# groonga - An open-source fulltext search engine and column store.

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# 7.3.50. `request_cancel`

## 7.3.50.1. Summary

New in version 4.0.9.

`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 executable file based server but can’t use with groonga-httpd.)

See Request ID about request ID.

If the request is canceled, a Return code of the canceled request as below.

> - `-5` (`GRN_INTERRUPTED_FUNCTION_CALL`) (Groonga version 6.0.1 before)
> - `-77` (`GRN_CANCEL`) (Groonga version 6.0.1 or later)

## 7.3.50.2. Syntax

This command takes only one required parameter:

    request_cancel id

## 7.3.50.3. Usage

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` in return value:

    $ 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 Return code:

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

## 7.3.50.4. Parameters

This section describes parameters of `request_cancel`.

### 7.3.50.4.1. Required parameters

There is required parameter, `id`.

#### 7.3.50.4.1.1. `id`

Specifies the ID for the target request.

## 7.3.50.5. Return value

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

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

`HEADER`

> See Output format about `HEADER`.

`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`.

## 7.3.50.6. See also

- Request ID