vault backup: 2025-03-18 08:34:12

.obsidian/workspace.json

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Concurrent Systems/notes/5 - Software Transactional Memory.md

@@ -33,6 +33,7 @@ Implementation: every transaction uses a local working space
 #### A Logical Clock based STM system
 All the READs perform if no inconsistencies arise, or before any inconsistency
 
+(definizioni in def qua sotto)
 >[!def]
 >Let T be a transaction; its read prefix is formed by all its successful READ before its possible abortion.
 
@@ -108,18 +109,21 @@ VWC allows more transactions to commit -> it is a more liberal property than opa
 
 #### A Vector clock based STM system
 We have m shared MRMW registers; register X is represented by a pair XX, with:
-- XX.val the current value of X
-- XX.depend[1...m] a vector clock s.t.
-	- XX.depend[X] is the sequence number associated with the current value of X
-	- XX.depend[Y] is the sequence number associated with the value of Y on which the current value of X depends from
+- `XX.val` the current value of X
+- `XX.depend[1...m]` a vector clock s.t.
+	- `XX.depend[X]` is the sequence number associated with the current value of X
+		- corresponds to the `date` of the previous algorithm
+	- `XX.depend[Y]` is the sequence number associated with the value of Y on which the current value of X depends from
 - There is a starvation-free lock object associated to the pair
 
-We have n processes; process $p_i$ has
-- for every X, a local copy lc(XX) of the implementation of X
-- $p\_depend_i[1…m]$ s.t. $p\_depend_i[X]$ is the seq.num. of the last val of X (directly or undirectly) known by $p_i$
+So for X, I don't just have to track "who modified X", but also "who modified "Y or Z", if they may have influenced X.
 
-Every transaction T issues by pi has:
-- read_set(T) and write_set(T)
+We have n processes; process $p_i$ has
+- for every X, a local copy `lc(XX)` of the implementation of X
+- $p\_depend_i[1…m]$ s.t. $p\_depend_i[X]$ is the sequence number of the last val of X (directly or indirectly) known by $p_i$
+
+Every transaction T issues by $p_i$ has:
+- `read_set(T)` and `write_set(T)`
 - $t\_depend_{T}[1…m]$ a local copy of $p\_depend_i$ (this is used in the optimistic execution, not to change $p\_depend_{i}$ if T aborts)
 
 ```