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E.4.1 Pragma Asynchronous

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[This subclause introduces the pragma Asynchronous which allows a remote subprogram call to return prior to completion of the execution of the corresponding remote subprogram body.] 

Syntax

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The form of a pragma Asynchronous is as follows: 
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  pragma Asynchronous(local_name);

Legality Rules

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The local_name of a pragma Asynchronous shall denote either: 
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One or more remote procedures; the formal parameters of the procedure(s) shall all be of mode in;
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The first subtype of a remote access-to-procedure type; the formal parameters of the designated profile of the type shall all be of mode in;
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The first subtype of a remote access-to-class-wide type. 

Static Semantics

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{representation pragma (Asynchronous) [partial]} {pragma, representation (Asynchronous) [partial]} A pragma Asynchronous is a representation pragma. When applied to a type, it specifies the type-related asynchronous aspect of the type.

Dynamic Semantics

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{remote procedure call (asynchronous)} {asynchronous (remote procedure call)} A remote call is asynchronous if it is a call to a procedure, or a call through a value of an access-to-procedure type, to which a pragma Asynchronous applies. In addition, if a pragma Asynchronous applies to a remote access-to-class-wide type, then a dispatching call on a procedure with a controlling operand designated by a value of the type is asynchronous if the formal parameters of the procedure are all of mode in

Implementation Requirements

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Asynchronous remote procedure calls shall be implemented such that the corresponding body executes at most once as a result of the call. 
10.a
To be honest: It is not clear that this rule can be tested or even defined formally. 

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