Thread Pool API

The thread pool application programming interface (API) uses an object-based design. Each of the following objects is represented by a user-mode data structure:

• A pool object is a set of worker threads that can be used to perform work. Each process can create multiple isolated pools with different characteristics as necessary. There is also a default pool for each process.
• A clean-up group is associated with a set of callback-generating objects. Functions exist to wait on and release all objects that are members of each clean-up group. This frees the application from keeping track of all the objects it has created.
• A work object is assigned to a pool and optionally to a clean-up group. It can be posted, causing a worker thread from the pool to execute its callback. A work object can have multiple posts outstanding; each generates a callback. The post operation cannot fail due to lack of resources.
• A timer object controls the scheduling of callbacks. Each time a timer expires, its callback is posted to its worker pool. Setting a timer cannot fail due to lack of resources.
• A wait object causes a waiter thread to wait on a waitable handle. After the wait is satisfied or the time-out period expires, the waiter thread posts the wait objects' callback to the wait's worker pool. Setting a wait cannot fail due to lack of resources.
• An I/O object associates a file handle with the I/O completion port for the thread pool. When an asynchronous I/O operation completes, a worker thread picks up the status of the operation and calls the I/O object's callback.

The following table describes the features of the original and current thread pool APIs.

Thread Pools

Using the Thread Pool Functions