[Android] Fix Djinni initialization crash in multi shared library case (

#310)

Fix Djinni initialization crash in multi shared library case on Android (i.e. djinni_support_lib is a shared library used by other shared libraries).

Replaced generic static_registration class with non-templatized helpers in JniClassInitializer, which simplifies the code and avoids the issues of multiple instantiations of the same static data.

support-lib/jni/djinni_support.cpp

@@ -28,12 +28,35 @@ namespace djinni {
 // Set only once from JNI_OnLoad before any other JNI calls, so no lock needed.
 static JavaVM * g_cachedJVM;
 
+/*static*/
+JniClassInitializer::registration_vec & JniClassInitializer::get_vec() {
+    static JniClassInitializer::registration_vec m;
+    return m;
+}
+
+/*static*/
+std::mutex & JniClassInitializer::get_mutex() {
+    static std::mutex mtx;
+    return mtx;
+}
+
+/*static*/
+JniClassInitializer::registration_vec JniClassInitializer::get_all() {
+    const std::lock_guard<std::mutex> lock(get_mutex());
+    return get_vec();
+}
+
+JniClassInitializer::JniClassInitializer(std::function<void()> init) {
+    const std::lock_guard<std::mutex> lock(get_mutex());
+    get_vec().push_back(std::move(init));
+}
+
 void jniInit(JavaVM * jvm) {
     g_cachedJVM = jvm;
 
     try {
-        for (const auto & kv : JniClassInitializer::Registration::get_all()) {
-            kv.second->init();
+        for (const auto & initializer : JniClassInitializer::get_all()) {
+            initializer();
         }
     } catch (const std::exception & e) {
         // Default exception handling only, since non-default might not be safe if init

support-lib/jni/djinni_support.hpp

@@ -21,7 +21,7 @@
 #include <memory>
 #include <mutex>
 #include <string>
-#include <unordered_map>
+#include <vector>
 
 #include "../proxy_cache_interface.hpp"
 #include "../djinni_common.hpp"
@@ -165,42 +165,23 @@ void jniThrowAssertionError(JNIEnv * env, const char * file, int line, const cha
     } while(false)
 #define DJINNI_ASSERT(check, env) DJINNI_ASSERT_MSG(check, env, #check)
 
-/*
- * Helper for JniClassInitializer.
- */
-template <class Key, class T>
-class static_registration {
-public:
-    using registration_map = std::unordered_map<Key, T *>;
-    static registration_map get_all() {
-        const std::lock_guard<std::mutex> lock(get_mutex());
-        return get_map();
-    }
-    static_registration(const Key & key, T * obj) : m_key(key) {
-        const std::lock_guard<std::mutex> lock(get_mutex());
-        get_map().emplace(key, obj);
-    }
-    ~static_registration() {
-        const std::lock_guard<std::mutex> lock(get_mutex());
-        get_map().erase(m_key);
-    }
-private:
-    const Key m_key;
-    static registration_map & get_map()   { static registration_map m; return m;   }
-    static std::mutex       & get_mutex() { static std::mutex mtx;     return mtx; }
-};
-
 /*
  * Helper for JniClass. (This can't be a subclass because it needs to not be templatized.)
  */
 class JniClassInitializer {
+
+    using registration_vec = std::vector<std::function<void()>>;
+    static registration_vec get_all();
+
 private:
-    using Registration = static_registration<void *, const JniClassInitializer>;
-    const std::function<void()> init;
-    const Registration reg;
-    JniClassInitializer(const std::function<void()> & init) : init(init), reg(this, this) {}
+
+    JniClassInitializer(std::function<void()> init);
+
     template <class C> friend class JniClass;
     friend void jniInit(JavaVM *);
+
+    static registration_vec & get_vec();
+    static std::mutex       & get_mutex();
 };
 
 /*