CSP for Java
(JCSP) 1.1-rc4

org.jcsp.lang
Interface One2AnyChannel

All Known Subinterfaces:
FilteredOne2AnyChannel

public interface One2AnyChannel

This defines the interface for a one-to-any Object channel, safe for use by one writer and many readers.

The only methods provided are to obtain the ends of the channel, through which all reading and writing operations are done. Only an appropriate channel-end should be plugged into a process – not the whole channel. A process may use its external channels in one direction only – either for writing or reading.

Actual channels conforming to this interface are made using the relevant static construction methods from Channel. Channels may be synchronising, buffered, poisonable or both (i.e. buffered and poisonable).

Description

One2AnyChannel is an interface for a channel which is safe for use by many reading processes but only one writer. Reading processes compete with each other to use the channel. Only one reader and the writer will actually be using the channel at any one time. This is managed by the channel – user processes just read from or write to it.

Please note that this is a safely shared channel and not a broadcaster. Currently, broadcasting has to be managed by writing an active process (see DynamicDelta for an example).

All reading processes and the writing process commit to the channel (i.e. may not back off). This means that the reading processes may not ALT on this channel.

The default semantics of the channel is that of CSP – i.e. it is zero-buffered and fully synchronised. A reading process must wait for the matching writer and vice-versa.

The static methods of Channel construct channels with either the default semantics or with buffering to user-specified capacity and a range of blocking/overwriting policies. Various buffering plugins are given in the org.jcsp.util package, but careful users may write their own.

The Channel methods also provide for the construction of Poisonable channels and for arrays of channels.

Implementation Note and Caution

Fair servicing of readers to this channel depends on the fair servicing of requests to enter a synchronized block (or method) by the underlying Java Virtual Machine (JVM). Java does not specify how threads waiting to synchronize should be handled. Currently, Sun's standard JDKs queue these requests - which is fair. However, there is at least one JVM that puts such competing requests on a stack - which is legal but unfair and can lead to infinite starvation. This is a problem for any Java system relying on good behaviour from synchronized, not just for these 1-any channels.

Author:
P.D. Austin and P.H. Welch
See Also:
Channel, One2OneChannel, Any2OneChannel, Any2AnyChannel, ChannelDataStore

Method Summary
 SharedChannelInput in()
          Returns the input end of the channel.
 ChannelOutput out()
          Returns the output end of the channel.
 

Method Detail

in

SharedChannelInput in()
Returns the input end of the channel.


out

ChannelOutput out()
Returns the output end of the channel.


CSP for Java
(JCSP) 1.1-rc4

Submit a bug or feature to jcsp-team@kent.ac.uk
Version 1.1-rc4 of the JCSP API Specification (Copyright 1997-2008 P.D.Austin and P.H.Welch - All Rights Reserved)
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