multiwait

multiwait allows to run a command after conditions have been fulfilled. For example you can use it to start a program after Redis has finished loading its dataset into memory, or after a lock file has disappeared.

The settings are given in a YAML file, for example:

defaults:
    timeout: 60

conditions:
    - redis-dataset-loaded
    - file-absent:
        path: /path/to/lockfile
        warmup: 10
        test_interval: 1
    - file-present:
        path: /path/to/socket
        timeout: 15

Then you point the multiwait command to the settings and the command you want to run:

$ multiwait --settings /path/to/settings.yaml echo foo

Here echo foo will only be run once Redis has finished loading its dataset in memory, the /path/to/lockfile has disappeared, and /path/to/socket exists.

You can also specify simple conditions directly from the command line:

$ multiwait --cond file-absent:path=/path/to/lockfile,timeout=3 echo foo

The command will replace the multiwait process, keeping the same PID, so it's safe for use in process managers.

If no command is specified, check all conditions and exit with a non-zero return code if one of them fails.

Conditions

The conditions to fulfill before running the commands are described in the conditions key of the settings file. It must be a list containing conditions definitions. Each entry must contain an object with the condition name as the single key, and arguments to the definition. As a shortcut you can also write the condition name alone if doesn't take arguments or you just want to use the defaults; in the example above redis-dataset-loaded is a shortcut for redis-dataset-loaded: {}.

All conditions at least accept the following arguments:

timeout

Maximum execution time for the condition, in seconds before giving up. The default is no timeout.

warmup

Sleep for this amount of time before starting testing for the condition. The default is no warm-up time.

test_interval

An interval in seconds between two tests. The default is 0.1 second.

Global default arguments can be specified in the defaults top-level key in the settings file. They are overridden by the conditions-specific; in the example above all conditions have a 60 seconds timeout, except file-present which has a 15 seconds timeout.

Built-in conditions

redis-dataset-loaded

Wait until Redis has finished loading its dataset in memory. Requires the redis package.

• host: the host of the Redis server (default: "localhost")
• port: the port number of the Redis server (default: 6379)
• password: the password used to connect to the Redis server (default: no password)
• ignore_connection_errors: ignore connection errors (default: True)

file-present

Wait until a file is present on the filesystem.

• path (required): the path of the file

file-absent

Wait until a file is not present on the filesystem.

• path (required): the path of the file

x11-running

Wait until the X11 system is running.

• default_display: for systems not using Xauthority cookies, try to connect to this display (default: ":0")