Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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Boost.Context is a foundational library that provides a sort of cooperative multitasking on a single thread. By providing an abstraction of the current execution state in the current thread, including the stack (with local variables) and stack pointer, all registers and CPU flags, and the instruction pointer, a fcontext_t instance represents a specific point in the application's execution path. This is useful for building higher-level abstractions, like coroutines, cooperative threads (userland threads) or an aquivalent to C# keyword yield in C++.

A fcontext_t provides the means to suspend the current execution path and to transfer execution control, thereby permitting another fcontext_t to run on the current thread. This stateful transfer mechanism enables a fcontext_t to suspend execution from within nested functions and, later, to resume from where it was suspended. While the execution path represented by a fcontext_t only runs on a single thread, it can be migrated to another thread at any given time.

A context switch between threads requires system calls (involving the OS kernel), which can cost more than thousand CPU cycles on x86 CPUs. By contrast, transferring control among them requires only fewer than hundred CPU cycles because it does not involve system calls as it is done within a single thread.

In order to use the classes and functions described here, you can either include the specific headers specified by the descriptions of each class or function, or include the master library header:

#include <boost/context/all.hpp>

which includes all the other headers in turn.

All functions and classes are contained in the namespace boost::ctx.