Что (кто) такое test set thoroughness - определение
![The [[natural numbers]] <math>\mathbb{N}</math> are contained in the [[integers]] <math>\mathbb{Z}</math>, which are contained in the [[rational numbers]] <math>\mathbb{Q}</math>, which are contained in the [[real numbers]] <math>\mathbb{R}</math>, which are contained in the [[complex numbers]] <math>\mathbb{C}</math>](https://commons.wikimedia.org/wiki/Special:FilePath/NumberSetinC.svg?width=200 "The [[natural numbers]] <math>\mathbb{N}</math> are contained in the [[integers]] <math>\mathbb{Z}</math>, which are contained in the [[rational numbers]] <math>\mathbb{Q}</math>, which are contained in the [[real numbers]] <math>\mathbb{R}</math>, which are contained in the [[complex numbers]] <math>\mathbb{C}</math>")
![Sea urchin tests (''[[Coelopleurus exquisitus]]'' on a ''[[Phyllacanthus imperialis]]'').](https://commons.wikimedia.org/wiki/Special:FilePath/Sea urchin tests.jpg?width=200 "Sea urchin tests (''[[Coelopleurus exquisitus]]'' on a ''[[Phyllacanthus imperialis]]'').")
![purple sea urchin]].](https://commons.wikimedia.org/wiki/Special:FilePath/Sea urchin test structure (8340336761).jpg?width=200 "purple sea urchin]].")
![Test of an irregular sea urchin (''[[Echinocardium]]'').](https://commons.wikimedia.org/wiki/Special:FilePath/Echinocardium-fd.jpg?width=200 "Test of an irregular sea urchin (''[[Echinocardium]]'').")
![[[Foraminiferan]]s' tests from the [[Adriatic]] Sea.](https://commons.wikimedia.org/wiki/Special:FilePath/3339e Croatie Pag.jpg?width=200 "[[Foraminiferan]]s' tests from the [[Adriatic]] Sea.")
Википедия
In computer science, the test-and-set instruction is an instruction used to write (set) 1 to a memory location and return its old value as a single atomic (i.e., non-interruptible) operation. The caller can then "test" the result to see if the state was changed by the call. If multiple processes may access the same memory location, and if a process is currently performing a test-and-set, no other process may begin another test-and-set until the first process's test-and-set is finished. A central processing unit (CPU) may use a test-and-set instruction offered by another electronic component, such as dual-port RAM; a CPU itself may also offer a test-and-set instruction.
A lock can be built using an atomic test-and-set instruction as follows:
This code assumes that the memory location was initialized to 0 at some point prior to the first test-and-set. The calling process obtains the lock if the old value was 0, otherwise the while-loop spins waiting to acquire the lock. This is called a spinlock. At any point, the holder of the lock can simply set the memory location back to 0 to release the lock for acquisition by another--this does not require any special handling as the holder "owns" this memory location. "Test and test-and-set" is another example.
Maurice Herlihy (1991) proved that test-and-set (1-bit comparand) has a finite consensus number and can solve the wait-free consensus problem for at-most two concurrent processes. In contrast, compare-and-swap (32-bit comparand) offers a more general solution to this problem, and in some implementations compare-double-and-swap (64-bit comparand) is also available for extended utility.
