You're looking for
validation.h and its corresponding .cpp source file.
You should start at
CChainState::ActivateBestChain. This subroutine calls
CChainState::ActivateBestChainStep which runs the logic you're interested in - stepping one by one of the blocks, cleaning up and reorg'ing from lowest to highest PoW.
ActivateBestChainStep walks the chain in a
while (m_chain.Tip() && m_chain.Tip() != pindexFork) cleaning up blocks which are not in the best chain using
DisconnectTip(state, chainparams, &disconnectpool). This partly answers your question - all the blocks which aren't in the best chain are weeded out here.
It then walks through the current
CBlockIndex organizing blocks using the next while loop:
while (fContinue && nHeight != pindexMostWork->nHeight).
pindexMostWork is a
CBlockIndex that contains the blocks with most work. Inside there is a loop which selects the blocks it should connect to the best chain:
while (pindexIter && pindexIter->nHeight != nHeight). It pushes the candidate blocks onto a locally allocated vector
Next it iterates this new vector in reverse, pushing the blocks with lowest work first:
for (CBlockIndex *pindexConnect : reverse_iterate(vpindexToConnect)) connecting each to the tip. The last connected block will be the block with the highest work index. This builds a chain sorted from lowest to highest work.
Several places in the code call
ActivateBestChain, among them:
Processmessage in net_processing.cpp
- Several subroutines in
You can use any of the above to trace how and when a new best chain is activated. I think the most interesting ones are in
net_processing.cpp as those are the ones triggered by messages received from the network.