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1# JSVM-API常见问题
2<!--Kit: NDK Development-->
3<!--Subsystem: arkcompiler-->
4<!--Owner: @yuanxiaogou; @string_sz-->
5<!--Designer: @knightaoko-->
6<!--Tester: @test_lzz-->
7<!--Adviser: @fang-jinxu-->
8
9## 定位方法
10
11程序崩溃类问题：通过C++崩溃时调用栈查询FAQ的方式定位代码问题
12
13程序执行结果不符合预期类问题：需应用通过JSVM-API调用返回值定位到执行失败或执行结果不符合预期的位置，通过函数名查询FAQ
14
15## 程序崩溃类
16
171. Q：在`OH_JSVM_RunScript`或`OH_JSVM_CallFunction`时crash，调用栈顶层为`SetReturnValue`
18
19   ```
20   #00 pc 0000000000c68ef0 /system/lib64/ndk/libjsvm.so(v8impl::(anonymous namespace)::FunctionCallbackWrapper::SetReturnValue(JSVM_Value__*)+16)
21   #01 pc 0000000000c5ad30 /system/lib64/ndk/libjsvm.so(v8impl::(anonymous namespace)::FunctionCallbackWrapper::Invoke(v8::FunctionCallbackInfo<v8::Value> const&)+332)
22   #02 pc 00000000014a9e58 /system/lib64/ndk/libjsvm.so
23   #03 pc 00000000014a95d4 /system/lib64/ndk/libjsvm.so(v8::internal::Builtin_HandleApiCall(int, unsigned long*, v8::internal::Isolate*)+176)
24   #04 pc 0000000000f7dab4 /system/lib64/ndk/libjsvm.so(Builtins_CEntry_Return1_ArgvOnStack_BuiltinExit+84)
25   #05 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
26   #06 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
27   #07 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
28   #08 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
29   #09 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
30   #10 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
31   #11 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
32   #12 pc 0000000000eece40 /system/lib64/ndk/libjsvm.so(Builtins_InterpreterEntryTrampoline+288)
33   #13 pc 0000000000fe09f4 /system/lib64/ndk/libjsvm.so(Builtins_PromiseFulfillReactionJob+52)
34   #14 pc 0000000000f155c0 /system/lib64/ndk/libjsvm.so(Builtins_RunMicrotasks+672)
35   #15 pc 0000000000eeab54 /system/lib64/ndk/libjsvm.so(Builtins_JSRunMicrotasksEntry+148)
36   #16 pc 00000000015bed78 /system/lib64/ndk/libjsvm.so(v8::internal::(anonymous namespace)::Invoke(v8::internal::Isolate*, v8::internal::(anonymous namespace)::InvokeParams const&)+2520)
37   #17 pc 00000000015bf50c /system/lib64/ndk/libjsvm.so(v8::internal::(anonymous namespace)::InvokeWithTryCatch(v8::internal::Isolate*, v8::internal::(anonymous namespace)::InvokeParams const&)+104)
38   #18 pc 00000000015bf730 /system/lib64/ndk/libjsvm.so(v8::internal::Execution::TryRunMicrotasks(v8::internal::Isolate*, v8::internal::MicrotaskQueue*)+80)
39   #19 pc 00000000015ecf4c /system/lib64/ndk/libjsvm.so(v8::internal::MicrotaskQueue::RunMicrotasks(v8::internal::Isolate*)+312)
40   #20 pc 00000000015ecd9c /system/lib64/ndk/libjsvm.so(v8::internal::MicrotaskQueue::PerformCheckpointInternal(v8::Isolate*)+52)
41   #21 pc 00000000015deaa0 /system/lib64/ndk/libjsvm.so(v8::internal::Isolate::FireCallCompletedCallbackInternal(v8::internal::MicrotaskQueue*)+280)
42   #22 pc 00000000014334e8 /system/lib64/ndk/libjsvm.so(v8::CallDepthScope<true>::~CallDepthScope()+248)
43   #23 pc 00000000014330a4 /system/lib64/ndk/libjsvm.so(v8::Script::Run(v8::Local<v8::Context>, v8::Local<v8::Data>)+884)
44   #24 pc 0000000000c5c2ac /system/lib64/ndk/libjsvm.so(OH_JSVM_RunScript+272)
45   ```
46
47   A：`SetReturnValue`用于设置js函数的返回值，在js完成注入的native函数调用后触发。需检查native函数的返回值是否正确，如返回值（`JSVM_Value`）是否未初始化就直接返回。
48
492. Q：js执行虚拟机初始化注入的native函数时程序崩溃
50
51   A：检查`JSVM_CallbackStruct`是否为栈上变量。如果跨函数使用，需确保`JSVM_CallbackStruct`的生命周期长于`JSVM_Env`的生命周期。
52
53   ```
54   func {
55   	// ...
