edu.rice.hj.api

Interface HjEventCount

All Known Implementing Classes:

HjParEventCount, HjSeqEventCount

public interface HjEventCount

An eventcount is an object that keeps a count of the number of events in a particular class that have occurred so far in the execution of the system. Events are the executions of primitive operations of a process, and particularly the executions of advance, await, and read primitives constitute events. The advance, await, and read operations on the same event count may be concurrent.

Synchronization with Eventcounts and Sequencers. David P. Reed and Rajendra K. Kanodia. Communications of the ACM, Volume 22, Number 2 (February 1979), 115-123.

Author:

Shams Imam (shams@rice.edu)

Method Summary

Modifier and Type	Method and Description
void	advance() The primitive advance() is used to signal the occurrence of an event.
void	await(long v) Quite often, a process may not wish to execute until some event in a class in which it has interest has happened.
long	read() Return the current value of an eventcount.

Method Detail

advance

void advance()

The primitive advance() is used to signal the occurrence of an event. The effect of this operation is to increase the integer value of the eventcount by 1.

read

long read()

Return the current value of an eventcount. It equals the number of advance operations that have been performed on it. To be more precise, the value returned by read() counts all of the advance operations that precede the execution, and may or may not count those in progress during the read. Thus, although the value may be changing during the execution of the read primitive, the result of read() is a lower bound on the current value of E after the read, and an upper bound on the value of E before the read.

Returns:

the current value of an eventcount.

await

void await(long v)
    throws SuspendableException

Quite often, a process may not wish to execute until some event in a class in which it has interest has happened. Although that effect can be achieved by looping around an execution of a read() primitive until a specified value of the eventcount, E, is reached, it is more useful to provide a primitive that incorporates the waiting. Such a primitive would also provide the opportunity to avoid the busy form of waiting. Consequently, we define a primitive await(E, v) that suspends the calling process until the value of the eventcount E is at least v. Of course, as in all mechanisms designed for asynchronous processes, the await primitive may not return immediately once the vth advance on E is executed; the only guarantee is that at least v advances have been performed by the time await(E, v) returns.

Parameters:

v - The value of the eventcount to wait until

Throws:

SuspendableException