87551c5419
Highlight predicate condition_variable::wait() method in condition_variable front matter. Rewrite the explanation of wait()'s Precondition. Add a condition_variables subsection about no spurious condition_variable wakeups. Remove "or spuriously" from wakeup conditions in wait*() methods. First pass through "spurious wakeup" section in Rationale. First pass through migration.qbk. Use lock_t throughout work_sharing.cpp, instead of lock_t, lock_count and explicit std::unique_lock<std::mutex> declarations. Unify treatment of main and dispatcher fibers. Clarify thread-safety requirements on sched_algorithm::notify() and suspend_until(). Clarify disable_interruption when rethrowing fiber_interrupted. Consolidate future<T>::get(): returns T whether T is R, R& or void. Mention nesting of disable_interruption (which matters) versus nesting of restore_interruption (which doesn't). Mention that a disable_interruption constructed within the scope of another disable_interruption is a no-op, both itself and when passed to restore_interruption. When packaged_task::operator()() stores a value or an exception, state "as if" by promise::set_value() or set_exception(): the shared state is set ready. Similarly for ~packaged_task() and ~promise() setting broken_promise. Sprinkle links to the Allocator concept, std::allocator and std::allocator_arg_t where referenced. Similarly for StackAllocator. Add more cross-reference links where Fiber classes and methods are mentioned. Also things like std::unique_lock and std::mutex. Clarify error condition for value_pop() when channel is close()d. Since fiber_specific_ptr::release() does not invoke cleanup, it should not throw an exception raised during cleanup.
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!