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Class jcsp.lang.ints.AlternativeInt

java.lang.Object
   |
   +----jcsp.lang.ints.AlternativeInt

public class AlternativeInt
extends Object

Description

The AlternativeInt class enables a CSProcess to wait for data to become available from one or more ChannelInts.

The select method performs the ChannelInt selection function. The method returns the index of the ChannelInt within the array which should be read from. The developer must then read from that ChannelInt. There are several versions of this method which perform the same basic functionality but provide extra features such as timeouts and guards. The method will return -1 if the method completes without any ChannelInts being ready to be read from.

NOTE: For those familiar with the OCCAM programming language the AlternativeInt class is equivalent to the PRI ALT construct. Example

Simple Alt

 import jcsp.lang.int.*;
 public class AltExample1 implements CSProcess {
   private AltingChannelInputInt in1;
   private AltingChannelInputInt in2;
   private ChannelOutputInt out;
   public AltExample1(AltingChannelInputInt in1, AltingChannelInputInt in2, ChannelOutputInt out) {
     this.in1 = in1;
     this.in2 = in2;
     this.out = out;
   }
   public void run() {
     AlternativeInt alt = new AlternativeInt();
     AltingChannelInputInt[] altChans = {
       in1,
       in2
     };
     while (true) {
       int index = alt.select(altChans);
       altChans[index].read();
       out.write(index)
     }
   }
 }

Alt with Timeout

 import jcsp.lang.int.*;
 public class AltExample2 implements CSProcess {
   private AltingChannelInputInt in1;
   private AltingChannelInputInt in2;
   private ChannelOutputInt out;
   public AltExample2(AltingChannelInputInt in1, AltingChannelInputInt in2, ChannelOutputInt out) {
     this.in1 = in1;
     this.in2 = in2;
     this.out = out;
   }
   public void run() {
     AlternativeInt alt = new AlternativeInt();
     AltingChannelInputInt[] altChans = {
       in1,
       in2
     };
     while (true) {
       switch (alt.select(altChans, 100)) {
         case 0:
           out.write(in1.read());
         break;
         case 1:
           out.write(in2.read());
         break;
         default:
           // do something like update the screen here
         break;
       }
     }
   }
 }

Alt with Skip

 import jcsp.lang.int.*;
 public class AltExample3 implements CSProcess {
   private AltingChannelInputInt in1;
   private AltingChannelInputInt in2;
   private ChannelOutputInt out;
   public AltExample3(AltingChannelInputInt in1, AltingChannelInputInt in2, ChannelOutputInt out) {
     this.in1 = in1;
     this.in2 = in2;
     this.out = out;
   }
   public void run() {
     AlternativeInt alt = new AlternativeInt();
     AltingChannelInputInt[] altChans = {
       in1,
       in2
     };
     boolean skip = false;
     while (true) {
       switch (alt.select(altChans, skip)) {
         case 0:
           skip = true;
           out.write(in1.read());
         break;
         case 1:
           skip = false;
           out.write(in2.read());
         break;
         default:
           // do something like update the screen here
         break;
       }
     }
   }
 }

Alt with Guards

 import jcsp.lang.int.*;
 public class AltExample4 implements CSProcess {
   private AltingChannelInputInt in1;
   private AltingChannelInputInt in2;
   private ChannelOutputInt out;
   public AltExample4(AltingChannelInputInt in1, AltingChannelInputInt in2, ChannelOutputInt out) {
     this.in1 = in1;
     this.in2 = in2;
     this.out = out;
   }
   public void run() {
     AlternativeInt alt = new AlternativeInt();
     AltingChannelInputInt[] altChans = {
       in1,
       in2
     };
     boolean[] altGuards = {
       false,
       false
     };
     boolean skip = false;
     int numRead = 0;
     int sum = 0;
     while (true) {
       altGuards[0] = (numRead < 10);
       altGuards[1] = (numRead = 10);
       switch (alt.select(altChans, altGuards)) {
         case 0:
           int i = in1.read();
           sum += i;
           numRead++;
         break;
         case 1:
           in2.read();
           out.write(sum);
           sum = 0;
           numRead = 0;
         break;
       }
     }
   }
 }

NOTE: There are also methods to perform Alt with Guards and Timeout and Alt with Guards and Skip

Author:: P.D.Austin

AlternativeInt()

select(AltingChannelInputInt[]): Returns the index of one of the ChannelInts which has data that can be read.
select(AltingChannelInputInt[], boolean): Returns the index of one of the ChannelInts which has data that can be read.
select(AltingChannelInputInt[], boolean[]): Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard.
select(AltingChannelInputInt[], boolean[], boolean): Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard.
select(AltingChannelInputInt[], boolean[], long): Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard.
select(AltingChannelInputInt[], boolean[], long, int): Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard.
select(AltingChannelInputInt[], long): Returns the index of one of the ChannelInts which has data that can be read.
select(AltingChannelInputInt[], long, int): Returns the index of one of the ChannelInts which has data that can be read.

