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The memory order is said to be strong or sequentially consistent when either the order of operations cannot change or when such changes have no visible effect on any thread. [1] [4] Conversely, the memory order is called weak or relaxed when one thread cannot predict the order of operations arising from another thread.
Program order guarantees that each process issues a memory request ordered by its program and write atomicity defines that memory requests are serviced based on the order of a single FIFO queue. In relaxing program order, any or all the ordering of operation pairs, write-after-write, read-after-write, or read/write-after-read, can be relaxed.
Modern programming languages like Java therefore implement a memory model. The memory model specifies synchronization barriers that are established via special, well-defined synchronization operations such as acquiring a lock by entering a synchronized block or method. The memory model stipulates that changes to the values of shared variables ...
Mathematically, there is a partial order called the happens-before order over all actions performed by the program. The happens-before order subsumes the program order; if one action occurs before another in the program order, it will occur before the other in the happens-before order. In addition, releases and subsequent acquisitions of locks ...
For example, a second CPU may see memory changes made by the first CPU in a sequence that differs from program order. A program is run via a process which can be multi-threaded (i.e. a software thread such as pthreads as opposed to a hardware thread). Different processes do not share a memory space so this discussion does not apply to two ...
Strong consistency is one of the consistency models used in the domain of concurrent programming (e.g., in distributed shared memory, distributed transactions). [1] The protocol is said to support strong consistency if: All accesses are seen by all parallel processes (or nodes, processors, etc.) in the same order (sequentially)
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In computing, row-major order and column-major order are methods for storing multidimensional arrays in linear storage such as random access memory. The difference between the orders lies in which elements of an array are contiguous in memory. In row-major order, the consecutive elements of a row reside next to each other, whereas the same ...