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tutorial:transfer-api_transactions [2023/07/19 13:47] – [Nested transactions] technici4ntutorial:transfer-api_transactions [2023/07/19 14:00] (current) – [Nested transactions] technici4n
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 Here is the branching graph for that first example: Here is the branching graph for that first example:
  
-{{https://i.imgur.com/qW0ROX3.png}}+{{:tutorial:transaction_graph_1.png?nolink&400|}}
  
 ==== Nested transactions ==== ==== Nested transactions ====
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 Here is the corresponding graph: Here is the corresponding graph:
  
-{{https://i.imgur.com/n4jZ9FH.png}}+{{:tutorial:transaction_graph_2.png?nolink|}}
  
 === Transaction vs TransactionContext === === Transaction vs TransactionContext ===
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 A ''SnapshotParticipant'' saves copies of its internal state and restores them when required. These copies are referred to as “snapshots”, hence the name. Using a ''SnapshotParticipant'' is generally quite simple: A ''SnapshotParticipant'' saves copies of its internal state and restores them when required. These copies are referred to as “snapshots”, hence the name. Using a ''SnapshotParticipant'' is generally quite simple:
-1. Choose a data type to represent copies of internal state. Usually this will be a record. Here we will use ''Integer''. +  - Choose a data type to represent copies of internal state. Usually this will be a record. Here we will use ''Integer''. 
-2. Extend ''SnapshotParticipant<internal state>''. Here we will add ''extends SnapshotParticipant<Integer>'' to our class. +  - Extend ''SnapshotParticipant<internal state>''. Here we will add ''extends SnapshotParticipant<Integer>'' to our class. 
-3. Implement functions to create copies of the internal state, and restore copies thereof - respectively ''createSnapshot'' and ''readSnapshot''. +  - Implement functions to create copies of the internal state, and restore copies thereof - respectively ''createSnapshot'' and ''readSnapshot''. 
-4. Call ''updateSnapshots(transaction)'' before any change to the internal state.+  - Call ''updateSnapshots(transaction)'' before any change to the internal state.
  
 Let’s start with the following template: Let’s start with the following template:
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 Now that we have been through this background knowledge, here is how the ''SnapshotParticipant'' operates: Now that we have been through this background knowledge, here is how the ''SnapshotParticipant'' operates:
-- When ''updateSnapshots'' is called: +  * When ''updateSnapshots'' is called: 
-  - If we already have a snapshot for this transaction, do nothing. +    * If we already have a snapshot for this transaction, do nothing. 
-  - Otherwise call ''createSnapshot'' to save a snapshot, and add a close callback. +    * Otherwise call ''createSnapshot'' to save a snapshot, and add a close callback. 
-- When a transaction is aborted: +  * When a transaction is aborted: 
-  - We are guaranteed to have a snapshot for that transaction due to how state is managed. +    * We are guaranteed to have a snapshot for that transaction due to how state is managed. 
-  - Call ''readSnapshot'' to revert the state changes. +    * Call ''readSnapshot'' to revert the state changes. 
-- When a transaction is committed: +  * When a transaction is committed: 
-  - If this is an outer (= not nested) transaction, the change is confirmed. +    * If this is an outer (= not nested) transaction, the change is confirmed. 
-    - We know that something probably changed, otherwise we would not have a registered close callback. +      * We know that something probably changed, otherwise we would not have a registered close callback. 
-    - Call ''addOuterCloseCallback''. The callback will call ''onFinalCommit''. +      * Call ''addOuterCloseCallback''. The callback will call ''onFinalCommit''. 
-  - If this is a nested transaction, we need to deal with the snapshot: +    * If this is a nested transaction, we need to deal with the snapshot: 
-    - If the parent transaction already has an older snapshot, discard the more recent snapshot. +      * If the parent transaction already has an older snapshot, discard the more recent snapshot. 
-    - Otherwise the snapshot is moved to the parent transaction.+      * Otherwise the snapshot is moved to the parent transaction.
  
 Hopefully that gives an overview of what is happening under the hood. You should now be ready to read [[https://github.com/FabricMC/fabric/blob/1.20.1/fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/api/transfer/v1/transaction/base/SnapshotParticipant.java|the source code of SnapshotParticipant]]. Hopefully that gives an overview of what is happening under the hood. You should now be ready to read [[https://github.com/FabricMC/fabric/blob/1.20.1/fabric-transfer-api-v1/src/main/java/net/fabricmc/fabric/api/transfer/v1/transaction/base/SnapshotParticipant.java|the source code of SnapshotParticipant]].
  
tutorial/transfer-api_transactions.1689774460.txt.gz · Last modified: 2023/07/19 13:47 by technici4n