docs: pre,begin,end block (#22127)
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Julien Robert
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@@ -232,9 +232,9 @@ The module manager is used throughout the application whenever an action on a co
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* `InitGenesis(ctx context.Context, genesisData map[string]json.RawMessage)`: Calls the [`InitGenesis`](./08-genesis.md#initgenesis) function of each module when the application is first started, in the order defined in `OrderInitGenesis`. Returns an `abci.InitChainResponse` to the underlying consensus engine, which can contain validator updates.
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* `ExportGenesis(ctx context.Context)`: Calls the [`ExportGenesis`](./08-genesis.md#exportgenesis) function of each module, in the order defined in `OrderExportGenesis`. The export constructs a genesis file from a previously existing state, and is mainly used when a hard-fork upgrade of the chain is required.
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* `ExportGenesisForModules(ctx context.Context, modulesToExport []string)`: Behaves the same as `ExportGenesis`, except takes a list of modules to export.
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* `BeginBlock(ctx context.Context) error`: At the beginning of each block, this function is called from [`BaseApp`](../../learn/advanced/00-baseapp.md#beginblock) and, in turn, calls the [`BeginBlock`](./06-beginblock-endblock.md) function of each modules implementing the `appmodule.HasBeginBlocker` interface, in the order defined in `OrderBeginBlockers`. It creates a child [context](../../learn/advanced/02-context.md) with an event manager to aggregate [events](../../learn/advanced/08-events.md) emitted from each modules.
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* `EndBlock(ctx context.Context) error`: At the end of each block, this function is called from [`BaseApp`](../../learn/advanced/00-baseapp.md#endblock) and, in turn, calls the [`EndBlock`](./06-beginblock-endblock.md) function of each modules implementing the `appmodule.HasEndBlocker` interface, in the order defined in `OrderEndBlockers`. It creates a child [context](../../learn/advanced/02-context.md) with an event manager to aggregate [events](../../learn/advanced/08-events.md) emitted from all modules. The function returns an `abci` which contains the aforementioned events, as well as validator set updates (if any).
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* `EndBlock(context.Context) ([]abci.ValidatorUpdate, error)`: At the end of each block, this function is called from [`BaseApp`](../../learn/advanced/00-baseapp.md#endblock) and, in turn, calls the [`EndBlock`](./06-beginblock-endblock.md) function of each modules implementing the `module.HasABCIEndBlock` interface, in the order defined in `OrderEndBlockers`. It creates a child [context](../../learn/advanced/02-context.md) with an event manager to aggregate [events](../../learn/advanced/08-events.md) emitted from all modules. The function returns an `abci` which contains the aforementioned events, as well as validator set updates (if any).
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* `BeginBlock(ctx context.Context) error`: At the beginning of each block, this function is called from [`BaseApp`](../../learn/advanced/00-baseapp.md#beginblock) and, in turn, calls the [`BeginBlock`](./06-preblock-beginblock-endblock.md) function of each modules implementing the `appmodule.HasBeginBlocker` interface, in the order defined in `OrderBeginBlockers`. It creates a child [context](../../learn/advanced/02-context.md) with an event manager to aggregate [events](../../learn/advanced/08-events.md) emitted from each modules.
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* `EndBlock(ctx context.Context) error`: At the end of each block, this function is called from [`BaseApp`](../../learn/advanced/00-baseapp.md#endblock) and, in turn, calls the [`EndBlock`](./06-preblock-beginblock-endblock.md) function of each modules implementing the `appmodule.HasEndBlocker` interface, in the order defined in `OrderEndBlockers`. It creates a child [context](../../learn/advanced/02-context.md) with an event manager to aggregate [events](../../learn/advanced/08-events.md) emitted from all modules. The function returns an `abci` which contains the aforementioned events, as well as validator set updates (if any).
