Bug when hashing a file: Returned hash count is not always the same

[holisticode]

This problem appeared while working on #1185.

To reproduce it, one can run the TestGetAllReferences in swarm/storage/filestore_test.go, which is currently disabled on master due to this bug.

Running that test, the result is sometimes 247, sometimes 248 (which apparently should be the correct number), and sometimes even 246 for splitting a 1000000 bytes file.

This seems like a major bug and should be addressed soon.

[nolash]

The problem is a concurrency issue in your HashExplorer. If you add a mutex and lock the write to the HashExplorer.References array, the test passes every time.

It's hard to tell, but perhaps you also ideally should also call HasherStore.Wait() before you count the References in FileStore.GetAllReferences.

[holisticode]

Closed by ethereum/go-ethereum#19028