SYNOPSIS

#include <iv_work.h>

struct iv_work_pool {
int max_threads;
void *cookie;
void (*thread_start)(void *cookie);
void (*thread_stop)(void *cookie);
};
struct iv_work_item {
void *cookie;
void (*work)(void *cookie);
void (*completion)(void *cookie);
};

void IV_WORK_POOL_INIT(struct iv_work_pool *this);
int iv_work_pool_create(struct iv_work_pool *this);
int iv_work_pool_put(struct iv_work_pool *this);
void IV_WORK_ITEM_INIT(struct iv_work_item *work);
int iv_work_pool_submit_work(struct iv_work_pool *this, struct iv_work_item *work);

DESCRIPTION

Calling iv_work_pool_create on a struct iv_work_pool object previously initialised by IV_WORK_POOL_INIT creates a pool of worker threads that can be used to offload CPU intensive tasks to, so as to prevent negatively influencing event handling latency in the calling thread, and to enable the use of multiple host CPUs for CPU intensive tasks.

iv_work dynamically adjusts the number of threads in the pool to the amount of work there is to do. The ->max_threads member of struct iv_work_pool specifies the maximum number of threads that will be created in this pool.

Calling iv_work_pool_submit_work on a struct iv_work_item object previously initialised by IV_WORK_ITEM_INIT submits a work item to a pool. The ->work member of struct iv_work_item specifies the function that will be called in one of the worker threads in the pool specified by ->this, with ->cookie as its sole argument. When the work function has completed, iv_work will call the ->completion callback to indicate this, also with ->cookie as its sole argument, in the thread that iv_work_pool_create was called in for this pool object.

As a special case, calling iv_work_pool_submit_work with a NULL work pool pointer will cause the work item to be processed in the local thread, from an iv_task(3) callback.

If the ->thread_start function pointer specified in struct iv_work_pool is not NULL, it will be called upon creation of a new worker thread, in the context of the created worker thread, with ->cookie as its sole argument. Calls to ->thread_start are not explicitly serialised, which should be kept in mind when manipulating state shared between threads from within that callback function.

Similarly, if iv_work decides to terminate a worker thread, for example due to inactivity, ->thread_stop will be called in the context of the terminating thread, with ->cookie as its sole argument. Calls to ->thread_stop are also not explicitly serialised.

iv_work_pool_submit_work can only be called from the thread that iv_work_pool_create for this pool object was called in.

There is no way to cancel submitted work items.

There is no guaranteed order, FIFO or otherwise, between different work items submitted to the same worker thread pool.

When the user has no more work items to submit to the pool, its reference to the pool can be dropped by calling iv_work_pool_put.

If there are still pending or running work items assigned to this pool when iv_work_pool_put is called, those work items will not be canceled, but will be allowed to run to completion, and their ->completion callbacks will be called as usual. A similar thing holds for the ->thread_start and ->thread_stop callbacks -- they can also still be called after iv_work_pool_put returns. Even so, the memory corresponding to the struct iv_work_pool can immediately be freed or reused by the user upon return of the iv_work_pool_put call.

Internally, iv_work uses iv_thread(3) for its thread management.