Message Passing

SALSA actors use asynchronous message passing as their basic form of communication. A SALSA message handler is similar to a Java method. 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 token <-, 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 message 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 expression:

 
// Wrong! It does not compile!!!
// Assume 'a' is an actor reference.
a <- someObject.someHandler();
 
   

Message Passing in SALSA is by-value for objects, and by-reference for actors. 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.