Talk:Test-and-set
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The article previously had a paragraph that said
"However, in multiprocessor systems, it is impossible and undesirable to disable interrupts on all processors at the same time; and even with interrupts disabled, two or more processors could be attempting to access the same semaphore's memory at the same time. The test-and-set instruction, allows any processor to atomically test and modify a memory location, preventing such multiple processor collisions. The processor should still disable its interrupts, as in a uniprocessor system, before executing a test-and-set, to prevent a deadlock if another process running on this processor also accesses that semaphore."
I'm pretty sure that last sentence is incorrect, so I deleted it. My understanding is that the test-and-set assembly language instruction cannot be interrupted by any interrupts, including the one that causes a test-switch to another thread running on this processor. Please tell me if that last sentence was correct for any processor. -- DavidCary 05:36, 3 May 2004 (UTC)
It seems a little redundant to have mostly the same text at compare-and-swap -- should we combine them somehow ?
Seems redundant to me too. Test-and-set effectively swaps value in memory with true. If observed from memory bus both do same operations atomically: one read and one write. Main difference in actual CPU instruction test-and-set is that it also sets CPU condition codes accroding the value read from memory (zero or non-zero). I vote for a combination where we first describe atomic swap and then the 'fine graned' version test-and-set. --Jyke 11:55, 17 Jun 2005 (UTC)
Test-and-set should not be merged with compare-and-swap. The two are different. Test-and-set does not always just check for equality and swap if not. Other, more sophisticated tests are possible, such as "if i < 17 then i = 28".
Also, please note that the texts of the two pages are no longer similar.
I am new to Wikipedia and don't have a user name to post.
I think the definition of test-and-set "If the test fails, the value is not set." may have need some correction. According to "Operation System Concepts" By Abraham Silberschatz, etc. , in page 198 about the definition of TestAndSet instruction. The test and set operations are always executed no matter the test fails or not... —Preceding unsigned comment added by 76.17.106.208 (talk) 15:54, 6 October 2007 (UTC)
