757d692cae
thread_affinity is a good example of a property relevant only to a particular sched_algorithm implementation. In examples/cpp03/migration, introduce an 'affinity' subclass of fiber_properties with a thread_affinity data member. Derive workstealing_round_robin from sched_algorithm_with_properties<affinity> and, as required by that base class, forward awakened() calls to base-class awakened() method. Reimplement workstealing_round_robin's queue from a std::deque to a "by hand" intrusive singly-linked list so we can efficiently remove an arbitrary item. Make steal() method, instead of always popping the last item, scan the list to find the last item willing to migrate (! thread_affinity). From examples/cpp03/migration/workstealing_round_robin.hpp, an example of a user-supplied sched_algorithm implementation, remove all boost/fiber/detail #includes. These should no longer be needed. Change sched_algorithm_with_properties::properties(worker_fiber*) method to accept fiber_base* instead. The original signature was introduced when every sched_algorithm implementation necessarily manipulated worker_fiber* pointers. Now we're intentionally avoiding the need. For the same reason, introduce a fiber_properties::back_ptr typedef so subclasses can opaquely pass such pointers through their own constructor to the base-class constructor.
boost.fiber
boost.fiber provides a framework for micro-/userland-threads (fibers) scheduled cooperativly. The API contains classes and functions to manage and synchronize fibers similiar to boost.thread.
A fiber is able to store the current execution state, including all registers and CPU flags, the instruction pointer, and the stack pointer and later restore this state. The idea is to have multiple execution paths running on a single thread using a sort of cooperative scheduling (threads are preemptively scheduled) - the running fiber decides explicitly when its yields to allow another fiber to run (context switching).
A context switch between threads costs usally thousends of CPU cycles on x86 compared to a fiber switch with less than 100 cycles. A fiber can only run on a single thread at any point in time.
Building: Detailed instructions can be found at https://svn.boost.org/trac/boost/wiki/TryModBoost.