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Implement basic automatic attachment/detachment of c++ threads to JVM. #405

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Dec 30, 2018
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Implement basic automatic attachment/detachment of c++ threads to JVM. #405

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5a95938
Implement basic automatic attachment/detachment of c++ threads to JVM.
mjmacleod Sep 12, 2018
de3f025
Place assignment outside of define.
mjmacleod Sep 12, 2018
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12 changes: 11 additions & 1 deletion support-lib/jni/djinni_support.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -72,7 +72,17 @@ void jniShutdown() {
JNIEnv * jniGetThreadEnv() {
assert(g_cachedJVM);
JNIEnv * env = nullptr;
const jint get_res = g_cachedJVM->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6);
jint get_res = g_cachedJVM->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6);
#ifdef EXPERIMENTAL_AUTO_CPP_THREAD_ATTACH
if (get_res == JNI_EDETACHED) {
get_res = g_cachedJVM->AttachCurrentThread(&env, nullptr);
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I ran into a problem compiling the pull request using Oracle's JDK. The code compiles if I use Android's jni.h, but if I use jni.h that comes with Oracle's JDK, it fails because the AttachCurrentThread parameters are different. Android expects JNIEnv** whereas the JDK expects void**. I got around it with ifdefs, though I'm still in the process of testing the change at runtime.

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Also ran into a runtime issue with Android on NDK 16b, but NDK 18b works. Desktop Java (1.8) works as well (if you account for the difference in attach current thread parameters).

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@mjmacleod mjmacleod Nov 26, 2018 •
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Would it be sufficient to introduce a compile time error for ndk <18?
It seems to me that as an experimental/optional feature thats off by default it should be fine for it to only work on new ndks going forward.

thread_local struct DetachOnExit {
~DetachOnExit() {
g_cachedJVM->DetachCurrentThread();
}
} detachOnExit;
}
#endif
if (get_res != 0 || !env) {
// :(
std::abort();
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