refcount

A simple c program that demonstrates one style of reference counting in c.

Building

$ make

If all goes well a sample program in src/refcount will be built. Run the sample program to test things out.

Reference Counting

To allocate memory with reference counting use the ref_alloc function defined in refcount.h. The returned pointer will point to the allocated memory and have the initial reference count set to 1. To increase the reference count call the ref_retain function. To decrease the reference count use the ref_release function. When the reference count reaches zero by calling ref_release the allocated memory will be freed.

If the reference counted object is passed to another thread, the parent thread must call ref_retain on behalf of the new thread before the object is passed. The new thread must call ref_release before terminating.

See refcount.h for details.

Other Functions

• ref_count - gets the current reference count
• ref_pthread_mutex_lock - locks the object mutex
• ref_pthread_mutex_unlock - unlocks the object mutex
• ref_pthread_try_lock - tries the mutex lock for the object
• ref_pthread_create - creates a new thread incrementing the ref count before passing the object to the new thread

The ref_pthread functions are analogous to the pthread functions of the same name. Instead of specifying a mutex to use for lock operations you pass a pointer to the reference counted object and its mutex is used.

See refcount.h for full details

How it Works

When memory is allocated with ref_alloc additional memory is also allocated which is used to store the reference count and a mutex. Calls to ref_retain and ref_release increment and decrement the retain count. Access to the counter are protected by the mutex. The mutex can also be used to protect the data by use the ref_pthread functions.

See refcount.h and refcount.c for details.