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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 ...
The OpenMP standard is supported by some compilers, and allows critical sections to be specified using pragmas. The POSIX pthread API provides lock support. [9] Visual C++ provides the synchronize attribute of methods to be synchronized, but this is specific to COM objects in the Windows architecture and Visual C++ compiler. [10]
In C and C++, the volatile keyword was intended to allow C and C++ programs to directly access memory-mapped I/O. Memory-mapped I/O generally requires that the reads and writes specified in source code happen in the exact order specified with no omissions. Omissions or reorderings of reads and writes by the compiler would break the ...
For example, a useful pair of contracts, allowing occupancy to be passed without establishing the invariant, is: wait c: precondition I modifies the state of the monitor postcondition P c signal c precondition (not empty(c) and P c) or (empty(c) and I) modifies the state of the monitor postcondition I (See Howard [4] and Buhr et al. [5] for more.)
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.
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 ...
Due to the semantics of some programming languages, the code generated by the compiler is allowed to update the shared variable to point to a partially constructed object before A has finished performing the initialization. For example, in Java if a call to a constructor has been inlined then the shared variable may immediately be updated once ...