libboost-fiber1.71-dev 1.71.0-6ubuntu6 (armhf binary) in ubuntu focal

 This package forms part of the Boost C++ Libraries collection.
 .
 Boost.Fiber provides a framework for micro-/userland-threads (fibers)
 scheduled cooperatively. The API contains classes and functions to
 manage and synchronize fibers similarly to standard thread support
 library.
 .
 Each fiber has its own stack.
 .
 A fiber can save 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 cooperative scheduling (versus
 threads, which are preemptively scheduled). The running fiber decides
 explicitly when it should yield to allow another fiber to run
 (context switching). Boost.Fiber internally uses execution_context
 from Boost.Context; the classes in this library manage, schedule and,
 when needed, synchronize those execution contexts. A context switch
 between threads usually costs thousands of CPU cycles on x86,
 compared to a fiber switch with less than a hundred cycles. A fiber
 runs on a single thread at any point in time.