# 使用JSVM-API接口进行任务队列相关开发 ## 简介 在虚拟机内启动任务队列，检查队列中是否有待处理的微任务。任务队列可由外部事件循环执行。 ## 基本概念 * **任务队列**：用于管理异步任务的调度和执行，确保任务按顺序处理。 * **微任务**：微任务是一种任务调度机制，主要用于处理那些需要尽快执行的较小任务，它们通常具有较高的优先级。 ## 接口说明 |接口|功能说明| |:---------------------------------|:----------| |OH_JSVM_PumpMessageLoop|启动任务队列的运行| |OH_JSVM_PerformMicrotaskCheckpoint|执行任务队列里的微任务| |OH_JSVM_SetMicrotaskPolicy|设置微任务执行策略| ## 使用示例 JSVM-API接口开发流程参考[使用JSVM-API实现JS与C/C++语言交互开发流程](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/use-jsvm-process)，本文仅展示接口对应的C++相关代码。 权限要求：Wasm字节码需要应用拥有JIT权限才能执行，可参考[JSVM 申请JIT权限指导](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/jsvm-apply-jit-profile)申请对应权限。 运行限制：当前 JSVM 版本在坚盾守护模式下将禁用 WebAssembly 全部功能模块。开发者需针对此限制进行应用兼容性评估，具体技术规范详见[JSVM 坚盾守护模式](https://developer.huawei.com/consumer/cn/doc/harmonyos-guides/jsvm-secure-shield-mode)。 ### OH_JSVM_PumpMessageLoop & OH_JSVM_PerformMicrotaskCheckpoint 启动任务队列，执行任务。 cpp部分代码： #include #include // ... // 待执行的js代码 static const char *STR_TASK = R"JS( // wasm 字节码 (以add 模块为例) // 以下 wasmBuffer 对应的 wasm 字节码文本格式如下所示，只包含了一个函数 add // (module // (func $add (param $lhs i32) (param $rhs i32) (result i32) // local.get $lhs // local.get $rhs // i32.add // ) // (export "add" (func $add)) // ) var wasmBytes = new Uint8Array([0x00, 0x61, 0x73, 0x6d, 0x01, 0x00, 0x00, 0x00, 0x01, 0x07, 0x01, 0x60, 0x02, 0x7f, 0x7f, 0x01, 0x7f, 0x03, 0x02, 0x01, 0x00, 0x07, 0x07, 0x01, 0x03, 0x61, 0x64, 0x64, 0x00, 0x00, 0x0a, 0x09, 0x01, 0x07, 0x00, 0x20, 0x00, 0x20, 0x01, 0x6a, 0x0b]); var p = WebAssembly.instantiate(wasmBytes, {}); p.then((result) => { consoleinfo("Called with instance " + result); }); p.finally(() => { consoleinfo("Called Finally"); }); )JS"; // 保证js代码中的打印信息可以正常输出 static JSVM_Value ConsoleInfo(JSVM_Env env, JSVM_CallbackInfo info) { size_t argc = 1; JSVM_Value args[1]; #define MAX_LOG_LENGTH 255 char log[MAX_LOG_LENGTH + 1] = ""; size_t logLength = 0; JSVM_CALL(OH_JSVM_GetCbInfo(env, info, &argc, args, NULL, NULL)); OH_JSVM_GetValueStringUtf8(env, args[0], log, MAX_LOG_LENGTH, &logLength); log[MAX_LOG_LENGTH] = 0; OH_LOG_INFO(LOG_APP, "JSVM API TEST: %{public}s", log); return nullptr; } // 注册consoleinfo的方法 JSVM_CallbackStruct param[] = { {.data = nullptr, .callback = ConsoleInfo}, }; JSVM_PropertyDescriptor descriptor[] = { {"consoleinfo", NULL, ¶m[0], NULL, NULL, NULL, JSVM_DEFAULT}, }; static int32_t TestJSVM() { JSVM_InitOptions init_options; memset(&init_options, 0, sizeof(init_options)); if (g_aa == 0) { OH_JSVM_Init(&init_options); g_aa++; } // 创建JavaScript虚拟机实例,打开虚拟机作用域 JSVM_VM vm; JSVM_CreateVMOptions options; memset(&options, 0, sizeof(options)); CHECK(OH_JSVM_CreateVM(&options, &vm)); JSVM_VMScope vm_scope; CHECK(OH_JSVM_OpenVMScope(vm, &vm_scope)); JSVM_Env env; CHECK(OH_JSVM_CreateEnv(vm, sizeof(descriptor) / sizeof(descriptor[0]), descriptor, &env)); JSVM_EnvScope envScope; CHECK_RET(OH_JSVM_OpenEnvScope(env, &envScope)); JSVM_HandleScope handlescope; CHECK_RET(OH_JSVM_OpenHandleScope(env, &handlescope)); JSVM_Value sourcecodevalue; CHECK_RET(OH_JSVM_CreateStringUtf8(env, STR_TASK, strlen(STR_TASK), &sourcecodevalue)); JSVM_Script script; CHECK_RET(OH_JSVM_CompileScript(env, sourcecodevalue, nullptr, 0, true, nullptr, &script)); JSVM_Value result; CHECK_RET(OH_JSVM_RunScript(env, script, &result)); bool rst = false; auto start = std::chrono::system_clock::now(); while (true) { // 如果任务队列中没有任务启动，则rst设置为false CHECK_RET(OH_JSVM_PumpMessageLoop(vm, &rst)); CHECK_RET(OH_JSVM_PerformMicrotaskCheckpoint(vm)); // 定时退出 auto now = std::chrono::system_clock::now(); auto cost = std::chrono::duration_cast(now - start).count(); const int timeoutMs = 100; if (cost > timeoutMs) { break; } } // 关闭并销毁环境和虚拟机 CHECK_RET(OH_JSVM_CloseHandleScope(env, handlescope)); CHECK_RET(OH_JSVM_CloseEnvScope(env, envScope)); CHECK(OH_JSVM_DestroyEnv(env)); CHECK(OH_JSVM_CloseVMScope(vm, vm_scope)); CHECK(OH_JSVM_DestroyVM(vm)); return 0; } 预期输出结果： ```txt JSVM API TEST: Called with instance [object Object] JSVM API TEST: Called Finally ``` ### OH_JSVM_SetMicrotaskPolicy 修改微任务执行策略，通过该接口，用户可以将策略设置为 JSVM_MicrotaskPolicy::JSVM_MICROTASK_EXPLICIT 或 JSVM_MicrotaskPolicy::JSVM_MICROTASK_AUTO。默认模式下，微任务的执行策略为 JSVM_MicrotaskPolicy::JSVM_MICROTASK_AUTO。 微任务策略： * JSVM_MicrotaskPolicy::JSVM_MICROTASK_EXPLICIT ： 微任务在用户调用 OH_JSVM_PerformMicrotaskCheckpoint 后执行 * JSVM_MicrotaskPolicy::JSVM_MICROTASK_AUTO： 微任务在 JS 调用栈为空时自动执行 cpp 部分代码 ```cpp // OH_JSVM_SetMicrotaskPolicy的样例方法 static int SetMicrotaskPolicy(JSVM_VM vm, JSVM_Env env) { // 默认或将策略设置为 JSVM_MICROTASK_AUTO 的行为 const char *scriptEvalMicrotask = R"JS( evaluateMicrotask = false; Promise.resolve().then(()=>{ evaluateMicrotask = true; }); )JS"; JSVM_Script script; JSVM_Value jsSrc; JSVM_Value result; CHECK_RET(OH_JSVM_CreateStringUtf8(env, scriptEvalMicrotask, JSVM_AUTO_LENGTH, &jsSrc)); CHECK_RET(OH_JSVM_CompileScript(env, jsSrc, nullptr, 0, true, nullptr, &script)); CHECK_RET(OH_JSVM_RunScript(env, script, &result)); JSVM_Value