JNI，如何在JNI中访问当前Java线程

Question

有没有办法从JNI获取Java线程(ID，名称)。我不是在谈论将Thread.currentThread().getId()从java传递给JNI。JNI是否提供API来访问当前正在运行的线程？

Answer 1

你可以(正如亚历克斯提到的那样)求助于java.lang.Thread。

// First, we have to find Thread class
jclass cls = (*env)->FindClass(env, "java/lang/Thread");

// Then, we can look for it's static method 'currentThread'
/* Remember that you can always get method signature using javap tool
     > javap -s -p java.lang.Thread | grep -A 1 currentThread
         public static native java.lang.Thread currentThread();
           descriptor: ()Ljava/lang/Thread;
*/
jmethodID mid =
  (*env)->GetStaticMethodID(env, cls, "currentThread", "()Ljava/lang/Thread;");

// Once you have method, you can call it. Remember that result is
// a jobject
jobject thread = (*env)->CallStaticObjectMethod(env, cls, mid);
if( thread == NULL ) {
  printf("Error while calling static method: currentThread\n");
}

// Now, we have to find another method - 'getId'
/* Remember that you can always get method signature using javap tool
     > javap -s -p java.lang.Thread | grep -A 1 getId
         public long getId();
           descriptor: ()Jjavap -s -p java.lang.Thread | grep -A 1 currentThread
*/
jmethodID mid_getid =
  (*env)->GetMethodID(env, cls, "getId", "()J");
if( mid_getid == NULL ) {
  printf("Error while calling GetMethodID for: getId\n");
}

// This time, we are calling instance method, note the difference
// in Call... method
jlong tid = (*env)->CallLongMethod(env, thread, mid_getid);

// Finally, let's call 'getName' of Thread object
/* Remember that you can always get method signature using javap tool
     > javap -s -p java.lang.Thread | grep -A 1 getName
         public final java.lang.String getName();
           descriptor: ()Ljava/lang/String;
*/
jmethodID mid_getname =
  (*env)->GetMethodID(env, cls, "getName", "()Ljava/lang/String;");

if( mid_getname == NULL ) {
  printf("Error while calling GetMethodID for: getName\n");
}

// As above, we are calling instance method
jobject tname = (*env)->CallObjectMethod(env, thread, mid_getname);

// Remember to retrieve characters from String object
const char *c_str;
c_str = (*env)->GetStringUTFChars(env, tname, NULL);
if(c_str == NULL) {
  return;
}

// display message from JNI
printf("[C   ] name: %s id: %ld\n", c_str, tid);

// and make sure to release allocated memory before leaving JNI
(*env)->ReleaseStringUTFChars(env, tname, c_str);

你可以在这里找到完整的样本：https://github.com/mkowsiak/jnicookbook/tree/master/recipes/recipeNo044