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Concurrent Systems/notes/3.md
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@ -110,4 +110,10 @@ unlock() :=
### Safe registers
Atomic R/W and specialized HW primitives provide some form of atomicity. But is it possible to enforce MUTEX without atomicity?
A **MRMW Safe register** is a register that provides READ and
A **MRSW Safe register** is a register that provides READ and WRITE such that:
1. every READ that does not overlap with a WRITE returns the value stored in the register
2. a READ that overlaps with a WRITE can return **any possible value** (of the register domain).
A **MRMW Safe register** behaves like a MRSW safe register, when WRITE operations do not overlap. Otherwise, in case of overlapping WRITEs, the register can contain any value (of the register domain).
This is the weakest type of register that is useful in concurrency.