How do I implement reentrancy in C?

How do I implement reentrancy in C?

Reentrancy in C means that a function can be interrupted and safely called again ('re-entered') before its previous executions are complete. To implement it, you should avoid using static or global variables, and instead use local variables or pass data through function parameters.

Can you give me an example of a reentrant function?

Sure! Here's a simple example of a reentrant function that calculates the factorial of a number:

int factorial(int n) {
    if (n < 0) return 0; // Handle negative input
    if (n == 0) return 1;
    return n * factorial(n - 1);
}

This function is reentrant because it does not use any static or global variables.

What about using mutexes for shared resources?

Using mutexes can help protect shared resources in a multi-threaded environment, but it can make a function non-reentrant. Instead, consider using thread-local storage or passing resources as parameters to maintain reentrancy.

Are there any libraries that help with reentrancy?

Yes, libraries like pthread in C provide mechanisms for thread management and can help you implement reentrant functions. Just ensure that you manage shared resources carefully.