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2e3be68617
This prevents from possible corruption of the internal cache map when the underlying byte slice used by the string key is modified. Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3227
54 lines
1.5 KiB
Go
54 lines
1.5 KiB
Go
package bytesutil
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import (
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"strings"
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"sync"
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"sync/atomic"
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)
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// FastStringMatcher implements fast matcher for strings.
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//
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// It caches string match results and returns them back on the next calls
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// without calling the matchFunc, which may be expensive.
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type FastStringMatcher struct {
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m atomic.Value
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mLen uint64
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matchFunc func(s string) bool
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}
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// NewFastStringMatcher creates new matcher, which applies matchFunc to strings passed to Match()
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//
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// matchFunc must return the same result for the same input.
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func NewFastStringMatcher(matchFunc func(s string) bool) *FastStringMatcher {
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var fsm FastStringMatcher
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fsm.m.Store(&sync.Map{})
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fsm.matchFunc = matchFunc
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return &fsm
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}
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// Match applies matchFunc to s and returns the result.
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func (fsm *FastStringMatcher) Match(s string) bool {
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m := fsm.m.Load().(*sync.Map)
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v, ok := m.Load(s)
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if ok {
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// Fast path - s match result is found in the cache.
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bp := v.(*bool)
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return *bp
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}
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// Slow path - run matchFunc for s and store the result in the cache.
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b := fsm.matchFunc(s)
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bp := &b
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// Make a copy of s in order to limit memory usage to the s length,
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// since the s may point to bigger string.
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// This also protects from the case when s contains unsafe string, which points to a temporary byte slice.
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// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3227
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s = strings.Clone(s)
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m.Store(s, bp)
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n := atomic.AddUint64(&fsm.mLen, 1)
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if n > 100e3 {
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atomic.StoreUint64(&fsm.mLen, 0)
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fsm.m.Store(&sync.Map{})
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}
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return b
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}
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