Scheduler XML Reference | MuleSoft Documentation
# Scheduler XML Reference
A XML for the Scheduler has these elements:
  * `scheduler` parent element that encloses the rest of the elements.
  * `scheduling-strategy` block inside `scheduler`.
  * `fixed-frequency` or `cron` element inside the `scheduling-strategy` block.


## `<scheduler>` Properties
Attribute | Description | Example  
---|---|---  
`disallowConcurrentExecution` | Skips the next scheduled flow execution if the last one has not ended. Next attempt to execute will be after another frequency period. Default value is `false`. | `disallowConcurrentExecution="true"`  
```
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns="http://www.mulesoft.org/schema/mule/core"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd">
  <flow name="componentsFlow">
   <scheduler doc:name="Scheduler" disallowConcurrentExecution="true">
    <scheduling-strategy >
     <fixed-frequency frequency="1000"/>
    </scheduling-strategy>
   </scheduler>
  </flow>
</mule>
```

## `<fixed-frequency>` Properties
Attribute | Description | Example  
---|---|---  
`frequency` | Triggering frequency, relative to time unit. When set to `0` or a negative value, it switches to the default (1 minute). | `frequency="1000"`  
The time unit for the frequency and startDelay values: MILLISECONDS, SECONDS, MINUTES, HOURS, DAYS | `timeUnit="MILLISECONDS"`  
`startDelay` | Upon triggering the flow for the first time, Mule delays the first execution of the scheduler for a specific amount of time. This time period is expressed in the same time units as the frequency. | `startDelay="0"`  
```
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns="http://www.mulesoft.org/schema/mule/core"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd">
  <flow name="componentsFlow">
    <scheduler>
      <scheduling-strategy>
        <fixed-frequency startDelay="5" frequency="10" timeUnit="SECONDS"/>
      </scheduling-strategy>
    </scheduler>
    <logger message="my message"/>
  </flow>
</mule>
```

## `<cron>` Properties
For more complex scheduling strategies, you can use a cron expression.
Parameter | Default Value | Description | Example  
---|---|---|---  
`expression` | Use a cron expression for when to do a trigger. | `expression="1 1 1 1,7 * ?"`  
Time zone passed as system property, or in machine’s operating system. | Timezone in Java time zone format | `timeZone="America/Argentina/Buenos_Aires"`  
Example that uses a cron expression:
```
<?xml version="1.0" encoding="UTF-8"?>
<mule xmlns="http://www.mulesoft.org/schema/mule/core"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://www.mulesoft.org/schema/mule/core http://www.mulesoft.org/schema/mule/core/current/mule.xsd">
  <flow name="componentsFlow">
    <scheduler>
      <scheduling-strategy>
        <cron expression="0 0 12 * * ?"/>
      </scheduling-strategy>
    </scheduler>
    <logger message="my message"/>
  </flow>
</mule>
```

## See Also
  * Scheduler Endpoint (Trigger)