> The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.
Double-ended queue (deque) is a sequence container implemented based on the queue data structure that follows the principles of First In First Out (FIFO) and Last In First Out (LIFO). It allows insertion and removal of elements at both the ends. **Deque** can dynamically adjust the capacity based on project requirements. It doubles the capacity each time. **Deque** differs from **[Queue](js-apis-queue.md)** and **[Vector](js-apis-vector.md)** mainly in the following aspects:
The **bundle.launcherBundleManager** module providers APIs for the **Home Screen** application to obtain the launcher ability information and shortcut information.
The **Screenshot** module provides APIs for you to set information such as the region to capture and the size of the screen region when capturing a screen.
> - The APIs of this module are no longer maintained since API version 7. You are advised to use [`@ohos.i18n`](js-apis-i18n.md) and [`@ohos.intl`](js-apis-intl.md) instead.
> - The APIs of this module are no longer maintained since API version 6. You are advised to use [`@ohos.net.http`](js-apis-http.md) instead.
>
>
> - The initial APIs of this module are supported since API version 3. Newly added APIs will be marked with a superscript to indicate their earliest API version.
The task pool provides a multi-thread running environment for applications. It helps reduce resource consumption and improve system performance. It also frees you from caring about the lifecycle of thread instances. You can use the **TaskPool** APIs to create background tasks and perform operations on them, for example, executing or canceling a task. Theoretically, you can create an unlimited number of tasks, but this is not recommended for memory considerations. In addition, you are not advised performing blocking operations in a task, especially indefinite blocking. Long-time blocking operations occupy worker threads and may block other task scheduling, adversely affecting your application performance.
You can determine the execution sequence of tasks with the same priority. They are executed in the same sequence as you call the task execution APIs. The default task priority is **MEDIUM**. (The task priority mechanism is not supported yet.)
If the number of tasks to be executed is greater than the number of worker threads in the task pool, the task pool scales out based on load balancing to minimize the waiting duration. Similarly, when the number of tasks to be executed falls below the number of worker threads, the task pool scales in to reduce the number of worker threads. (The load balancing mechanism is not supported yet.)
The **TaskPool** APIs return error codes in numeric format. For details about the error codes, see [Utils Error Codes](../errorcodes/errorcode-utils.md).
> **NOTE**<br>
> The initial APIs of this module are supported since API version 9. Newly added APIs will be marked with a superscript to indicate their earliest API version.
## Modules to Import
```js
importtaskpoolfrom'@ohos.taskpool';
```
## Priority
Enumerates the priorities available for created tasks. (This enum is not supported yet.)
| func | Function | Yes | Function to be passed in for task execution. For details about the supported return value types of the function, see [Sequenceable Data Types](#sequenceable-data-types). |
| args | unknown[] | No | Arguments of the function. For details about the supported parameter types, see [Sequenceable Data Types](#sequenceable-data-types).|
**Error codes**
For details about the error codes, see [Utils Error Codes](../errorcodes/errorcode-utils.md).
| function | Function | Yes | Yes | Function to be passed in during task creation. For details about the supported return value types of the function, see [Sequenceable Data Types](#sequenceable-data-types). |
| arguments | unknown[] | Yes | Yes | Arguments of the function. For details about the supported parameter types, see [Sequenceable Data Types](#sequenceable-data-types).|
Executes a task in the task pool. You must pass in a function and arguments to execute the task, and the task executed in this mode cannot be canceled.
| func | Function | Yes | Function used to execute the task. For details about the supported return value types of the function, see [Sequenceable Data Types](#sequenceable-data-types). |
| args | unknown[] | No | Arguments of the function. For details about the supported parameter types, see [Sequenceable Data Types](#sequenceable-data-types).|
For details about the error codes, see [Utils Error Codes](../errorcodes/errorcode-utils.md).
| ID| Error Message |
| -------- | ------------------------- |
| 10200015 | If the task is not exist. |
| 10200016 | If the task is running. |
**Example**
```js
functionfunc(args){
"use concurrent"
console.log("func: "+args);
returnargs;
}
lettask=newtaskpool.Task(func,"this is first Task");
letvalue=taskpool.execute(task);
taskpool.cancel(task);
```
## Additional Information
### Sequenceable Data Types
The following sequenceable data types are supported: All Primitive Type (excluding symbol), Date, String, RegExp, Array, Map, Set, Object, ArrayBuffer, and TypedArray.
### Precautions
A task in the task pool can reference only variables passed in by input parameters or imported variables. It does not support closure variables.
```js
// 1. Reference a variable passed in by the input parameter.
functionfunc(args){
"use concurrent"
console.log("func: "+args);
returnargs;
}
lettask=newtaskpool.Task(func,"create task, then execute");
letval1=taskpool.execute(task);
letval2=taskpool.execute(func,"execute task by func");
```
```js
// 2. Reference an imported variable.
// b.ts
exportvarc=2000;
// a.ts
import{c}from'./b'
functiontest(a){
"use concurrent"
console.log(a);
console.log(c);
returna;
}
lettask=newtaskpool.Task(test,"create task, then execute");
letval1=taskpool.execute(task);
letval2=taskpool.execute(test,"execute task by func");
The **WantAgent** module provides APIs for creating and comparing **WantAgent** objects, and obtaining the user ID and bundle name of a **WantAgent** object.
The **Window** module provides basic window management capabilities, such as creating and destroying the current window, setting properties for the current window, and managing and scheduling windows.
