# Problem using graphviz with JNI **URL:** \ **Category:** Dev\ **Created:** [December 28, 2023, 2:24am UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953 "2023-12-28T02:24:57Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![PavelTurk](https://avatars.discourse-cdn.com/v4/letter/p/3be4f8/32.png) [@PavelTurk](https://forum.graphviz.org/u/PavelTurk)\ **Post date:** [December 28, 2023, 2:24am UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/1 "2023-12-28T02:24:57Z")
Hello all, I am a Java developer and I want to use graphviz native libraries with Java. For this I use JNI. This is my C code for JNI method: ```auto (JNIEnv *env, jobject object, jobjectArray arguments) { int argc = env->GetArrayLength(arguments); char *argv[argc]; jstring strings[argc]; for (int i = 0; i < argc; i++) { jstring strArg = (jstring) env->GetObjectArrayElement(arguments, i); const char *charArg = env->GetStringUTFChars(strArg, 0); strings[i] = strArg; argv[i] = (char*) charArg; } GVC_t *gvc = gvContext(); gvParseArgs(gvc, argc, argv); graph_t *g, *prev = NULL; while ((g = gvNextInputGraph(gvc))) { if (prev) { gvFreeLayout(gvc, prev); agclose(prev); } gvLayoutJobs(gvc, g); gvRenderJobs(gvc, g); prev = g; } gvFinalize(gvc); int result = gvFreeContext(gvc); for (int i = 0; i < argc; i++) { env->ReleaseStringUTFChars(strings[i], argv[i]); } return result; } ``` And I have three tests for this method. I can use these test in any order but the following statement is always true - image is generated for first test, image is NOT generated for the second test and JVM crashes for the third test with the following stack: ```auto C [libc.so.6+0x18b6a7] C [libc.so.6+0x7d022] (vfprintf-internal.c:2377) C [libcgraph.so.6.0.0+0x68ed] agerr_va+0xe6 C [libcgraph.so.6.0.0+0x6a15] agerr+0xb9 C [graphvizj+0x5f767] gvNextInputGraph+0xbb ``` From the fact that test order can be different but result is always the same I can conclude that state is somewhere saved between tests. Could anyone say what I am doing wrong and how to fix it? ---
**Author:** ![PavelTurk](https://avatars.discourse-cdn.com/v4/letter/p/3be4f8/32.png) [@PavelTurk](https://forum.graphviz.org/u/PavelTurk)\ **Post date:** [December 28, 2023, 6:51pm UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/2 "2023-12-28T18:51:38Z")
After some tests I created this [issue](https://gitlab.com/graphviz/graphviz/-/issues/2484) . ---
**Author:** ![schmoo2k](https://sea2.discourse-cdn.com/graphviz/user_avatar/forum.graphviz.org/schmoo2k/32/29_2.png) [@schmoo2k](https://forum.graphviz.org/u/schmoo2k)\ **Post date:** [December 29, 2023, 11:59am UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/3 "2023-12-29T11:59:18Z")
FWIW this the code I use when linking natively (not for JNI, but for WebAssembly): Note: `src` is the DOT string and only contains a single graph. ```c GVC_t *gvc = gvContextPlugins(lt_preloaded_symbols, true); agseterr(AGERR); agseterrf(vizErrorf); agreadline(1); Agraph_t *graph = agmemread(src); if (graph) { char *data = NULL; unsigned int length; gvLayout(gvc, graph, engine); gvRenderData(gvc, graph, format, &data, &length); m_result = data; gvFreeRenderData(data); gvFreeLayout(gvc, graph); agclose(graph); } gvFinalize(gvc); gvFreeContext(gvc); ``` ---
**Author:** ![scnorth](https://sea2.discourse-cdn.com/graphviz/user_avatar/forum.graphviz.org/scnorth/32/89_2.png) [@scnorth](https://forum.graphviz.org/u/scnorth)\ **Post date:** [December 29, 2023, 1:16pm UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/4 "2023-12-29T13:16:56Z")
Over in Graphviz issues, it’s pointed out that apparently `gvParseArgs()` has a bug and isn’t reentrant (if people still use that word?) ---
**Author:** ![PavelTurk](https://avatars.discourse-cdn.com/v4/letter/p/3be4f8/32.png) [@PavelTurk](https://forum.graphviz.org/u/PavelTurk)\ **Post date:** [December 29, 2023, 11:46pm UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/5 "2023-12-29T23:46:14Z")
@schmoo2k Could you show full chain from your non C code to Graphviz? I mean you code → … → … → Graphviz wasm. ---
**Author:** ![schmoo2k](https://sea2.discourse-cdn.com/graphviz/user_avatar/forum.graphviz.org/schmoo2k/32/29_2.png) [@schmoo2k](https://forum.graphviz.org/u/schmoo2k)\ **Post date:** [December 30, 2023, 9:26pm UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/6 "2023-12-30T21:26:34Z")
The code is here: [GitHub - GordonSmith/hpcc-js-wasm: HPCC-Systems Web-Assembly (JavaScript)](https://github.com/GordonSmith/hpcc-js-wasm) but its somewhat complicated (and somewhat outdated). Currently it goes like this: 1. You write an IDL file: [hpcc-js-wasm/src-cpp/graphviz/main.idl at WASI\_WIT · GordonSmith/hpcc-js-wasm · GitHub](https://github.com/GordonSmith/hpcc-js-wasm/blob/WASI_WIT/src-cpp/graphviz/main.idl) 2. The IDL file generates additional c++ wrappers and corresponding JavaScript loaders 3. The C++ and generated wrappers get compiled to wasm 4. The generated JavaScript code loads the wasm and wires up all the wasm methods so they can be called from JavaScript. Note: The above has been obsoleted by WASI and WIT Components - which does a similar thing, but in a more “standard” way and isn’t limited to C++ “Guests” and JS “Hosts” ---
**Author:** ![scnorth](https://sea2.discourse-cdn.com/graphviz/user_avatar/forum.graphviz.org/scnorth/32/89_2.png) [@scnorth](https://forum.graphviz.org/u/scnorth)\ **Post date:** [December 31, 2023, 1:22am UTC](https://forum.graphviz.org/t/problem-using-graphviz-with-jni/1953/7 "2023-12-31T01:22:36Z")
I’m not exactly sure what we are trying to figure out now. Over in gitlab, there’s a [merge request](https://gitlab.com/graphviz/graphviz/-/merge_requests/3502) to fix the bug that started this. I believe @PavelTurk then asked if Graphviz was threadsafe, and we said Definitely Not. @PavelTurk said Then what about WASM Graphviz. The example is a single shot, anyway, maybe can’t answer that question.