It is impossible to implement an operation that requires a given consensus number with only operations with a lower consensus number, no matter how many of such operations one uses.[2] Read–modify–write instructions often produce unexpected results when used on I/O devices, as a write operation may not affect the same internal register that would be accessed in a read operation.[3]
This term is also associated with RAID levels that perform actual write operations as atomic read–modify–write sequences.[4] Such RAID levels include RAID 4, RAID 5 and RAID 6.
^"Writing Lock-Free Code: A Corrected Queue" by Herb Sutter: "Compare-and-swap (CAS) is ... widely available ... However, some systems instead provide the equivalently powerful load-linked/store-conditional (LL/SC) instead."
read, modify, write, computer, science, read, modify, write, class, atomic, operations, such, test, fetch, compare, swap, that, both, read, memory, location, write, value, into, simultaneously, either, with, completely, value, some, function, previous, value, . In computer science read modify write is a class of atomic operations such as test and set fetch and add and compare and swap that both read a memory location and write a new value into it simultaneously either with a completely new value or some function of the previous value These operations prevent race conditions in multi threaded applications Typically they are used to implement mutexes or semaphores These atomic operations are also heavily used in non blocking synchronization Maurice Herlihy 1991 ranks atomic operations by their consensus numbers as follows memory to memory move and swap augmented queue compare and swap fetch and cons sticky byte load link store conditional LL SC 1 2n 2 n register assignment 2 test and set swap fetch and add queue stack 1 atomic read and atomic writeIt is impossible to implement an operation that requires a given consensus number with only operations with a lower consensus number no matter how many of such operations one uses 2 Read modify write instructions often produce unexpected results when used on I O devices as a write operation may not affect the same internal register that would be accessed in a read operation 3 This term is also associated with RAID levels that perform actual write operations as atomic read modify write sequences 4 Such RAID levels include RAID 4 RAID 5 and RAID 6 See also editLinearizability Read erase modify writeReferences edit Writing Lock Free Code A Corrected Queue by Herb Sutter Compare and swap CAS is widely available However some systems instead provide the equivalently powerful load linked store conditional LL SC instead Herlihy Maurice January 1991 Wait free synchronization PDF ACM Trans Program Lang Syst 13 1 124 149 CiteSeerX 10 1 1 56 5659 doi 10 1145 114005 102808 S2CID 2181446 Retrieved 2007 05 20 Massmind The read modify write problem Basic RAID Organizations umass edu Archived from the original on 2021 02 24 Retrieved 2013 10 04 nbsp This computer science article is a stub You can help Wikipedia by expanding it vte Retrieved from https en wikipedia org w index php title Read modify write amp oldid 1179530633, wikipedia, wiki, book, books, library,
