init.cpp:1635 prints mapBlockIndex.size() without cs_main. This is technically a race (though it is rather inconsequential). At some point someone should fix this so tsan stops complaining.
{
    CValidationState state;
    const CChainParams& chainparams = Params();
    FlushStateToDisk(chainparams, state, FLUSH_STATE_NONE, nManualPruneHeight);
}
/**
 * Prune block and undo files (blk???.dat and undo???.dat) so that the disk space used is less than a user-defined target.
 * The user sets the target (in MB) on the command line or in config file.  This will be run on startup and whenever new
 * space is allocated in a block or undo file, staying below the target. Changing back to unpruned requires a reindex
 * (which in this case means the blockchain must be re-downloaded.)
 *
 * Pruning functions are called from FlushStateToDisk when the global fCheckForPruning flag has been set.
 * Block and undo files are deleted in lock-step (when blk00003.dat is deleted, so is rev00003.dat.)
 * Pruning cannot take place until the longest chain is at least a certain length (100000 on mainnet, 1000 on testnet, 1000 on regtest).
 * Pruning will never delete a block within a defined distance (currently 288) from the active chain's tip.
 * The block index is updated by unsetting HAVE_DATA and HAVE_UNDO for any blocks that were stored in the deleted files.
 * A db flag records the fact that at least some block files have been pruned.
 *
 * @param[out]   setFilesToPrune   The set of file indices that can be unlinked will be returned
 */
static void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight)
{
    LOCK2(cs_main, cs_LastBlockFile);
    if (chainActive.Tip() == nullptr || nPruneTarget == 0) {
        return;
    }
    if ((uint64_t)chainActive.Tip()->nHeight <= nPruneAfterHeight) {
        return;
    }
    unsigned int nLastBlockWeCanPrune = chainActive.Tip()->nHeight - MIN_BLOCKS_TO_KEEP;