Preserve data handed to callbacks with pointer_from_objref

src/C_API.jl

@@ -6,6 +6,12 @@
 # PATH uses the Float64 value 1e20 to represent +infinity.
 const INFINITY = 1e20
 
+const _PRESERVED_CONTEXT = IdDict()
+function _preserved_pointer_from_objref(object)
+    push!(_PRESERVED_CONTEXT, object => true)
+    return pointer_from_objref(object)
+end
+
 ###
 ### License.h
 ###
@@ -62,7 +68,11 @@ end
 function OutputInterface(output_data)
     _C_PRINT = @cfunction(_c_print, Cvoid, (Ptr{Cvoid}, Cint, Ptr{Cchar}))
     _C_FLUSH = C_NULL  # flush argument is optional
-    return OutputInterface(pointer_from_objref(output_data), _C_PRINT, _C_FLUSH)
+    return OutputInterface(
+        _preserved_pointer_from_objref(output_data),
+        _C_PRINT,
+        _C_FLUSH,
+    )
 end
 
 function c_api_Output_SetInterface(o::OutputInterface)
@@ -150,7 +160,7 @@ mutable struct Presolve_Interface
 
     function Presolve_Interface(presolve_data::PresolveData)
         return new(
-            pointer_from_objref(presolve_data),
+            _preserved_pointer_from_objref(presolve_data),
             C_NULL,
             C_NULL,
             C_NULL,
@@ -363,7 +373,7 @@ mutable struct MCP_Interface
         end
 
         return new(
-            pointer_from_objref(interface_data),
+            _preserved_pointer_from_objref(interface_data),
             _C_PROBLEM_SIZE,
             _C_BOUNDS,
             _C_FUNCTION_EVALUATION,
@@ -760,77 +770,73 @@ function solve_mcp(
     @assert length(z) == length(lb) == length(ub)
     out_io = silent ? IOBuffer() : stdout
     output_data = OutputData(out_io)
-    GC.@preserve output_data begin
-        c_api_Output_SetInterface(OutputInterface(output_data))
+    c_api_Output_SetInterface(OutputInterface(output_data))
 
-        n = length(z)
-        if n == 0
-            return MCP_Solved, nothing, nothing
-        end
-        if nnz > typemax(Cint)
-            return MCP_Error, nothing, nothing
-        end
-        o = c_api_Options_Create()
-        c_api_Path_AddOptions(o)
-        c_api_Options_Default(o)
-        m = c_api_MCP_Create(n, nnz)
-        if jacobian_structure_constant
-            c_api_MCP_Jacobian_Structure_Constant(m, true)
-        end
-        if jacobian_data_contiguous
-            c_api_MCP_Jacobian_Data_Contiguous(m, true)
-        end
-        m.id_data = InterfaceData(
-            Cint(n),
-            Cint(nnz),
-            F,
-            J,
-            lb,
-            ub,
-            z,
-            variable_names,
-            constraint_names,
-        )
-        m_interface = MCP_Interface(m.id_data)
-        c_api_MCP_SetInterface(m, m_interface)
-        if jacobian_structure_constant && !isempty(jacobian_linear_elements)
-            m.presolve_data = PresolveData() do nnz, types
-                for i in jacobian_linear_elements
-                    types[i] = PRESOLVE_LINEAR
-                end
-                return
+    n = length(z)
+    if n == 0
+        return MCP_Solved, nothing, nothing
+    end
+    if nnz > typemax(Cint)
+        return MCP_Error, nothing, nothing
+    end
+    o = c_api_Options_Create()
+    c_api_Path_AddOptions(o)
+    c_api_Options_Default(o)
+    m = c_api_MCP_Create(n, nnz)
+    if jacobian_structure_constant
+        c_api_MCP_Jacobian_Structure_Constant(m, true)
+    end
+    if jacobian_data_contiguous
+        c_api_MCP_Jacobian_Data_Contiguous(m, true)
+    end
+    m.id_data = InterfaceData(
+        Cint(n),
+        Cint(nnz),
+        F,
+        J,
+        lb,
+        ub,
+        z,
+        variable_names,
+        constraint_names,
+    )
+    m_interface = MCP_Interface(m.id_data)
+    c_api_MCP_SetInterface(m, m_interface)
+    if jacobian_structure_constant && !isempty(jacobian_linear_elements)
+        m.presolve_data = PresolveData() do nnz, types
+            for i in jacobian_linear_elements
+                types[i] = PRESOLVE_LINEAR
             end
-            presolve_interface = Presolve_Interface(m.presolve_data)
-            c_api_MCP_SetPresolveInterface(m, presolve_interface)
+            return
         end
-        if length(kwargs) > 0
-            mktemp() do path, io
-                println(
-                    io,
-                    "* Automatically generated by PATH.jl. Do not edit.",
-                )
-                for (key, val) in kwargs
-                    println(io, key, " ", val)
-                end
-                close(io)
-                return c_api_Options_Read(o, path)
+        presolve_interface = Presolve_Interface(m.presolve_data)
+        c_api_MCP_SetPresolveInterface(m, presolve_interface)
+    end
+    if length(kwargs) > 0
+        mktemp() do path, io
+            println(io, "* Automatically generated by PATH.jl. Do not edit.")
+            for (key, val) in kwargs
+                println(io, key, " ", val)
             end
+            close(io)
+            return c_api_Options_Read(o, path)
         end
-        c_api_Options_Display(o)
-        info = Information(;
-            generate_output = generate_output,
-            use_start = use_start,
-            use_basics = use_basics,
-        )
-        status = c_api_Path_Solve(m, info)
-    end  # GC.@preserve
+    end
+    c_api_Options_Display(o)
+    info = Information(;
+        generate_output = generate_output,
+        use_start = use_start,
+        use_basics = use_basics,
+    )
+    status = c_api_Path_Solve(m, info)
     X = c_api_MCP_GetX(m)
     # TODO(odow): I don't know why, but manually calling MCP_Destroy was
     # necessary to avoid a segfault on Julia 1.0 when using LUSOL. I guess it's
     # something to do with the timing of when things need to get freed on the
     # PATH side? i.e., MCP_Destroy before other things?
     c_api_MCP_Destroy(m)
     m.ptr = C_NULL
+    empty!(_PRESERVED_CONTEXT)
     return MCP_Termination(status), X, info
 end