path: root/src/jvm/jvm.h

#pragma once

#include "jni.h"
#include <stdbool.h>

struct jvm_string {
   const char *data;
   size_t size;
   bool heap; // if on heap, then `data` should be freed
};

struct jvm_array {
   void *data;
   size_t element_sz, size; // `size` == in elements, `size * element_sz` for bytes
};

struct jvm_class {
   struct jvm_string name;
};

struct jvm_method {
   jclass klass;
   struct jvm_string name, signature;
};

struct jvm_object {
   jclass this_klass;

   union {
      struct jvm_array array;
      struct jvm_method method;
      struct jvm_class klass;
      struct jvm_string string;
   };

   enum jvm_object_type {
      JVM_OBJECT_NONE,
      JVM_OBJECT_OPAQUE,
      JVM_OBJECT_ARRAY,
      JVM_OBJECT_METHOD,
      JVM_OBJECT_CLASS,
      JVM_OBJECT_STRING,
      JVM_OBJECT_LAST,
   } type;
};

struct jvm_native_method {
   struct jvm_method method;
   void *function;
};

struct jvm {
   // [0] object is created on `jvm_init` and it's a class object for defining the class of a class
   // every class object's `this_class` member points back to [0], causing recursion.
   // Every other object or class definition is created lazily as needed, only [0] is special.
   // `jobject`'s we return through JNI are actually (index+1) to this array, not pointers.
   struct jvm_object objects[256];

   // Native methods registered by the application.
   // Nothing special, but there's no need to access this array either really.
   // You can use `jvm_get_native_method` instead.
   struct jvm_native_method methods[255];

   // These hold the function pointers for our JNI implementation.
   struct JNINativeInterface native;
   struct JNIInvokeInterface invoke;

   // JNI's api is weird.. pointer to a reference of a struct, OK!
   // Developers have to dereference these pointers to call methods from an ... reference.
   // NOTE: These are pointers, and JNI interface passes pointers to these pointers!
   JNIEnv env; // points to native
   JavaVM vm; // points to invoke
};

void*
jvm_get_native_method(struct jvm *jvm, const char *klass, const char *method);

void
jvm_release(struct jvm *jvm);

void
jvm_init(struct jvm *jvm);