[#Chainstate-ActivateBestChain]
= xref:Chainstate.adoc[Chainstate]::ActivateBestChain
:relfileprefix: ../
:mrdocs:

Find the best known block, and make it the tip of the block chain. The result is either failure or an activated best chain. pblock is either nullptr or a pointer to a block that is already loaded (to avoid loading it again from disk).

== Synopsis

Declared in `<validation.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
[[requires_capability(0x7f2e1ba842c8), locks_excluded(0x7f2e1ba84398), requires_capability(0x7f2e14563f18), locks_excluded(0x7f2e14563fe8), requires_capability(0x7f2e373bd0c8), locks_excluded(0x7f2e373bd198), requires_capability(0x7f2e36e33d18), locks_excluded(0x7f2e36e33de8)]]
bool
ActivateBestChain(
    xref:BlockValidationState.adoc[BlockValidationState]& state,
    std::shared_ptr<CBlock const> pblock = nullptr);
----

== Description

ActivateBestChain is split into steps (see ActivateBestChainStep) so that we avoid holding cs_main for an extended period of time; the length of this call may be quite long during reindexing or a substantial reorg.

May not be called with cs_main held. May not be called in a validationinterface callback.

Note that if this is called while a snapshot chainstate is active, and if it is called on a validated chainstate whose tip has reached the base block of the snapshot, its execution will take _MINUTES_ while it hashes the UTXO set to verify the assumeutxo value the snapshot was activated with. `cs_main` will be held during this time.

== Return Value

true unless a system error occurred

== Parameters

[cols="1,4"]
|===
| Name| Description
| *state* [in]
| Validation state updated if a system error occurs.
| *pblock* [in]
| Optional already‐loaded block to avoid re‐reading it from disk.
|===


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