56       JSVM_CallbackStruct param[] = {
57           {.data = nullptr, .callback = ConsoleInfo},
58           {.data = nullptr, .callback = Add},
59       };
60       JSVM_PropertyDescriptor descriptor[] = {
61           {"consoleinfo", NULL, &param[0], NULL, NULL, NULL, JSVM_DEFAULT},
62           {"add", NULL, &param[1], NULL, NULL, NULL, JSVM_DEFAULT},
63       };
64       // create env, register native method, and open env scope
65       JSVM_Env env;
66       OH_JSVM_CreateEnv(vm, sizeof(descriptor) / sizeof(descriptor[0]), descriptor, &env);
67      // ...
68       OH_JSVM_DestroyEnv(env);
69      // ...
70   }
71   ```
72
73   在上述示例代码中，JS引擎实例在函数结束前被关闭，因此可以直接使用栈上的`param`。
74
753. Q：`OH_JSVM_ReferenceRef`、`OH_JSVM_ReferenceUnRef`、`OH_JSVM_CreateReference`、`OH_JSVM_DeleteReference`时程序崩溃
76
77   A：检查是否同时有多个线程持有和释放`JSVM_Ref`，见 [多线程共享引擎实例](jsvm-guidelines.md#多线程共享引擎实例)
78
794. Q：在虚拟机引擎实例中创建JS类型实例崩溃（如`OH_JSVM_CreateDouble`），调用栈如下
80
81   ```
82   #00 pc 0000000001d209e4/system/lib64/ndk/libjsvm.so(v8::base::0S::Abort()+28)
83   #01 pc 0000000001408480/system/lib64/ndk/libjsvm.so(v8::Utils::ReportApiFailure(char const*,char const*)+124)
84   #02 pc 00000000015c99b8/system/lib64/ndk/libjsvm.so(v8::internal::HandleScope::Extend(v8::internal::Isolate*+200)
85   ```
86
87   A：检查HandleScope的使用是否正确，参考[生命周期管理](jsvm-guidelines.md#生命周期管理)
88
89## JSVM-API执行失败类
90
911. Q：`OH_JSVM_GetCbInfo`无法获取JS函数参数
92
93   A：检查函数传递的参数是否正确，见[获取JS传入参数及其数量](jsvm-guidelines.md#获取js传入参数及其数量)
94
952. Q：`OH_JSVM_CreateFunction`等函数调用失败，返回值为`JSVM_PENDING_EXCEPTION`
96
97   A：`JSVM_PENDING_EXCEPTION`表明当前虚拟机环境中存在未处理的异常，可能是由于本次调用产生的`JS`异常，也可能是之前调用产生的未被清理的异常。可以通过在函数调用前插入`OH_JSVM_GetAndClearLastException`排查之前是否有未清除的异常。如果为之前的未清理异常，检查是否有JSVM接口调用未处理异常返回值；如果是本次产生的异常，需清理异常，避免影响后续的函数调用。获取并清理异常的函数为`OH_JSVM_GetAndClearLastException`
98
993. Q：JS执行时无法找到 `OH_JSVM_DefineClass` 定义的类
100
101   A：检查是否将定义的类绑定到上下文中，见[上下文绑定对象](jsvm-guidelines.md#上下文绑定对象)
102