Use atomics for thread safety

Author: ericphanson

src/Convex.jl

@@ -34,15 +34,36 @@ export Positive, Negative, ComplexSign, NoSign
 # Problems
 export add_constraint!, add_constraints!, maximize, minimize, Problem, satisfy, solve!
 
+
+# Module level globals
+
 """
-    const DCP_WARNINGS = Ref(true)
+    DCP_WARNINGS
 
 Controls whether or not warnings are emitted for when an expression fails to be
 of disciplined convex form. To turn warnings off, run
 
     Convex.DCP_WARNINGS[] = false
 """
-const DCP_WARNINGS = Ref(true)
+const DCP_WARNINGS = Threads.Atomic{Bool}(true)
+
+"""
+    MAXDEPTH
+
+Controls depth of tree printing globally for Convex.jl; defaults to 3. Set via
+
+    Convex.MAXDEPTH[] = 5
+"""
+const MAXDEPTH = Threads.Atomic{Int}(3)
+
+"""
+    MAXWIDTH
+
+Controls width of tree printing globally for Convex.jl; defaults to 15. Set via
+
+    Convex.MAXWIDTH[] = 15
+"""
+const MAXWIDTH= Threads.Atomic{Int}(15)
 
 ### modeling framework
 include("dcp.jl")

src/utilities/show.jl

@@ -1,20 +1,6 @@
 import Base.show, Base.summary
 using .TreePrint
 
-"""
-    const MAXDEPTH = Ref(3)
-
-Controls depth of tree printing globally for Convex.jl
-"""
-const MAXDEPTH = Ref(3)
-
-"""
-    const MAXWIDTH = Ref(15)
-
-Controls width of tree printing globally for Convex.jl
-"""
-const MAXWIDTH= Ref(15)
-
 
 """
     show_id(io::IO, x::Union{AbstractExpr, Constraint}; digits = 3)