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* `EndBlock(context.Context) ([]abci.ValidatorUpdate, error)`: At the end of each block, this function is called from [`BaseApp`](../../learn/advanced/00-baseapp.md#endblock) and, in turn, calls the [`EndBlock`](./06-preblock-beginblock-endblock.md) function of each modules implementing the `module.HasABCIEndBlock` interface, in the order defined in `OrderEndBlockers`. It creates a child [context](../../learn/advanced/02-context.md) with an event manager to aggregate [events](../../learn/advanced/08-events.md) emitted from all modules. The function returns an `abci` which contains the aforementioned events, as well as validator set updates (if any).
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* `Precommit(ctx context.Context)`: During [`Commit`](../../learn/advanced/00-baseapp.md#commit), this function is called from `BaseApp` immediately before the [`deliverState`](../../learn/advanced/00-baseapp.md#state-updates) is written to the underlying [`rootMultiStore`](../../learn/advanced/04-store.md#commitmultistore) and, in turn calls the `Precommit` function of each modules implementing the `HasPrecommit` interface, in the order defined in `OrderPrecommiters`. It creates a child [context](../../learn/advanced/02-context.md) where the underlying `CacheMultiStore` is that of the newly committed block's [`finalizeblockstate`](../../learn/advanced/00-baseapp.md#state-updates).
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* `PrepareCheckState(ctx context.Context)`: During [`Commit`](../../learn/advanced/00-baseapp.md#commit), this function is called from `BaseApp` immediately after the [`deliverState`](../../learn/advanced/00-baseapp.md#state-updates) is written to the underlying [`rootMultiStore`](../../learn/advanced/04-store.md#commitmultistore) and, in turn calls the `PrepareCheckState` function of each module implementing the `HasPrepareCheckState` interface, in the order defined in `OrderPrepareCheckStaters`. It creates a child [context](../../learn/advanced/02-context.md) where the underlying `CacheMultiStore` is that of the next block's [`checkState`](../../learn/advanced/00-baseapp.md#state-updates). Writes to this state will be present in the [`checkState`](../../learn/advanced/00-baseapp.md#state-updates) of the next block, and therefore this method can be used to prepare the `checkState` for the next block.
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* (Optional) `RegisterLegacyAminoCodec(cdc *codec.LegacyAmino)`: Registers the [`codec.LegacyAmino`s](../../learn/advanced/05-encoding.md#amino) of each of the application module. This function is usually called early on in the [application's construction](../../learn/beginner/00-app-anatomy.md#constructor).
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sidebar_position: 1
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---
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# BeginBlocker and EndBlocker
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# PreBlocker, BeginBlocker and EndBlocker
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:::note Synopsis
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`BeginBlocker` and `EndBlocker` are optional methods module developers can implement in their module. They will be triggered at the beginning and at the end of each block respectively, when the [`BeginBlock`](../../learn/advanced/00-baseapp.md#beginblock) and [`EndBlock`](../../learn/advanced/00-baseapp.md#endblock) ABCI messages are received from the underlying consensus engine.
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`PreBlocker`, `BeginBlocker` and `EndBlocker` are optional methods module developers can implement in their module.
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They will be triggered at the beginning and at the end of each block respectively, when the [`BeginBlock`](../../learn/advanced/00-baseapp.md#beginblock) and [`EndBlock`](../../learn/advanced/00-baseapp.md#endblock) inside within ABCI `FinalizeBlock`
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:::
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:::note Pre-requisite Readings
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@@ -14,11 +15,22 @@ sidebar_position: 1
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:::
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## PreBlocker
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There are two semantics around the new lifecycle method:
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* It runs before the `BeginBlocker` of all modules
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* It can modify consensus parameters in storage, and signal the caller through the return value.
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:::warning
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Modules are required to get the consensus params from the consensus module. Consensus params located in `sdk.Context` were deprecated and should be treated as unsafe. `sdk.Context` is deprecated due to it being a global state within the entire state machine, it has been replaced with `appmodule.Environment`.