global; CHECK_RET(OH_JSVM_GetGlobal(env, &global)); JSVM_Value hasEvaluateMicrotask; CHECK_RET(OH_JSVM_GetNamedProperty(env, global, "evaluateMicrotask", &hasEvaluateMicrotask)); bool val = false; CHECK_RET(OH_JSVM_GetValueBool(env, hasEvaluateMicrotask, &val)); OH_LOG_INFO(LOG_APP, "Policy :JSVM_MICROTASK_AUTO, evaluateMicrotask : %{public}d", val); // 策略设置为 JSVM_MICROTASK_EXPLICIT 的行为 CHECK_RET(OH_JSVM_SetMicrotaskPolicy(vm, JSVM_MicrotaskPolicy::JSVM_MICROTASK_EXPLICIT)); CHECK_RET(OH_JSVM_RunScript(env, script, &result)); CHECK_RET(OH_JSVM_GetNamedProperty(env, global, "evaluateMicrotask", &hasEvaluateMicrotask)); CHECK_RET(OH_JSVM_GetValueBool(env, hasEvaluateMicrotask, &val)); OH_LOG_INFO( LOG_APP, "Policy: JSVM_MICROTASK_AUTO, evaluateMicrotask before calling OH_JSVM_PerformMicrotaskCheckpoint: %{public}d", val); CHECK_RET(OH_JSVM_PerformMicrotaskCheckpoint(vm)); CHECK_RET(OH_JSVM_GetNamedProperty(env, global, "evaluateMicrotask", &hasEvaluateMicrotask)); CHECK_RET(OH_JSVM_GetValueBool(env, hasEvaluateMicrotask, &val)); OH_LOG_INFO( LOG_APP, "Policy: JSVM_MICROTASK_AUTO, evaluateMicrotask after calling OH_JSVM_PerformMicrotaskCheckpoint: %{public}d", val); return 0; } static void RunDemo(JSVM_VM vm, JSVM_Env env) { if (SetMicrotaskPolicy(vm, env) != 0) { OH_LOG_INFO(LOG_APP, "Run Microtask Policy failed"); } } static int32_t TestJSVM() { JSVM_InitOptions initOptions = {0}; JSVM_VM vm; JSVM_Env env = nullptr; JSVM_VMScope vmScope; JSVM_EnvScope envScope; JSVM_HandleScope handleScope; JSVM_Value result; // 初始化JavaScript引擎实例 if (g_aa == 0) { g_aa++; CHECK(OH_JSVM_Init(&initOptions)); } // 创建JSVM环境 CHECK(OH_JSVM_CreateVM(nullptr, &vm)); CHECK(OH_JSVM_OpenVMScope(vm, &vmScope)); CHECK(OH_JSVM_CreateEnv(vm, 0, nullptr, &env)); CHECK_RET(OH_JSVM_OpenEnvScope(env, &envScope)); CHECK_RET(OH_JSVM_OpenHandleScope(env, &handleScope)); // 通过script调用测试函数 RunDemo(vm, env); // 销毁JSVM环境 CHECK_RET(OH_JSVM_CloseHandleScope(env, handleScope)); CHECK_RET(OH_JSVM_CloseEnvScope(env, envScope)); CHECK(OH_JSVM_DestroyEnv(env)); CHECK(OH_JSVM_CloseVMScope(vm, vmScope)); CHECK(OH_JSVM_DestroyVM(vm)); return 0; } ``` 预期输出结果： ```txt Policy :JSVM_MICROTASK_AUTO, evaluateMicrotask : 1 Policy :JSVM_MICROTASK_AUTO, evaluateMicrotask before calling OH_JSVM_PerformMicrotaskCheckpoint: 0 Policy :JSVM_MICROTASK_AUTO, evaluateMicrotask after calling OH_JSVM_PerformMicrotaskCheckpoint: 1 ```