Segfault upon destruction using hashmap of hashmaps

[charlesgregory]

Segfault upon destruction using hashmap of hashmaps

[jblachly]

Code LGTM, probably you are seeing a double-free since I did not disable copies.
If you @disable this(this) and then attempt your test you should see a compilation failure indicating that a copy is not allowed. Can you confirm this?

[jblachly]

If you confirm this is the problem I will either disable copies or add copy constructor since that is a relatively new feature in Dlang

[charlesgregory]

Yes disabling copies provides me with a long list of compilation errors.

[jblachly]

@charlesgregory can you please provide example code of how you are using nested hashmaps to better understand how we can work around this? I am in favor of disabling copies, but we could potentially instead do refcounting

[charlesgregory]

auto kmers = khash!(string, khash!(string, int))();

 for loop {
    string kmer1;
    string kmer2;

    // if kmer1 not present create empty hashmap
    // initval is empty hashmap
    kmers.require(kmer1, khash!(string, int)()); // <- segfault when kfrees are commented out

    // if kmer2 not present make count zero
    kmers[kmer1].require(kmer2, 0);
  
    kmers[kmer1][kmer2]++;

}

This could potentially be solved by having special compile time checks for a value type that is another khash instance. Might be difficult.

[jblachly]

Yeah you are constructing the object in the parameter position and it is copied into the function.

[jblachly]

Changing the ctor function signature value parameter to include auto ref may fix this although ia m not sure whether should do that or write copy constructor (or both)