JR Language Reference

This page provides a short syntactical reference to the JR language and its various constructs for concurrent programming. The meaning of the constructs is not explained in any great detail, we refer to the lecture notes for that.

First of all, JR is an extension of Java. This means that every valid Java program is also a JR program. You can you all the features and libraries of Java when programming in JR. In addition to the features of Java, JR provides a number of language constructs for concurrent programming.

Note that you should not use Java's constructs or libraries for concurrency when programming in JR. Bad things will happen if you do.

Semaphores

JR provides semaphores as follows.

Declaring a semaphore:	`sem s = 1;`
Operations on semaphores:	`P(s);`
	`V(s);`
	`s.length();`

Operations

JR provides operations which is a generalization of message passing and provides several ways of communications.

Declaring an operation:	`op void channel();`
	`op int fac(int n);`

Invoking operations

Assuming we have an operation declared as follows: op int fac(int n);

Asynchronous:	`send fac(3);`
Synchronous (ignoring the result):	`call fac(3);`
Synchronous (ignoring the result):	`fac(3);`
Synchronous:	`int n = fac(3);`

Servicing operations

By a method:	`op int fac(int n) { if (n==0) return 1 else return n * fac(n-1); }`
By receive statement(assuming we have declared a variable `int a;`):	`receive fac(a);`
By input statement:	`inni int fac(int n) { return 5; }`
Examining the number of messages in an operation:	`fac.length()`

Additional constructs in the input statement