1[/ 2 Copyright Oliver Kowalke 2014. 3 Distributed under the Boost Software License, Version 1.0. 4 (See accompanying file LICENSE_1_0.txt or copy at 5 http://www.boost.org/LICENSE_1_0.txt 6] 7 8[section:overview Overview] 9 10__boost_context__ is a foundational library that provides a sort of cooperative 11multitasking on a single thread. By providing an abstraction of the current 12execution state in the current thread, including the stack (with local 13variables) and stack pointer, all registers and CPU flags, and the instruction 14pointer, a execution context represents a specific point in the application's 15execution path. This is useful for building higher-level abstractions, like 16__coroutines__, __coop_threads__ or an equivalent to 17[@http://msdn.microsoft.com/en-us/library/9k7k7cf0%28v=vs.80%29.aspx C# keyword __yield__] 18in C++. 19 20__cc__/__con__ provides the means to suspend the current execution path and to 21transfer execution control, thereby permitting another context to run on the 22current thread. This state full transfer mechanism enables a context to suspend 23execution from within nested functions and, later, to resume from where it was 24suspended. While the execution path represented by a __con__ only runs on a 25single thread, it can be migrated to another thread at any given time. 26 27A [@http://en.wikipedia.org/wiki/Context_switch context switch] between threads 28requires system calls (involving the OS kernel), which can cost more than 29thousand CPU cycles on x86 CPUs. By contrast, transferring control vias 30__cc__/__con__ requires only few CPU cycles because it does not involve system 31calls as it is done within a single thread. 32 33All functions and classes are contained in the namespace __context_ns__. 34 35[note This library requires C++11!] 36 37[important Windows using fcontext_t: turn off global program optimization (/GL) and change /EHsc (compiler 38assumes that functions declared as extern "C" never throw a C++ exception) to /EHs (tells 39compiler assumes that functions declared as extern "C" may throw an exception).] 40 41[endsect] 42