Add a Worker thread API

[anonymous]

We sometimes use a worker-thread-like service. Each time it is recreated from scratch. Let's add an API for this.

Here is such a proposal

// Skipped GPCT stuff to declare a queue as "worker_internal".

/**
 @this is an item pushable to a worker queue.
 */
struct worker_item_s
{
    worker_internal_item_t item;
};


/**
 @this permits to retrieve an actual structure from an item
 pointer
 */
#define WORKER_ITEM_TO_STRUCT(struct_type, field, item)

/**
 @this is a worker function type definition.

 Function must return once it handled the reason of wakeup.
 */
typedef void worker_func_t(struct worker_item_s *item, void *priv);

struct worker_thread_s
{
    worker_func_t *func;
    void *priv;
    // lock, queue, whatever
};

/***/
void worker_thread_init(struct worker_thread_s*,
                        worker_func_t *func,
                        void *func_priv);

/**
 @this runs a context, i.e. this makes the worker ready for wake
 up. This does not make function to be called
 */
void worker_thread_start(struct worker_thread_s*);

/**
 @this kills the context, but waits for completion of all actions
 pending.
 */
void worker_thread_stop(struct worker_thread_s*);

/**
 @this makes the worker function to be called once. Multiple
 calls to this function yields multiple consecutive calls to
 the worker function.

 @param item The item to pass to the woken-up function
 */
void worker_thread_wakeup(struct worker_thread_s*, struct worker_item_s *item);

Open questions:

• Allow function to sucide worker context