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## Description Closes: #9404 --- ### Author Checklist *All items are required. Please add a note to the item if the item is not applicable and please add links to any relevant follow up issues.* I have... - [x] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title - [ ] added `!` to the type prefix if API or client breaking change - [x] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting)) - [x] provided a link to the relevant issue or specification - [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules) - [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing) - [ ] added a changelog entry to `CHANGELOG.md` - [ ] included comments for [documenting Go code](https://blog.golang.org/godoc) - [ ] updated the relevant documentation or specification - [x] reviewed "Files changed" and left comments if necessary - [x] confirmed all CI checks have passed ### Reviewers Checklist *All items are required. Please add a note if the item is not applicable and please add your handle next to the items reviewed if you only reviewed selected items.* I have... - [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title - [ ] confirmed `!` in the type prefix if API or client breaking change - [ ] confirmed all author checklist items have been addressed - [ ] reviewed state machine logic - [ ] reviewed API design and naming - [ ] reviewed documentation is accurate - [ ] reviewed tests and test coverage - [ ] manually tested (if applicable)
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BeginBlocker and EndBlocker
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 and EndBlock ABCI messages are received from the underlying consensus engine. {synopsis}
Pre-requisite Readings
- Module Manager {prereq}
BeginBlocker and EndBlocker
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.
When needed, BeginBlocker and EndBlocker are implemented as part of the AppModule interface. 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.
The actual implementation of BeginBlocker and EndBlocker in abci.go are very similar to that of a Msg service:
- They generally use the
keeperandctxto retrieve information about the latest state. - If needed, they use the
keeperandctxto trigger state-transitions. - If needed, they can emit
eventsvia thectx'sEventManager.
A specificity of the EndBlocker is that it can return validator updates to the underlying consensus engine in the form of an []abci.ValidatorUpdates. This is the preferred way to implement custom validator changes.
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.
See an example implementation of BeginBlocker from the distr module:
and an example implementation of EndBlocker from the staking module:
Next {hide}
Learn about keepers {hide}