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package filer
import (
"sync/atomic"
)
type ReaderPattern struct {
isSequentialCounter int64
lastReadStopOffset int64
}
const ModeChangeLimit = 3
// For streaming read: only cache the first chunk
// For random read: only fetch the requested range, instead of the whole chunk
func NewReaderPattern() *ReaderPattern {
return &ReaderPattern{
isSequentialCounter: 0,
lastReadStopOffset: 0,
}
}
func (rp *ReaderPattern) MonitorReadAt(offset int64, size int) {
lastOffset := atomic.SwapInt64(&rp.lastReadStopOffset, offset+int64(size))
counter := atomic.LoadInt64(&rp.isSequentialCounter)
if lastOffset == offset {
if counter < ModeChangeLimit {
atomic.AddInt64(&rp.isSequentialCounter, 1)
}
} else {
if counter > -ModeChangeLimit {
atomic.AddInt64(&rp.isSequentialCounter, -1)
}
}
}
func (rp *ReaderPattern) IsRandomMode() bool {
return atomic.LoadInt64(&rp.isSequentialCounter) < 0
}
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