org.jcsp.lang
Interface ChannelInputInt

All Superinterfaces:

Poisonable

All Known Subinterfaces:

SharedChannelInputInt

All Known Implementing Classes:

AltingChannelInputInt

public interface ChannelInputInt
extends Poisonable

This defines the interface for reading from object channels.

A reading-end, conforming to this interface, is obtained from a channel by invoking its in() method.

Description

ChannelInput defines the interface for reading from object channels. The interface contains three methods: read, startRead and endRead. The read and startRead methods block until an Object has been written to the channel by a process at the other end. If an Object has already been written when this method is called, the method will return without blocking. Either way, the methods return the Object sent down the channel.

When a read completes, the matching write method (invoked by the writing process) also completes. When a startRead completes, the matching write method does not complete until the reader process invokes an endRead. Actions performed by the reader in between a startRead and endRead make up an extended rendezvous.

ChannelInputInt variables are used to hold integer channels that are going to be used only for input by the declaring process. This is a security matter -- by declaring a ChannelInputInt interface, any attempt to output to the channel will generate a compile-time error. For example, the following code fragment will not compile:

 void doWrite (ChannelInputInt c, int i) {
   c.write (i);   // illegal
 }
 

When configuring a CSProcess with input integer channels, they should be declared as ChannelInputInt (or, if we wish to be able to make choices between events, as AltingChannelInputInt) variables. The actual channel passed, of course, may belong to any channel class that implements ChannelInputInt (or AltingChannelInputInt).

Example

Discard data

 void doRead (ChannelInputInt c) {
   c.read ();                       // clear the channel
 }
 

Author:

P.D. Austin and P.H. Welch and N.C.C.Brown

See Also:

AltingChannelInputInt, SharedChannelInputInt, ChannelOutputInt

Method Summary

void	endRead() End an extended rendezvous.
int	read() Read an int from the channel.
int	startRead() Begin an extended rendezvous read from the channel.

Methods inherited from interface org.jcsp.lang.Poisonable

poison

Method Detail

read

int read()

Read an int from the channel.

Returns:

the integer read from the channel

startRead

int startRead()

Begin an extended rendezvous read from the channel. An extended rendezvous is not completed until the reader has completed its extended action. This method starts an extended rendezvous. When a writer to this channel writes, this method returns what was sent immediately. The extended rendezvous continues with reader actions until the reader invokes endRead. Only then will the writer be released (from its write method). The writer is unaware of the extended nature of the communication.

The reader process must call endRead at some point after this function, otherwise the writer will not be freed and deadlock will probably follow.

The reader process may perform any actions between calling startRead and endRead, including communications on other channels. Further communications on this channel, of course, should not be made.

An extended rendezvous may be started after the channel's Guard has been selected by an Alternative (i.e. startRead instead of read).

Returns:

The object read from the channel

endRead

void endRead()

End an extended rendezvous. It must be invoked once (and only once) following a startRead.