diff options
Diffstat (limited to 'src/coins.h')
-rw-r--r-- | src/coins.h | 44 |
1 files changed, 35 insertions, 9 deletions
diff --git a/src/coins.h b/src/coins.h index e71c8a47bc..d5484bcf65 100644 --- a/src/coins.h +++ b/src/coins.h @@ -109,19 +109,45 @@ public: } }; +/** + * A Coin in one level of the coins database caching hierarchy. + * + * A coin can either be: + * - unspent or spent (in which case the Coin object will be nulled out - see Coin.Clear()) + * - DIRTY or not DIRTY + * - FRESH or not FRESH + * + * Out of these 2^3 = 8 states, only some combinations are valid: + * - unspent, FRESH, DIRTY (e.g. a new coin created in the cache) + * - unspent, not FRESH, DIRTY (e.g. a coin changed in the cache during a reorg) + * - unspent, not FRESH, not DIRTY (e.g. an unspent coin fetched from the parent cache) + * - spent, FRESH, not DIRTY (e.g. a spent coin fetched from the parent cache) + * - spent, not FRESH, DIRTY (e.g. a coin is spent and spentness needs to be flushed to the parent) + */ struct CCoinsCacheEntry { Coin coin; // The actual cached data. unsigned char flags; enum Flags { - DIRTY = (1 << 0), // This cache entry is potentially different from the version in the parent view. - FRESH = (1 << 1), // The parent view does not have this entry (or it is pruned). - /* Note that FRESH is a performance optimization with which we can - * erase coins that are fully spent if we know we do not need to - * flush the changes to the parent cache. It is always safe to - * not mark FRESH if that condition is not guaranteed. + /** + * DIRTY means the CCoinsCacheEntry is potentially different from the + * version in the parent cache. Failure to mark a coin as DIRTY when + * it is potentially different from the parent cache will cause a + * consensus failure, since the coin's state won't get written to the + * parent when the cache is flushed. + */ + DIRTY = (1 << 0), + /** + * FRESH means the parent cache does not have this coin or that it is a + * spent coin in the parent cache. If a FRESH coin in the cache is + * later spent, it can be deleted entirely and doesn't ever need to be + * flushed to the parent. This is a performance optimization. Marking a + * coin as FRESH when it exists unspent in the parent cache will cause a + * consensus failure, since it might not be deleted from the parent + * when this cache is flushed. */ + FRESH = (1 << 1), }; CCoinsCacheEntry() : flags(0) {} @@ -246,7 +272,7 @@ public: bool HaveCoinInCache(const COutPoint &outpoint) const; /** - * Return a reference to Coin in the cache, or a pruned one if not found. This is + * Return a reference to Coin in the cache, or coinEmpty if not found. This is * more efficient than GetCoin. * * Generally, do not hold the reference returned for more than a short scope. @@ -258,8 +284,8 @@ public: const Coin& AccessCoin(const COutPoint &output) const; /** - * Add a coin. Set potential_overwrite to true if a non-pruned version may - * already exist. + * Add a coin. Set potential_overwrite to true if an unspent version may + * already exist in the cache. */ void AddCoin(const COutPoint& outpoint, Coin&& coin, bool potential_overwrite); |