alexander@alexander-home:~/Documents/Test_Dir/Point_Search_GMP$ diff bloom1B.bf bloom1.bf
Binary files bloom1B.bf and bloom1.bf differ
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What did you expect? I looked at your update, and you are simply creating multiple mutexes, one for each thread that runs process_chunk. And locking the entire loop. Basically protecting nothing.

That's not mutexes are for. You only need a single mutex, and you only need to lock the "bf.insert" call, not the entire loop (or else the entire loops will be exclusive).

I'd personally move the mutex to the bloom filter code, and further block only the actual code that accesses data which can potentially be shared (for example, the hashing part probably doesn't need exclusive access).