为什么需要释放在JNI本机函数中创建的全局引用？
我有一个Java类，具有使用C
++实现的本机函数，称为nz.ac.unitec.BigInteger。的本机实现nz.ac.unitec.BigInteger很简单，只是包裹java.math.BigInteger，并调用它的构造函数和add，subtract，multiply…功能。一个字段mNativeContext中nz.ac.unitec.BigInteger用于存储的全局引用一个java.math.BigInteger对象。该对象具有终结器，该终结器应该在垃圾回收对象时破坏全局引用，因此我不会泄漏全局引用。
当我运行一个简单的测试循环以创建多个nz.ac.unitec.BigInteger对象而不显式释放所创建的对象时，在日志（LOG1）之后报告了JNI错误。但是，如果我在离开测试功能之前显式释放创建的对象，则压力测试可以成功执行。
当我有终结器要在垃圾回收对象中删除它们时，为什么JVM的全局引用用完了？
LOG1：
F/art (10730): art/runtime/indirect_reference_table.cc:113] JNI ERROR (app bug): global reference table overflow (max=51200)F/art (10730): art/runtime/indirect_reference_table.cc:113] global reference table dump:
F/art (10730): art/runtime/indirect_reference_table.cc:113] Last 10 entries (of 51200):
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51199: 0x12e88790 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51198: 0x12e85490 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51197: 0x12e81790 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51196: 0x12e7e760 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51195: 0x12e7ab20 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51194: 0x12e77790 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51193: 0x12e73a90 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51192: 0x12e71af0 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51191: 0x12e6dd60 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] 51190: 0x12e6b9a0 java.math.BigInteger
F/art (10730): art/runtime/indirect_reference_table.cc:113] Summary:
F/art (10730): art/runtime/indirect_reference_table.cc:113] 1456 of java.math.BigInteger (1456 unique instances)
F/art (10730): art/runtime/indirect_reference_table.cc:113] 2 of android.opengl.EGLDisplay (2 unique instances)
F/art (10730): art/runtime/indirect_reference_table.cc:113] 1889 of java.math.BigInteger (1889 unique instances)
F/art (10730): art/runtime/indirect_reference_table.cc:113] 1 of java.lang.String
F/art (10730): art/runtime/indirect_reference_table.cc:113] 27 of java.math.BigInteger (27 unique instances)
F/art (10730): art/runtime/indirect_reference_table.cc:113] 1 of java.lang.String
F/art (10730): art/runtime/indirect_reference_table.cc:113] 3771 of java.math.BigInteger (3771 unique instances)
F/art (10730): art/runtime/indirect_reference_table.cc:113] 1 of dalvik.system.PathClassLoader
F/art (10730): art/runtime/runtime.cc:284] Runtime aborting...
F/art (10730): art/runtime/runtime.cc:284] Aborting thread:
计算器.java
package nz.ac.unitec.calculator;public class MainActivity extends AppCompatActivity
{
protected void onCreate(Bundle savedInstanceState)
{
Random ra = new Random();
for(int i=0; i<6000000; ++i) {
testCreateFinalize(ra);
int m = ra.nextInt();
int n = 8;
int re = m + n;
Log.i("MainActivity", "re=" + re);
//BigInteger result = l.subtract(r);
}
private void testCreateFinalize(Random ra)
{
BigInteger l = new BigInteger("100", 10);
BigInteger r = new BigInteger("200", 10);
//l.release(); when adding this two code lines, the test is ok
//r.release();;
}
}
BigInteger.java
package nz.ac.unitec.mathutils;public class BigInteger
{
static {
System.loadLibrary("BigInteger_jni");
native_init();
}
private long mNativeContext;
private BigInteger()
{
mNativeContext = 0;
native_setup();
}
public BigInteger(String val, int radix)
{
mNativeContext = 0;
native_setup_bystring(val, radix);
}
public void release() {
native_finalize();
}
protected void finalize() {
native_finalize();
}
private static native final void native_init();
private native final void native_setup();
private native final void native_setup_bystring(String val, int radix);
private native final void native_finalize();
public native String toString(int radix);
public native BigInteger add(BigInteger rval);
public native BigInteger multiply(BigInteger rval);
