viernes, 30 de abril de 2010

Java Readers and Writer. Mutual exclusion.

Think about this situation, you have a buffer and into the bufer has one data. We have several elements in this situation: One Writer, that provide tha data into the buffer, and many Readers, thtat need the data into the buffer; and one restriction, only one persona can read or write into the buffer at the same time.

In order to resolve this problem we can use a Monitor. A monitor is a Class that provide a mutual exclusion in this methods. To write this in Java, we can introduce the keyword synchronized in the method. For ejample, in Buffer.java:




We can see complete execution over Main class



Output:

run:
Reader 0 is waiting to get data (total buffer=0)
Reader 9 is waiting to get data (total buffer=0)
Reader 8 is waiting to get data (total buffer=0)
Reader 7 is waiting to get data (total buffer=0)
Reader 3 is waiting to get data (total buffer=0)
Reader 6 is waiting to get data (total buffer=0)
Reader 2 is waiting to get data (total buffer=0)
Reader 1 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 0 unlock
Reader 0 has read a data (buff=0)
........reader 9 unlock
Reader 9 is waiting to get data (total buffer=0)
Reader 4 is waiting to get data (total buffer=0)
Reader 5 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 8 unlock
Reader 8 has read a data (buff=0)
........reader 7 unlock
Reader 7 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 3 unlock
Reader 3 has read a data (buff=0)
........reader 6 unlock
Reader 6 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 2 unlock
Reader 2 has read a data (buff=0)
........reader 1 unlock
Reader 1 is waiting to get data (total buffer=0)
Reader 28 is waiting to get data (total buffer=0)
Reader 29 is waiting to get data (total buffer=0)
Reader 20 is waiting to get data (total buffer=0)
Reader 11 is waiting to get data (total buffer=0)
Reader 13 is waiting to get data (total buffer=0)
Reader 16 is waiting to get data (total buffer=0)
Reader 27 is waiting to get data (total buffer=0)
Reader 10 is waiting to get data (total buffer=0)
Reader 18 is waiting to get data (total buffer=0)
Reader 24 is waiting to get data (total buffer=0)
Reader 23 is waiting to get data (total buffer=0)
Reader 17 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 9 unlock
Reader 9 has read a data (buff=0)
........reader 4 unlock
Reader 4 is waiting to get data (total buffer=0)
Reader 21 is waiting to get data (total buffer=0)
Reader 22 is waiting to get data (total buffer=0)
Reader 19 is waiting to get data (total buffer=0)
Reader 12 is waiting to get data (total buffer=0)
Reader 25 is waiting to get data (total buffer=0)
Reader 26 is waiting to get data (total buffer=0)
Reader 14 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 5 unlock
Reader 5 has read a data (buff=0)
........reader 7 unlock
Reader 7 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 6 unlock
Reader 6 has read a data (buff=0)
........reader 1 unlock
Reader 1 is waiting to get data (total buffer=0)
Reader 15 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 28 unlock
Reader 28 has read a data (buff=0)
........reader 29 unlock
Reader 29 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 20 unlock
Reader 20 has read a data (buff=0)
........reader 11 unlock
Reader 11 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 13 unlock
Reader 13 has read a data (buff=0)
........reader 16 unlock
Reader 16 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 27 unlock
Reader 27 has read a data (buff=0)
........reader 10 unlock
Reader 10 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 18 unlock
Reader 18 has read a data (buff=0)
........reader 24 unlock
Reader 24 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 23 unlock
Reader 23 has read a data (buff=0)
........reader 17 unlock
Reader 17 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 4 unlock
Reader 4 has read a data (buff=0)
........reader 21 unlock
Reader 21 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 22 unlock
Reader 22 has read a data (buff=0)
........reader 19 unlock
Reader 19 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 12 unlock
Reader 12 has read a data (buff=0)
........reader 25 unlock
Reader 25 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 26 unlock
Reader 26 has read a data (buff=0)
........reader 14 unlock
Reader 14 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 7 unlock
Reader 7 has read a data (buff=0)
........reader 1 unlock
Reader 1 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 15 unlock
Reader 15 has read a data (buff=0)
........reader 29 unlock
Reader 29 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 11 unlock
Reader 11 has read a data (buff=0)
........reader 16 unlock
Reader 16 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 10 unlock
Reader 10 has read a data (buff=0)
........reader 24 unlock
Reader 24 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 17 unlock
Reader 17 has read a data (buff=0)
........reader 21 unlock
Reader 21 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 19 unlock
Reader 19 has read a data (buff=0)
........reader 25 unlock
Reader 25 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 14 unlock
Reader 14 has read a data (buff=0)
........reader 1 unlock
Reader 1 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 29 unlock
Reader 29 has read a data (buff=0)
........reader 16 unlock
Reader 16 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 24 unlock
Reader 24 has read a data (buff=0)
........reader 21 unlock
Reader 21 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 25 unlock
Reader 25 has read a data (buff=0)
........reader 1 unlock
Reader 1 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 16 unlock
Reader 16 has read a data (buff=0)
........reader 21 unlock
Reader 21 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 1 unlock
Reader 1 has read a data (buff=0)
........reader 21 unlock
Reader 21 is waiting to get data (total buffer=0)
The writer is writing data (buffer:1)
........reader 21 unlock
Reader 21 has read a data (buff=0)
The writer is writing data (buffer:1)
The writer is writing data (buffer:2)
The writer is writing data (buffer:3)
The writer is writing data (buffer:4)
The writer is waiting to write data. The buffer is full