AlternativeInt

 public AlternativeInt()

select

 public synchronized int select(AltingChannelInputInt c[])

Returns the index of one of the ChannelInts which has data that can be read. The method will block until one of the ChannelInts becomes ready. The index of the ChannelInt in the array will be returned.

Parameters:: c - the ChannelInts to be selected from

select

 public synchronized int select(AltingChannelInputInt c[],
                                long msecs)

Returns the index of one of the ChannelInts which has data that can be read. The method will block until either one of the ChannelInts becomes ready or the timeout expires (negative or 0 timeouts will timeout immediately). If one of the ChannelInts is ready the index of that ChannelInt in the array will be returned otherwise -1 will be returned to indicate that no ChannelInts are ready.

Parameters:: c - the ChannelInts to be selected from; msecs - the time in milli-seconds to wait for a ChannelInt to become ready

select

 public synchronized int select(AltingChannelInputInt c[],
                                long msecs,
                                int nsecs)

Parameters:: c - the ChannelInts to be selected from; msecs - the time in milli-seconds to wait for a ChannelInt to become ready; nsecs - the extra time above msecs to wait in nano-seconds

select

 public int select(AltingChannelInputInt c[],
                   boolean skip)

Returns the index of one of the ChannelInts which has data that can be read. If the skip flag is true the method will not block if no ChannelInts are ready otherwise it will block until one of the ChannelInts is ready. If one of the ChannelInts is ready the index of that ChannelInt in the array will be returned otherwise -1 will be returned to indicate that no ChannelInts are ready.

NOTE: This method enables the development of a polling programs which can consume extra processor time. Try to use one of the other select methods.

Parameters:: c - the ChannelInts to be selected from; skip - A Boolean indicating whether the method should block until data is ready

select

 public synchronized int select(AltingChannelInputInt c[],
                                boolean guard[])

Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard. The method will block until one of the ChannelInts becomes ready. The index of the ChannelInt in the array will be returned.

NOTE: The c and guard arrays must be of the same size.

Parameters:: c - the ChannelInts to be selected from; guard - the guards for the ChannelInts

select

 public synchronized int select(AltingChannelInputInt c[],
                                boolean guard[],
                                long msecs)

Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard. The method will block until either one of the ChannelInts becomes ready or the timeout expires (negative or 0 timeouts will timeout immediately). If one of the ChannelInts is ready the index of that ChannelInt in the array will be returned otherwise -1 will be returned to indicate that no ChannelInts are ready.

NOTE: The c and guard arrays must be of the same size.

Parameters:: c - the ChannelInts to be selected from; guard - the guards for the ChannelInts; msecs - the time in milli-seconds to wait for a ChannelInt to become ready

select

 public synchronized int select(AltingChannelInputInt c[],
                                boolean guard[],
                                long msecs,
                                int nsecs)

NOTE: The c and guard arrays must be of the same size.

Parameters:: c - the ChannelInts to be selected from; guard - the guards for the ChannelInts; msecs - the time in milli-seconds to wait for a ChannelInt to become ready; nsecs - the extra time above msecs to wait in nano-seconds

select

 public int select(AltingChannelInputInt c[],
                   boolean guard[],
                   boolean skip)

Returns the index of one of the ChannelInts which has data that can be read ignoring those ChannelInts which have a false guard. If the skip flag is true the method will not block if no ChannelInts are ready otherwise it will block until one of the ChannelInts is ready. If one of the ChannelInts is ready the index of that ChannelInt in the array will be returned otherwise -1 will be returned to indicate that no ChannelInts are ready.

NOTE: The c and guard arrays must be of the same size.

NOTE: This method enables the development of a polling programs which can consume extra processor time. Try to use one of the other select methods.

Parameters:: c - the ChannelInts to be selected from; guard - the guards for the ChannelInts; skip - A Boolean indicating whether the method should block until data is ready

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