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Bad use of package global causes data race, clobbered chunkers #4

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calmh opened this issue Oct 5, 2020 · 0 comments
Open

Bad use of package global causes data race, clobbered chunkers #4

calmh opened this issue Oct 5, 2020 · 0 comments

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@calmh
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calmh commented Oct 5, 2020

Hi! Thanks for this implementation!

I noticed that while it looks like NewChunker returns a new chunker based on the given options, it actually depends on the global table variable, meaning two chunkers with different seed values will stomp on each other, and chunkers cannot be constructed concurrently without causing a data race.

WARNING: DATA RACE
Read at 0x00000594c720 by goroutine 163:
  github.com/jotfs/fastcdc-go.NewChunker()
      /Users/jb/go/pkg/mod/github.com/jotfs/fastcdc-go@v0.2.0/fastcdc.go:110 +0x124
...

Previous write at 0x00000594c720 by goroutine 206:
  github.com/jotfs/fastcdc-go.NewChunker()
      /Users/jb/go/pkg/mod/github.com/jotfs/fastcdc-go@v0.2.0/fastcdc.go:110 +0x155
...
calmh added a commit to kastelo-labs/fastcdc-go that referenced this issue Oct 5, 2020
@calmh
Don't change the global table variable (fixes jotfs#4)
21dff88 
Instead copy it when we want to use a new seed.

Fixes the example test which in fact had incorrect output when run on
its own, depending on the old behavior of someone else having clobbered
the global table previously.
pbtrung added a commit to pbtrung/fastcdc-go that referenced this issue Dec 22, 2020
@pbtrung
Don't change the global table variable (fixes jotfs#4)
6229c7c
pbtrung added a commit to pbtrung/fastcdc-go that referenced this issue Dec 22, 2020
@pbtrung
Don't change the global table variable (fixes jotfs#4)
8edf791
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@calmh