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package stmtcache
import (
"container/list"
"github.com/jackc/pgx/v5/pgconn"
)
// LRUCache implements Cache with a Least Recently Used (LRU) cache.
type LRUCache struct {
cap int
m map[string]*list.Element
l *list.List
invalidStmts []*pgconn.StatementDescription
}
// NewLRUCache creates a new LRUCache. cap is the maximum size of the cache.
func NewLRUCache(cap int) *LRUCache {
return &LRUCache{
cap: cap,
m: make(map[string]*list.Element),
l: list.New(),
}
}
// Get returns the statement description for sql. Returns nil if not found.
func (c *LRUCache) Get(key string) *pgconn.StatementDescription {
if el, ok := c.m[key]; ok {
c.l.MoveToFront(el)
return el.Value.(*pgconn.StatementDescription)
}
return nil
}
// Put stores sd in the cache. Put panics if sd.SQL is "". Put does nothing if sd.SQL already exists in the cache or
// sd.SQL has been invalidated and HandleInvalidated has not been called yet.
func (c *LRUCache) Put(sd *pgconn.StatementDescription) {
if sd.SQL == "" {
panic("cannot store statement description with empty SQL")
}
if _, present := c.m[sd.SQL]; present {
return
}
// The statement may have been invalidated but not yet handled. Do not readd it to the cache.
for _, invalidSD := range c.invalidStmts {
if invalidSD.SQL == sd.SQL {
return
}
}
if c.l.Len() == c.cap {
c.invalidateOldest()
}
el := c.l.PushFront(sd)
c.m[sd.SQL] = el
}
// Invalidate invalidates statement description identified by sql. Does nothing if not found.
func (c *LRUCache) Invalidate(sql string) {
if el, ok := c.m[sql]; ok {
delete(c.m, sql)
c.invalidStmts = append(c.invalidStmts, el.Value.(*pgconn.StatementDescription))
c.l.Remove(el)
}
}
// InvalidateAll invalidates all statement descriptions.
func (c *LRUCache) InvalidateAll() {
el := c.l.Front()
for el != nil {
c.invalidStmts = append(c.invalidStmts, el.Value.(*pgconn.StatementDescription))
el = el.Next()
}
c.m = make(map[string]*list.Element)
c.l = list.New()
}
// GetInvalidated returns a slice of all statement descriptions invalidated since the last call to RemoveInvalidated.
func (c *LRUCache) GetInvalidated() []*pgconn.StatementDescription {
return c.invalidStmts
}
// RemoveInvalidated removes all invalidated statement descriptions. No other calls to Cache must be made between a
// call to GetInvalidated and RemoveInvalidated or RemoveInvalidated may remove statement descriptions that were
// never seen by the call to GetInvalidated.
func (c *LRUCache) RemoveInvalidated() {
c.invalidStmts = nil
}
// Len returns the number of cached prepared statement descriptions.
func (c *LRUCache) Len() int {
return c.l.Len()
}
// Cap returns the maximum number of cached prepared statement descriptions.
func (c *LRUCache) Cap() int {
return c.cap
}
func (c *LRUCache) invalidateOldest() {
oldest := c.l.Back()
sd := oldest.Value.(*pgconn.StatementDescription)
c.invalidStmts = append(c.invalidStmts, sd)
delete(c.m, sd.SQL)
c.l.Remove(oldest)
}
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