check for pending operations

[swilly22]

This pull-request adds the GxB_Matrix_pending function which checks if a matrix A has any pending work:

1. pending tuples
2. zombies
3. jumbled
4. hyper-hash

In which case the functions sets its input/output argument to true otherwise the argument is set to false.
Please let me know if I should add a test.

[DrTimothyAldenDavis]

I'm still undecided if this should be GxB_Matrix_pending, or if I should use something like:

GxB_get (A, GxB_(something new here), &has_pending_operations) ;

[swilly22]

I don't have a preference in this case.

If there are any guarantees, possible side-effects e.g. GxB_get will never flush the queries object in either one of the different conventions pick the one which suites us best.

[rayegun]

@swilly22 what was the background for this PR? What is your use case? The C committee is discussing it.

[swilly22]

RedisGraph may use a matrix A via multiple threads concurrently.
In case A has pending changes (requires wait) we must avoid concurrent matrix synchronization. Before a thread gains "access" to a matrix it checks for any pending work via GxB_Matrix_pending and if needed synchronize the matrix is a thread safe manner.

[DrTimothyAldenDavis]

I'm getting ready to release GraphBLAS 8.2.2 with some minor updates (in SuiteSparse 7.4), and I'm waiting on the 2.1 C API to be released so that I can release GraphBLAS 9.0.0 with the latest GrB get/set methods.

Kernel fusion might render this method a challenge. I haven't started kernel fusion yet but it would be a problem if I added this method to GraphBLAS now, only to have to take it out when I get to that project.

So for now, let's hold of. It works for now inside FalkorDB and RedisGraph, for GraphBLAS 8.x and 9.x. I hope to keep it in place for GraphBLAS when I add kernel fusion but time will tell.

[swilly22]

Can you please explain how GxB_Matrix_pending is effected by kernel fusion?

[DrTimothyAldenDavis]

Unsure, but I need to somehow flag a matrix as taking part in one or more pending GraphBLAS operations. There's a possibility that keeping GxB_Matrix_pending functional when kernel fusion is added would be complicated, and might need an API change.