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However, they differ in how they are used. While a binary semaphore may be colloquially referred to as a mutex, a true mutex has a more specific use-case and definition, in that only the task that locked the mutex is supposed to unlock it. This constraint aims to handle some potential problems of using semaphores:
In computer science, a semaphore is a variable or abstract data type used to control access to a common resource by multiple threads and avoid critical section problems in a concurrent system such as a multitasking operating system. Semaphores are a type of synchronization primitive. A trivial semaphore is a plain variable that is changed (for ...
Poco::RWLock in POCO C++ Libraries; mse::recursive_shared_timed_mutex in the SaferCPlusPlus library is a version of std::shared_timed_mutex that supports the recursive ownership semantics of std::recursive_mutex. txrwlock.ReadersWriterDeferredLock Readers/Writer Lock for Twisted [19] rw_semaphore in the Linux kernel [20]
In computing, a futex (short for "fast userspace mutex") is a kernel system call that programmers can use to implement basic locking, or as a building block for higher-level locking abstractions such as semaphores and POSIX mutexes or condition variables. A futex consists of a kernel-space wait queue that is attached to an atomic integer in ...
To enter a critical section, a thread must obtain a semaphore, which it releases on leaving the section. Other threads are prevented from entering the critical section at the same time as the original thread, but are free to gain control of the CPU and execute other code, including other critical sections that are protected by different semaphores.
There are several possible solutions, but all solutions require a mutex, which ensures that only one of the participants can change state at once.The barber must acquire the room status mutex before checking for customers and release it when they begin either to sleep or cut hair; a customer must acquire it before entering the shop and release it once they are sitting in a waiting room or ...
With priority ceiling protocol, the shared mutex process (that runs the operating system code) has a characteristic (high) priority of its own, which is assigned to the task of locking the mutex. This works well, provided the other high-priority task(s) that tries to access the mutex does not have a priority higher than the ceiling priority.
This feature is built into some mutex implementations, for example in glibc. The Hardware Lock Elision (HLE) in x86 is a weakened but backwards-compatible version of TSE, and we can use it here for locking without losing any compatibility.