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async_context.md
[add] server:lib:node_modules
Christian Fraß
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at 2021-03-08 23:52:07
async_context.md
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# AsyncContext The [Napi::AsyncWorker](async_worker.md) class may not be appropriate for every scenario. When using any other async mechanism, introducing a new class `Napi::AsyncContext` is necessary to ensure an async operation is properly tracked by the runtime. The `Napi::AsyncContext` class can be passed to [Napi::Function::MakeCallback()](function.md) method to properly restore the correct async execution context. ## Methods ### Constructor Creates a new `Napi::AsyncContext`. ```cpp explicit Napi::AsyncContext::AsyncContext(napi_env env, const char* resource_name); ``` - `[in] env`: The environment in which to create the `Napi::AsyncContext`. - `[in] resource_name`: Null-terminated strings that represents the identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API. ### Constructor Creates a new `Napi::AsyncContext`. ```cpp explicit Napi::AsyncContext::AsyncContext(napi_env env, const char* resource_name, const Napi::Object& resource); ``` - `[in] env`: The environment in which to create the `Napi::AsyncContext`. - `[in] resource_name`: Null-terminated strings that represents the identifier for the kind of resource that is being provided for diagnostic information exposed by the `async_hooks` API. - `[in] resource`: Object associated with the asynchronous operation that will be passed to possible `async_hooks`. ### Destructor The `Napi::AsyncContext` to be destroyed. ```cpp virtual Napi::AsyncContext::~AsyncContext(); ``` ### Env Requests the environment in which the async context has been initially created. ```cpp Napi::Env Env() const; ``` Returns the `Napi::Env` environment in which the async context has been created. ## Operator ```cpp Napi::AsyncContext::operator napi_async_context() const; ``` Returns the N-API `napi_async_context` wrapped by the `Napi::AsyncContext` object. This can be used to mix usage of the C N-API and node-addon-api. ## Example ```cpp #include "napi.h" void MakeCallbackWithAsyncContext(const Napi::CallbackInfo& info) { Napi::Function callback = info[0].As<Napi::Function>(); Napi::Object resource = info[1].As<Napi::Object>(); // Create a new async context instance. Napi::AsyncContext context(info.Env(), "async_context_test", resource); // Invoke the callback with the async context instance. callback.MakeCallback(Napi::Object::New(info.Env()), std::initializer_list<napi_value>{}, context); // The async context instance is automatically destroyed here because it's // block-scope like `Napi::HandleScope`. } ```