Fix JNIVector garbage collection, check if JVM destroyed (#163)

Author: mkitti

src/jniarray.jl

@@ -50,12 +50,21 @@ for primitive in [:jboolean, :jchar, :jbyte, :jshort, :jint, :jlong, :jfloat, :j
     m = quote
         function get_elements!(jarr::JNIVector{$primitive})
             sz = Int(JNI.GetArrayLength(jarr.ref.ptr))
-            jarr.arr = unsafe_wrap(Array, $get_elements(jarr.ref.ptr, Ptr{jboolean}(C_NULL)), sz)
+            # Free the array in release_elements rather than directly via GC
+            jarr.arr = unsafe_wrap(Array, $get_elements(jarr.ref.ptr, Ptr{jboolean}(C_NULL)), sz; own = false)
             jarr
         end
         JNIVector{$primitive}(sz::Int) = get_elements!(JNIVector{$primitive}($new_array(sz)))
         function release_elements(arg::JNIVector{$primitive})
-            $release_elements(arg.ref.ptr, pointer(arg.arr), jint(0))
+            # Make sure that JVM has not been destroyed
+            if JNI.ppenv[1] != C_NULL
+                arr = arg.arr
+                ref = arg.ref
+                # The correct way would be let ccall handle this by removing typing from JNI wrappers
+                GC.@preserve arg ref arr begin
+                    $release_elements(ref.ptr, pointer(arr), jint(0))
+                end
+            end
             arg.arr = nothing
         end
         function convert_result(::Type{JNIVector{$primitive}}, ptr)

test/runtests.jl

@@ -237,7 +237,6 @@ end
 end
 
 @testset "jni_arrays_1" begin
-    #=
     j_u_arrays = @jimport java.util.Arrays
     arr = jint[10,20,30,40,50,60]
     jniarr = JNIVector(arr)
@@ -252,11 +251,13 @@ end
     @test "array" == jcall(buf, "toString", JString, ())
 
     # Ensure JNIVectors are garbage collected properly
-    for i in 1:100000
+    # This used to be 1:100000
+    @info "JNIVector GC test..."
+    for i in 1:1000
         a = JNIVector(jchar[j == i ? 0 : 1 for j in 1:10000])
         buf = jcall(JCharBuffer, "wrap", JCharBuffer, (JNIVector{jchar},), a)
     end
-    =#
+    @info "JNIVector GC test complete."
 end
 
 @testset "dates_1" begin
@@ -451,5 +452,7 @@ catch err
     sprint(showerror, err, backtrace())
 end
 
+# Run GC before we destroy to avoid errors
+GC.gc()
 # At the end, unload the JVM before exiting
 JavaCall.destroy()