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cacheMergeIterator #298
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cacheMergeIterator #298
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Original file line number | Diff line number | Diff line change |
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package store | ||
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// TODO: Consider merge w/ tendermint/tmlibs/db/cachedb.go. | ||
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import ( | ||
"bytes" | ||
"sort" | ||
"sync" | ||
"sync/atomic" | ||
) | ||
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// If value is nil but deleted is false, it means the parent doesn't have the | ||
// key. (No need to delete upon Write()) | ||
type cValue struct { | ||
value []byte | ||
deleted bool | ||
dirty bool | ||
} | ||
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// cacheIterKVStore wraps an in-memory cache around an underlying IterKVStore. | ||
type cacheIterKVStore struct { | ||
mtx sync.Mutex | ||
cache map[string]cValue | ||
parent IterKVStore | ||
lockVersion interface{} | ||
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cwwMutex | ||
} | ||
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var _ CacheIterKVStore = (*cacheIterKVStore)(nil) | ||
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// Users should typically not be required to call NewCacheIterKVStore directly, as the | ||
// IterKVStore implementations here provide a .CacheIterKVStore() function already. | ||
// `lockVersion` is typically provided by parent.GetWriteLockVersion(). | ||
func NewCacheIterKVStore(parent IterKVStore, lockVersion interface{}) *cacheIterKVStore { | ||
ci := &cacheIterKVStore{ | ||
cache: make(map[string]cValue), | ||
parent: parent, | ||
lockVersion: lockVersion, | ||
cwwMutex: NewCWWMutex(), | ||
} | ||
return ci | ||
} | ||
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func (ci *cacheIterKVStore) Get(key []byte) (value []byte) { | ||
ci.mtx.Lock() | ||
defer ci.mtx.Unlock() | ||
ci.assertValidKey(key) | ||
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cacheValue, ok := ci.cache[string(key)] | ||
if !ok { | ||
value = ci.parent.Get(key) | ||
ci.setCacheValue(key, value, false, false) | ||
} else { | ||
value = cacheValue.value | ||
} | ||
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return value | ||
} | ||
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func (ci *cacheIterKVStore) Set(key []byte, value []byte) { | ||
ci.mtx.Lock() | ||
defer ci.mtx.Unlock() | ||
ci.assertValidKey(key) | ||
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ci.setCacheValue(key, value, false, true) | ||
} | ||
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func (ci *cacheIterKVStore) Has(key []byte) bool { | ||
value := ci.Get(key) | ||
return value != nil | ||
} | ||
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func (ci *cacheIterKVStore) Remove(key []byte) { | ||
ci.mtx.Lock() | ||
defer ci.mtx.Unlock() | ||
ci.assertValidKey(key) | ||
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ci.setCacheValue(key, nil, true, true) | ||
} | ||
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// Write writes pending updates to the parent database and clears the cache. | ||
// NOTE: Not atomic. | ||
func (ci *cacheIterKVStore) Write() { | ||
ci.mtx.Lock() | ||
defer ci.mtx.Unlock() | ||
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// Optional sanity check to ensure that cacheIterKVStore is valid | ||
if parent, ok := ci.parent.(WriteLocker); ok { | ||
if parent.TryWriteLock(ci.lockVersion) { | ||
// All good! | ||
} else { | ||
panic("parent.Write() failed. Did this CacheIterKVStore expire?") | ||
} | ||
} | ||
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// We need a copy of all of the keys. | ||
// Not the best, but probably not a bottleneck depending. | ||
keys := make([]string, 0, len(ci.cache)) | ||
for key, dbValue := range ci.cache { | ||
if dbValue.dirty { | ||
keys = append(keys, key) | ||
} | ||
} | ||
sort.Strings(keys) | ||
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// TODO in tmlibs/db we use Batch to write atomically. | ||
// Consider locking the underlying IterKVStore during write. | ||
for _, key := range keys { | ||
cacheValue := ci.cache[key] | ||
if cacheValue.deleted { | ||
ci.parent.Remove([]byte(key)) | ||
} else if cacheValue.value == nil { | ||
// Skip, it already doesn't exist in parent. | ||
} else { | ||
ci.parent.Set([]byte(key), cacheValue.value) | ||
} | ||
} | ||
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// Clear the cache | ||
ci.cache = make(map[string]cValue) | ||
} | ||
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//---------------------------------------- | ||
// To cache-wrap this cacheIterKVStore further. | ||
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func (ci *cacheIterKVStore) CacheWrap() CacheWrap { | ||
return ci.CacheIterKVStore() | ||
