Free Synchronization lessonsSynchronization · Stage 1 · Locks and semaphores · Step 1
Locks and atomic instructions
See how a mutex fixes the counter, how hardware makes a lock possible, and when spinning beats sleeping. About 13 minutes.
Why must the lock-acquire operation itself use an atomic instruction such as test-and-set?
- AOtherwise two threads could both see the lock as free and both take it
- BAtomic instructions are the fastest instructions
- CThe OS refuses to run non-atomic code
Show the answer
Otherwise two threads could both see the lock as free and both take it. Checking and setting the lock would be a race of its own.
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