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Now that rqueue_ is an STL-compatible container, priority_scheduler::awakened() can use std::find_if() to search for a context with a lower priority. Now that rqueue_ is an intrusive_list, priority_scheduler::property_change() need not search it: it can simply test with context::ready_is_linked(). Now that it's a doubly-linked list, we can use context::ready_unlink() to unlink. Now that method parameters have been renamed from 'f' to 'ctx', change all references in comments accordingly.
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.
boost.fiber is C++14-only!