16.2.4 RK Calls

The RK calls required by Zipcode are as follows:

• msg = xmalloc(int length) allocates a message buffer of length bytes and returns a pointer msg to it;
• xfree(char *msg) deallocates the message buffer pointed to by msg;
• xlength(char *msg) determines the length (in bytes) of a previously allocated or received message msg;
• msg = xrecv() receives a message without blocking , returning a pointer to the message if a message can be received and NULL if there is no message queued to the calling process;

• msg = xrecvb() blocks until a message can be received and returns a pointer to the message;

• xsend(char *msg, int node, int pid) sends a message pointed to by msg to the process pid on node node; and

• xmsend(char *msg, int count, int *dest) sends a message msg to multiple destinations specified by the integer array dest of length 2*count in the form { node0, pid0, node1, pid1, ...} .

It is important to note that xsend() and xmsend() deallocate the message buffer after sending the message; they are semantically analogous to xfree(). The receive functions xrecv() and xrecvb() are semantically analogous to xmalloc().

Zipcode-based programs are not to call any of these CE or RK functions directly. Both message passing and environment control are represented in Zipcode.