Message Passing

To achieve more parallelism, SALSA uses message passing. A SALSA method is named a message handler.

Message passing in SALSA is implemented by asynchronous message delivery with dynamic method invocation. The following example shows how an actor sends a message to itself. Note that it is not a JAVA method invocation:

 
handler();  // equivalent to "self <- handler();"
 
   

Another type of message passing statement requires a target (an actor reference), a reserved key word <-, and a message handler with arguments to be sent. For instance, an actor can send a message to the standardOutput actor as follows:

 
// send a method println() with an argument "Hello World", 
// to the actor standardOutput.
standardOutput <- println("Hello World"); 
 
   

Note that the following expression is illegal because it is neither a JAVA method invocation nor a message passing:

 
// Wrong! It does not compile!!!
self <- someObject.someHandler();
 
   

To avoid unexpected race conditions by accessing the passed arguments, messages of SALSA enforces pass-by-value for every object, and pass-by-reference for every actor. Any object passed as an argument is cloned at the moment it is sent, and the cloned object is then sent to the target actor.