# groonga - オープンソースのカラムストア機能付き全文検索エンジン

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# 7.3.26. `request_cancel`

## 7.3.26.1. 概要

注釈

`request_cancel` command is an experimental feature.

バージョン 4.0.9 で追加.

`request_cancel` command cancels a running request.

There are some limitations:

> - Request ID must be managed by user. (You need to assign unique key for each request.)
> - Cancel request may be ignored. (You can send `request_cancel` command multiple times for the same request ID.)
> - Only multithreading type Groonga server is supported. (You can use with groongaコマンド based server but can't use with groonga-httpd.)

See Request ID about request ID.

If request is canceled, the canceled request has `-5` (`GRN_INTERRUPTED_FUNCTION_CALL`) as リターンコード.

## 7.3.26.2. 構文

`request_cancel` command takes only one parameter.

The required parameter is only `id`:

    request_cancel id

## 7.3.26.3. 使い方

Here is an example of `request_cancel` command:

    $ curl 'http://localhost:10041/d/select?table=LargeTable&filter=true&request_id=unique-id-1' &
    # The above "select" takes a long time...
    # Point: "request_id=unique-id-1"
    $ curl 'http://localhost:10041/d/request_cancel?id=unique-id-1'
    [[...], {"id": "unique-id-1", "canceled": true}]
    # Point: "id=unique-id-1"

Assume that the first `select` command takes a long time. `unique-id-1` request ID is assigned to the `select` command by `request_id=unique-id-1` parameter.

The second `request_cancel` command passes `id=unique-id-1` parameter. `unique-id-1` is the same request ID passed in `select` command.

The `select` command may not be canceled immediately. And the cancel request may be ignored.

You can send cancel request for the same request ID multiple times. If the target request is canceled or finished, `"canceled"` value is changed to `false` from `true`:

    $ curl 'http://localhost:10041/d/request_cancel?id=unique-id-1'
    [[...], {"id": "unique-id-1", "canceled": true}]
    # "select" is still running... ("canceled" is "true")
    $ curl 'http://localhost:10041/d/request_cancel?id=unique-id-1'
    [[...], {"id": "unique-id-1", "canceled": true}]
    # "select" is still running... ("canceled" is "true")
    $ curl 'http://localhost:10041/d/request_cancel?id=unique-id-1'
    [[...], {"id": "unique-id-1", "canceled": false}]
    # "select" is canceled or finished. ("canceled" is "false")

If the `select` command is canceled, response of the `select` command has `-5` (`GRN_INTERRUPTED_FUNCTION_CALL`) as リターンコード:

    $ curl 'http://localhost:10041/d/select?table=LargeTable&filter=true&request_id=unique-id-1' &
    [[-5, ...], ...]

## 7.3.26.4. 引数

This section describes parameters of `request_cancel`.

### 7.3.26.4.1. 必須引数

There is required parameter, `id`.

#### 7.3.26.4.1.1. `id`

It specifies the ID for the target request.

## 7.3.26.5. 戻り値

`request_cancel` command returns the result of the cancel request:

    [
      HEADER,
      {
        "id":       ID,
        "canceled": CANCEL_REQUEST_IS_ACCEPTED_OR_NOT
      }
    ]

`HEADER`

> `HEADER` については 出力形式 を参照してください。

`ID`

> The ID of the target request.

`CANCEL_REQUEST_IS_ACCEPTED_OR_NOT`

> If the cancel request is accepted, this is `true`, otherwise this is `false`.

> Note that "cancel request is accepted" doesn't means that "the target request is canceled". It just means "cancel request is notified to the target request but the cancel request may be ignored by the target request".

> If request assigned with the request ID doesn't exist, this is `false`.

## 7.3.26.6. 参考

- Request ID

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