} | ||
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func (ci *cacheIterKVStore) CacheKVStore() CacheKVStore { | ||
return ci.CacheIterKVStore() | ||
} | ||
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func (ci *cacheIterKVStore) CacheIterKVStore() CacheIterKVStore { | ||
return NewCacheIterKVStore(ci, ci.GetWriteLockVersion()) | ||
} | ||
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// If the parent parent DB implements this, (e.g. such as a cacheIterKVStore | ||
// parent to a cacheIterKVStore child), cacheIterKVStore will call | ||
// `parent.TryWriteLock()` before attempting to write. | ||
// This prevents multiple siblings from Write'ing to the parent. | ||
type WriteLocker interface { | ||
GetWriteLockVersion() (lockVersion interface{}) | ||
TryWriteLock(lockVersion interface{}) bool | ||
} | ||
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// Implements TryWriteLocker. Embed this in DB structs if desired. | ||
type cwwMutex struct { | ||
mtx sync.Mutex | ||
// CONTRACT: reading/writing to `*written` should use `atomic.*`. | ||
// CONTRACT: replacing `written` with another *int32 should use `.mtx`. | ||
written *int32 | ||
} | ||
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func NewCWWMutex() cwwMutex { | ||
return cwwMutex{ | ||
written: new(int32), | ||
} | ||
} | ||
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func (cww *cwwMutex) GetWriteLockVersion() interface{} { | ||
cww.mtx.Lock() | ||
defer cww.mtx.Unlock() | ||
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// `written` works as a "version" object because it gets replaced upon | ||
// successful TryWriteLock. | ||
return cww.written | ||
} | ||
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func (cww *cwwMutex) TryWriteLock(version interface{}) bool { | ||
cww.mtx.Lock() | ||
defer cww.mtx.Unlock() | ||
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if version != cww.written { | ||
return false // wrong "WriteLockVersion" | ||
} | ||
if !atomic.CompareAndSwapInt32(cww.written, 0, 1) { | ||
return false // already written | ||
} | ||
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// New "WriteLockVersion" | ||
cww.written = new(int32) | ||
return true | ||
} | ||
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//---------------------------------------- | ||
// Iteration | ||
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func (ci *cacheIterKVStore) Iterator(start, end []byte) Iterator { | ||
return ci.iterator(start, end, true) | ||
} | ||
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func (ci *cacheIterKVStore) ReverseIterator(start, end []byte) Iterator { | ||
return ci.iterator(start, end, false) | ||
} | ||
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func (ci *cacheIterKVStore) iterator(start, end []byte, ascending bool) Iterator { | ||
var parent, cache Iterator | ||
if ascending { | ||
parent = ci.parent.Iterator(start, end) | ||
} else { | ||
parent = ci.parent.ReverseIterator(start, end) | ||
} | ||
items := ci.dirtyItems(ascending) | ||
cache = newMemIterator(start, end, items) | ||
return newCacheMergeIterator(parent, cache, ascending) | ||
} | ||
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func (ci *cacheIterKVStore) First(start, end []byte) (kv KVPair, ok bool) { | ||
return iteratorFirst(ci, start, end) | ||
} | ||
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func (ci *cacheIterKVStore) Last(start, end []byte) (kv KVPair, ok bool) { | ||
return iteratorLast(ci, start, end) | ||
} | ||
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// Constructs a slice of dirty items, to use w/ memIterator. | ||
func (ci *cacheIterKVStore) dirtyItems(ascending bool) []KVPair { | ||
items := make([]KVPair, 0, len(ci.cache)) | ||
for key, cacheValue := range ci.cache { | ||
if !cacheValue.dirty { | ||
continue | ||
} | ||
items = append(items, | ||
KVPair{[]byte(key), cacheValue.value}) | ||
} | ||
sort.Slice(items, func(i, j int) bool { | ||
if ascending { | ||
return bytes.Compare(items[i].Key, items[j].Key) < 0 | ||
} else { | ||
return bytes.Compare(items[i].Key, items[j].Key) > 0 | ||
} | ||
}) | ||
return items | ||
} | ||
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//---------------------------------------- | ||
// etc | ||
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func (ci *cacheIterKVStore) assertValidKey(key []byte) { | ||
if key == nil { | ||
panic("key is nil") | ||
} | ||
} | ||
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// Only entrypoint to mutate ci.cache. | ||
func (ci *cacheIterKVStore) setCacheValue(key, value []byte, deleted bool, dirty bool) { | ||
cacheValue := cValue{ | ||
value: value, | ||
deleted: deleted, | ||
dirty: dirty, | ||
} | ||
ci.cache[string(key)] = cacheValue | ||
} |
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make an issue & link it in the code
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I'll actually just do the whole thing. 1 moment...