How to use the "wait" Policy statement to make multi-threading calls for an Azure API service operation?

The "wait" Policy Statement allows you to make multi-threading calls to external systems.

The "wait" statement has the following syntax:

<wait for="all|any"> 
    <send-request .../>
    <send-request .../>
	...
</wait>  

If for="any" is specified, the "wait" statement ends if any one of the child calls ends.

If for="all" is specified, the "wait" statement ends if all child calls end.

For example, the following policy makes two web service calls simultaneously and waits for both of them to finish:

<wait for="all">
  <send-request mode="new" response-variable-name="response1">  
    <set-url>http://dev.fyicenter.com/api/users/101</set-url>  
    <set-method>GET</set-method>  
  </send-request>  
  <send-request mode="new" response-variable-name="response2">  
    <set-url>http://dev.fyicenter.com/api/orders/202</set-url>  
    <set-method>GET</set-method>  
  </send-request>
</wait>  

⇒Policy to Control Backend Service

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