k-oli@gmx.de writes:
Am Sonntag, 2. November 2008 00:03:44 schrieb Anthony Williams:
The idea behind using fiber inside a threadpool is, that each worker-thread executes multiple fibers - fiber would yield its execution if future::get() would block (because future is not ready)
Exactly. That's what my prototype does too. My point is that you can do this without fibers too, but you might run out of stack.
Interessting - I'd like to see how the code works. Is it possible to access your prototype?
No, sorry. In future::get(), on a fiber-based thread pool you find a new task/fiber and switch to that if the get() would block. On a simple stack-based thread pool, you just look in the task queue for a new task and run it.
One thing you can do with fibers that you can't easily do with a single stack is switch back to the parent task when the nested task blocks. Doing so allows you to run *other* tasks from the pool if a thread blocks and the task it is waiting for is already running elsewhere. You can also migrate tasks between threads.
That's the way boost.threadpool uses boost.fiber (but fibers are not exchanged between worker-threads -> work-stealing is done only on un-fibered tasks waiting in the local queue of a worker-thread).
Doing either of these requires that the task is prepared for it.
in which sense (sorry I'm not aware of)
Fibers are still tied to a particular thread, so thread-local variables and boost::this_thread::get_id() still return the same value for a nested task. This means that a task that calls future::get() might find that its thread-local variables have been overwritten by a nested task when it resumes. It also means that any data structures keyed by the thread::id may have been altered. Finally, the nested task inherits all the locks of the parent, so it may deadlock if it tries to lock the same mutexes (rather than just block if it is running on a separate thread). Anthony -- Anthony Williams Author of C++ Concurrency in Action | http://www.manning.com/williams Custom Software Development | http://www.justsoftwaresolutions.co.uk Just Software Solutions Ltd, Registered in England, Company Number 5478976. Registered Office: 15 Carrallack Mews, St Just, Cornwall, TR19 7UL, UK