mtchavez/cuckoo

Cuckoo Filter in golang for set membership approximation

cuckoo's Issues

Race Condition When Writing Filter to Disk

I have something similar to this:

package main

import (
  "github.com/mtchavez/cuckoo"
  "sync"
)

type struct Persister {
  filter cuckoo.Filter
  fileName string
  lock sync.Mutex
}

func (p *Persister) Save() {
  p.lock.Lock()
  defer p.lock.Unlock()

  p.filter.Save(p.fileName)
}

I have multiple goroutines attempting to call Persister.Save() after modifications to ensure that changes get persisted.

Since when Filter.Save() returns, there seems to be no guarantee that the data is written to disk, it appears that these goroutines truncate file writes for each other and everything descends into madness with the size of my Filter growing in memory within the program, but flapping in terms of disk file size: I see sizes of 29, 2MiB, 4MiB, and other values between, as these writes appear to be overlapping each other.

I'm not sure what the solution would be at the API level, but providing some way to guarantee consistency would be really helpful. For now, I have refactored my code to offset writes by consistent time periods using time.Ticker.

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