Reusing Gurobi environment doesn't work inside package

[pearlzli]

In the past week, reusing a Gurobi environment has stopped working for me inside packages but not modules. I'm using Julia v1.5.3, Gurobi v9.1.1, and Gurobi.jl v0.9.7. As a MWE, I create a package using pkg> generate TestGurobi, add Gurobi as a dependency, and edit src/TestGurobi.jl to be

module TestGurobi

using Gurobi
const GRB_ENV = Gurobi.Env()

end

Then, in the REPL, the Gurobi.Optimizer constructor works with a new Gurobi environment but not with GRB_ENV:

julia> using Gurobi, TestGurobi
[ Info: Precompiling TestGurobi [11fe4acc-459e-4469-9efc-38a933d93789]
Academic license - for non-commercial use only

(TestGurobi) pkg> st Gurobi
Project TestGurobi v0.1.0
Status `~/Desktop/TestGurobi/Project.toml`
  [2e9cd046] Gurobi v0.9.7

julia> Gurobi.Optimizer(Gurobi.Env())
Academic license - for non-commercial use only
    sense  : minimize
    number of variables             = 0
    number of linear constraints    = 0
    number of quadratic constraints = 0
    number of sos constraints       = 0
    number of non-zero coeffs       = 0
    number of non-zero qp objective terms  = 0
    number of non-zero qp constraint terms = 0

julia> Gurobi.Optimizer(TestGurobi.GRB_ENV)
ERROR: Gurobi Error 10002:
Stacktrace:
 [1] _check_ret at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:277 [inlined]
 [2] empty!(::Gurobi.Optimizer) at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:329
 [3] Gurobi.Optimizer(::Gurobi.Env; kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:252
 [4] Gurobi.Optimizer(::Gurobi.Env) at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:225
 [5] top-level scope at REPL[2]:1

However, curiously (in a new REPL session) if I include the module file instead of using the package, GRB_ENV works fine:

julia> using Gurobi; include("src/TestGurobi.jl")
Academic license - for non-commercial use only
Main.TestGurobi

julia> Gurobi.Optimizer(TestGurobi.GRB_ENV)
    sense  : minimize
    number of variables             = 0
    number of linear constraints    = 0
    number of quadratic constraints = 0
    number of sos constraints       = 0
    number of non-zero coeffs       = 0
    number of non-zero qp objective terms  = 0
    number of non-zero qp constraint terms = 0

Defining the constant GRB_ENV in the REPL (again in a new session) directly also works:

julia> using Gurobi

julia> const GRB_ENV = Gurobi.Env()
Academic license - for non-commercial use only
Gurobi.Env(Ptr{Nothing} @0x00007fa5435df800, false, 0)

julia> Gurobi.Optimizer(GRB_ENV)
    sense  : minimize
    number of variables             = 0
    number of linear constraints    = 0
    number of quadratic constraints = 0
    number of sos constraints       = 0
    number of non-zero coeffs       = 0
    number of non-zero qp objective terms  = 0
    number of non-zero qp constraint terms = 0

Am I doing something wrong? I had been using the constant GRB_ENV inside a package for months now without any problems, so I'm not sure what could have changed. I tried updating Gurobi.jl and Gurobi itself, both to the newest versions, to no avail.

[pearlzli]

It seems like there's a weird interaction with Revise.jl (v3.1.11) going on. After executing the first set of REPL commands in my previous post (before "However, curiously..."), if I add an additional line const GRB_ENV_2 = Gurobi.Env() to src/TestGurobi.jl, then I can use GRB_ENV_2 but still not GRB_ENV:

julia> Gurobi.Optimizer(TestGurobi.GRB_ENV_2)
    sense  : minimize
    number of variables             = 0
    number of linear constraints    = 0
    number of quadratic constraints = 0
    number of sos constraints       = 0
    number of non-zero coeffs       = 0
    number of non-zero qp objective terms  = 0
    number of non-zero qp constraint terms = 0


julia> Gurobi.Optimizer(TestGurobi.GRB_ENV)
ERROR: Gurobi Error 10002:
Stacktrace:
 [1] _check_ret at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:277 [inlined]
 [2] empty!(::Gurobi.Optimizer) at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:329
 [3] Gurobi.Optimizer(::Gurobi.Env; kwargs::Base.Iterators.Pairs{Union{},Union{},Tuple{},NamedTuple{(),Tuple{}}}) at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:252
 [4] Gurobi.Optimizer(::Gurobi.Env) at /Users/pearl/.julia/packages/Gurobi/Lci9Q/src/MOI_wrapper.jl:225
 [5] top-level scope at REPL[4]:1

Alternatively, if I rename the constant GRB_ENV to GRB_ENV_3, call Gurobi.Optimizer(TestGurobi.GUROBI_ENV_3), then rename it back to GRB_ENV, then suddenly Gurobi.Optimizer(TestGurobi.GUROBI_ENV) works after all!

[odow]

I can reproduce this. I'll take a look.

[odow]

You can't initialize C variables like this. You need to use an __init__ function like follows:

module TestGurobi

using Gurobi

const GRB_ENV = Ref{Gurobi.Env}()

function __init__()
    global GRB_ENV[] = Gurobi.Env()
end

end

Then

using TestGurobi
env = TestGurobi.GRB_ENV[]

Here are the docs: https://docs.julialang.org/en/v1/manual/modules/#Module-initialization-and-precompilation

[odow]

Closing because this is not an issue with Gurobi.jl.

[pearlzli]

Thanks for the quick response! This worked great for me.