public native BigInteger subtract(BigInteger rval);
}
本机代码
static jobject getNativeBigInteger_l(JNIEnv* env, jobject thiz){
return reinterpret_cast<jobject> (env->GetLongField(thiz, fields.context)); //reinterpret_cast<jobject>
}
static void setNativeBigInteger_l(JNIEnv* env, jobject thiz, jobject bi)
{
env->SetLongField(thiz, fields.context, reinterpret_cast<jlong>(bi)); //reinterpret_cast<jlong>
}
JNIEXPORT void JNICALL Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring
(JNIEnv *env, jobject thiz, jstring val, jint radix)
{
jclass cls = env->FindClass(gBuiltinClassBigInteger);
ALOGV("-Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring env->FindClass(%s) return (%0x)",
gBuiltinClassBigInteger, cls);
if (cls == NULL) {
ALOGE("-Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring env->FindClass(%s) return NULL", gBuiltinClassBigInteger);
return;
}
jmethodID constructor = env->GetMethodID(cls, "<init>", "(Ljava/lang/String;I)V");
if (constructor == NULL) {
env->DeleteLocalRef(cls);
ALOGE("-Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring env->GetMethodID(%s) return NULL", "<init>");
return;
}
jobject jobj = env->NewObject(cls, constructor, val, radix);
ALOGV("-Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring env->NewObject return (%0x)",
jobj);
if (NULL == jobj) {
env->DeleteLocalRef(cls);
ALOGE("-Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring env->NewObject return NULL");
return;
}
jobject gjobj = env->NewGlobalRef(jobj);
ALOGV("-Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring env->NewGlobalRef return (%0x)", gjobj);
setNativeBigInteger_l(env, thiz, gjobj);
env->DeleteLocalRef(jobj);
//env->DeleteLocalRef(cls);
}
JNIEXPORT void JNICALL
Java_nz_ac_unitec_mathutils_BigInteger_native_1finalize
(JNIEnv *env, jobject thiz)
{
ALOGV("+native_finalize");
jobject obj = getNativeBigInteger_l(env, thiz);
ALOGV("-Java_nz_ac_unitec_mathutils_BigInteger_native_1finalize getNativeBigInteger_l return (%0x)",
obj);
if (obj == NULL) {
ALOGE("-native_finalize getNativeBigInteger_l NULL");
return;
}
env->DeleteGlobalRef(obj);
setNativeBigInteger_l(env, thiz, NULL);
ALOGV("-native_finalize");
}
static JNINativeMethod gMethods[] = {
{"native_init", "()V",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_native_1init},
{"native_setup", "()V",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_native_1setup},
{"native_setup_bystring", "(Ljava/lang/String;I)V",
(void*)Java_nz_ac_unitec_mathutils_BigInteger_native_1setup_1bystring},
{"native_finalize", "()V",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_native_1finalize},
{"add", "(Lnz/ac/unitec/mathutils/BigInteger;)Lnz/ac/unitec/mathutils/BigInteger;",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_add},
{"multiply","(Lnz/ac/unitec/mathutils/BigInteger;)Lnz/ac/unitec/mathutils/BigInteger;",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_multiply},
{"subtract","(Lnz/ac/unitec/mathutils/BigInteger;)Lnz/ac/unitec/mathutils/BigInteger;",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_subtract},
{"toString","(I)Ljava/lang/String;",
(void *)Java_nz_ac_unitec_mathutils_BigInteger_toString}
};
int register_Java_nz_ac_unitec_mathutils_BigInteger(JNIEnv *env)
{
return jniRegisterNativeMethods(env, gClassBigInteger, gMethods, NELEM(gMethods));
}
回答：
您的代码失败，因为您对尚未释放回内存池中的对象的全局引用过多。全局引用表的最大大小可帮助您捕获内存泄漏并防止程序内存不足。您粘贴的日志消息告诉您这些对象是什么：java.math.BigInteger。
如果查看您的实现，native_setup_bystring可以看到您正在创建对新BigInteger对象的全局引用：
jobject gjobj = env->NewGlobalRef(jobs);全局引用不会自动垃圾收集[1]
[2]，因此您需要显式删除它们，这是在测试中找到的。
方法的问题在于，您正在使用对堆（您的long mNativeContext字段）中的直接内存引用来存储对内部对象的引用
。这种方法不是一个好方法，因为您要阻止JVM管理BigIntegers的垃圾回收。更好的方法是完全避免使用全局引用，而存储对象引用而不是long。如果执行此操作，则JVM将能够自动收集要分配的所有对象。
以上是 为什么需要释放在JNI本机函数中创建的全局引用？ 的全部内容， 来源链接： utcz.com/qa/413904.html
