CODEWITHSUNDEEP
c++atomicthread-synchronization
Tony The Lion
Tony The Lion

Reputation: 63190

compare and swap vs test and set

Could someone explain to me the working and differences of above operations in multi-threading?

Upvotes: 35

Views: 28134

Answers (2)

Zingphoy Han
Zingphoy Han

Reputation: 119

Test and set operates on a bit, compare and swap operates on a 32-bit field.

The z/TPF system favors the use of the test and set (TS) instruction because frequently, lock indicators are bits that are set to control access to critical regions of system code. The test and set (TS) instruction requires fewer registers than the compare and swap (CS) instruction and requires less execution time because only a single byte needs to be set.

and, I found these materials from : http://www.ibm.com/support/knowledgecenter/SSB23S_1.1.0.13/gtpc3/tasinst.html

you can learn more about TSL with the book called "Modern Operating System,Chapter 2"...

Upvotes: 11

Kirill V. Lyadvinsky
Kirill V. Lyadvinsky

Reputation: 99535

test-and-set modifies the contents of a memory location and returns its old value as a single atomic operation.

compare-and-swap atomically compares the contents of a memory location to a given value and, only if they are the same, modifies the contents of that memory location to a given new value.

The difference marked in bold.

Upvotes: 62

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