供参数
  process(task);

  return 0;
}

In this example, process coroutine from Task Asynchronously obtains parameter values ​​from the object. Since the execution of the coroutine is pauseable, it can wait for parameter values ​​to be provided externally.

Conclusion

The asynchronous parameter passing mechanism in coroutines provides flexibility for concurrent programming because it allows coroutines to dynamically obtain parameter values. This is useful in situations where you need to adjust parameters at runtime or delay parameter passing.

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