JNI中异常报错底层处理逻辑

demo：

if(env->ExcetionCheck()) {
    env->ExcetionClear();
}

http://aospxref.com/android-10.0.0_r47/xref/art/runtime/jni/check_jni.cc#2020

  static jboolean ExceptionCheck(JNIEnv* env) {
    CHECK_ATTACHED_THREAD(__FUNCTION__, JNI_FALSE);
    ScopedObjectAccess soa(env);
    ScopedCheck sc(kFlag_CritOkay | kFlag_ExcepOkay, __FUNCTION__);
    JniValueType args[1] = {{.E = env}};
    if (sc.Check(soa, true, "E", args)) { // 会check下是否为异常
      JniValueType result;
      result.b = baseEnv(env)->ExceptionCheck(env); // 然后通过顶层的env来捕获这个有异常
      if (sc.Check(soa, false, "b", &result)) {
        return result.b;
      }
    }
    return JNI_FALSE;
  }

http://aospxref.com/android-10.0.0_r47/xref/art/runtime/jni/check_jni.cc#535

 /**
   * The format string is a sequence of the following characters,
   * and must be followed by arguments of the corresponding types
   * in the same order.
   *
   * Java primitive types:
   * B - jbyte
   * C - jchar
   * D - jdouble
   * F - jfloat
   * I - jint
   * J - jlong
   * S - jshort
   * Z - jboolean (shown as true and false)
   * V - void
   *
   * Java reference types:
   * L - jobject
   * a - jarray
   * c - jclass
   * s - jstring
   *
   * JNI types:
   * b - jboolean (shown as JNI_TRUE and JNI_FALSE)
   * f - jfieldID
   * m - jmethodID
   * p - void*
   * r - jint (for release mode arguments)
   * u - const char* (Modified UTF-8)
   * z - jsize (for lengths; use i if negative values are okay)
   * v - JavaVM*
   * E - JNIEnv*
   * . - VarArgs* for Jni calls with variable length arguments
   *
   * Use the kFlag_NullableUtf flag where 'u' field(s) are nullable.
   */
  bool Check(ScopedObjectAccess& soa, bool entry, const char* fmt, JniValueType* args)
      REQUIRES_SHARED(Locks::mutator_lock_) {
    ArtMethod* traceMethod = nullptr;
    if (has_method_ && soa.Vm()->IsTracingEnabled()) {
      // We need to guard some of the invocation interface's calls: a bad caller might
      // use DetachCurrentThread or GetEnv on a thread that's not yet attached.
      Thread* self = Thread::Current();
      if ((flags_ & kFlag_Invocation) == 0 || self != nullptr) {
        traceMethod = self->GetCurrentMethod(nullptr);
      }
    }

    if (((flags_ & kFlag_ForceTrace) != 0) ||
        (traceMethod != nullptr && soa.Vm()->ShouldTrace(traceMethod))) {
      std::string msg;
      for (size_t i = 0; fmt[i] != '\0'; ++i) {
        TracePossibleHeapValue(soa, entry, fmt[i], args[i], &msg);
        if (fmt[i + 1] != '\0') {
          StringAppendF(&msg, ", ");
        }
      }

      if ((flags_ & kFlag_ForceTrace) != 0) {
        LOG(INFO) << "JNI: call to " << function_name_ << "(" << msg << ")";
      } else if (entry) {
        if (has_method_) {
          std::string methodName(ArtMethod::PrettyMethod(traceMethod, false));
          LOG(INFO) << "JNI: " << methodName << " -> " << function_name_ << "(" << msg << ")";
          indent_ = methodName.size() + 1;
        } else {
          LOG(INFO) << "JNI: -> " << function_name_ << "(" << msg << ")";
          indent_ = 0;
        }
      } else {
        LOG(INFO) << StringPrintf("JNI: %*s<- %s returned %s", indent_, "", function_name_, msg.c_str());
      }
    }

    // We always do the thorough checks on entry, and never on exit...
    if (entry) {
      for (size_t i = 0; fmt[i] != '\0'; ++i) {
        if (!CheckPossibleHeapValue(soa, fmt[i], args[i])) {
          return false;
        }
      }
    }
    return true;
  }