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:::
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## BeginBlocker and EndBlocker
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`BeginBlocker` and `EndBlocker` are a way for module developers to add automatic execution of logic to their module. This is a powerful tool that should be used carefully, as complex automatic functions can slow down or even halt the chain.
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In 0.47.0, Prepare and Process Proposal were added that allow app developers to do arbitrary work at those phases, but they do not influence the work that will be done in BeginBlock. If an application required `BeginBlock` to execute prior to any sort of work is done then this is not possible today (0.50.0).
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In 0.47.0, `PrepareProposal` and `ProcessProposal` were added that allow app developers to do arbitrary work at those phases, but they do not influence the work that will be done in `BeginBlock`, nor are they accessible from modules.
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When needed, `BeginBlocker` and `EndBlocker` are implemented as part of the [`HasBeginBlocker`, `HasABCIEndBlocker` and `EndBlocker` interfaces](./01-module-manager.md#appmodule). This means either can be left-out if not required. The `BeginBlock` and `EndBlock` methods of the interface implemented in `module.go` generally defer to `BeginBlocker` and `EndBlocker` methods respectively, which are usually implemented in `abci.go`.
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@@ -28,10 +40,18 @@ The actual implementation of `BeginBlocker` and `EndBlocker` in `abci.go` are ve
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* If needed, they use the `keeper` and `ctx` to trigger state-transitions.
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* If needed, they can emit [`events`](../../learn/advanced/08-events.md) via the `environments`'s `EventManager`.
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A specific method (`UpdateValidators`) is available to return validator updates to the underlying consensus engine in the form of an [`[]appmodule.ValidatorUpdates`](https://github.com/cosmos/cosmos-sdk/blob/07151304e2ec6a185243d083f59a2d543253cb15/core/appmodule/v2/module.go#L87-L101). This is the preferred way to implement custom validator changes.
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A specific method (`UpdateValidators`) is available to return validator updates to the underlying consensus engine in the form of an [`[]appmodule.ValidatorUpdates`](https://github.com/cosmos/cosmos-sdk/blob/07151304e2ec6a185243d083f59a2d543253cb15/core/appmodule/v2/module.go#L87-L101). This is the preferred way to implement custom validator changes (in v1).
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It is possible for developers to define the order of execution between the `BeginBlocker`/`EndBlocker` functions of each of their application's modules via the module's manager `SetOrderBeginBlocker`/`SetOrderEndBlocker` methods. For more on the module manager, click [here](./01-module-manager.md#manager).
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### Implementation
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A module must implement those core interface to make use of the `PreBlocker`, `BeginBlocker` or `EndBlocker` capabilities:
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```go reference
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https://github.com/cosmos/cosmos-sdk/blob/core/v1.0.0-alpha.4/core/appmodule/v2/module.go#L22-L48
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```
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See an example implementation of `BeginBlocker` from the `distribution` module:
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```go reference
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@@ -49,6 +69,3 @@ and an example implementation of `EndBlocker` with validator updates from the `s
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```go reference
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https://github.com/cosmos/cosmos-sdk/blob/v0.52.0-beta.1/x/staking/keeper/abci.go#L12-L17
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```
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<!-- TODO: leaving this here to update docs with core api changes -->
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---
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sidebar_position: 1
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---
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# PreBlocker
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:::note Synopsis
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`PreBlocker` is optional method module developers can implement in their module. They will be triggered before [`BeginBlock`](../../learn/advanced/00-baseapp.md#beginblock).
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:::
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:::note Pre-requisite Readings
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* [Module Manager](./01-module-manager.md)
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:::
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## PreBlocker
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There are two semantics around the new lifecycle method:
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* It runs before the `BeginBlocker` of all modules
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* It can modify consensus parameters in storage, and signal the caller through the return value.
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Modules are required to get the consensus params from the consensus module. Consensus params located in `sdk.Context` were deprecated and should be treated as unsafe. `sdk.Context` is deprecated due to it being a global state within the entire state machine, it has been replaced with `appmodule.Environment`.
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