shared_futex | Fast , shared , upgradeable , non-recursive and non-fair mutex

shared_futex is a C++ library. shared_futex has no bugs, it has no vulnerabilities, it has a Permissive License and it has low support. You can download it from GitHub.

Fast, shared, upgradeable, non-recursive and non-fair mutex with support for x86 hardware lock elision via Transactional Synchronization Extensions (TSX). Written in modern cross-platform c++17. In active development. shared_futex encourages a safe RAII interface. Similiarly shared_futex can be locked for shared access. While exclusive locks are mutually exclusive with all other holders, mutiple shared holders are allowed to access the guarded critical section simultaneously. shared_futex can also be locked in upgradeable mode, which allows later to upgrade the lock to an exclusive lock. Upgradeable holders are mutually exclusive with other upgradeable and exclusive locks but not with shared holders. This invariant allows concurrency between shared and upgradeable lockers and, more importantly, ensures that the state of a guarded resource does not change between the upgradeable acquisition and the upgrade to an exclusive lock. In addition, Lock acquisitions attempts can be made with a given time-out. Or in a non-blocking manner via std::try_to_lock. Lock guards can also be manipulated manually. Lock guards meet the requirements of BasicLockable, Lockable and TimedLockable therefore can be used in conjunction with standard library utilities. E.g. avoiding deadlocks when locking multiple mutexes can be done via the standard library's std::lock. Likewise lock guards are default constructible and also meet the requirements of MoveConstructible and MoveAssignable but not of CopyConstructible or CopyAssignable. Therefore lock guards can be safely moved around, swapped and empty assigned via empty brace initialization. Locks can also be adopted. shared_futex default constructor is constexpr therefore a shared_futex is statically initialized making it safe to lock a mutex in the constructor of any static or global object. See c++ initialization order of non-local variables. When an intial lock attempt fails the locking protocol keeps retrying until either a timeout has been reached or lock was successfully acquired. Between iterations a backoff policy is executed. The backoff policy can spin, yield or park the thread.