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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.
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 ...
For example, reading a 64-bit value from memory may actually be implemented as two sequential reads of two 32-bit memory locations. If a process has only read the first 32 bits, and before it reads the second 32 bits the value in memory gets changed, it will have neither the original value nor the new value but a mixed-up value.
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)
The syntax of the Python programming language is the set of rules that defines how a Python program will be written and interpreted (by both the runtime system and by human readers). The Python language has many similarities to Perl, C, and Java. However, there are some definite differences between the languages.
A model of a Datalog program P is an interpretation I of P which contains all the ground facts of P, and makes all of the rules of P true in I. Model-theoretic semantics state that the meaning of a Datalog program is its minimal model (equivalently, the intersection of all its models). [4] For example, this program: