N blocks of storage,
Consider a system with N blocks of storage, each of which holds one unit of information (e.g. an integer, character, or employee record). Initially, these blocks are empty and are linked onto a list called freelist. Three threads communicate using shared memory in the following manner:
Shared Variables: freelist, list-1, list-2: block (where block is some data type to hold items)
Thread-1
var b: pointer to type block;
while (1)
{
b:= unlink(freelist);
produce_information_in_block(b);
link(b, list1);
}
Thread-2
var x,y: pointer to type block;
while (1)
{
x:=unlink(list-1);
y:=unlink(freelist);
use_block_x_to_produce info_in_y(x, y);
link(x, freelist);
link(y, list-2);
}
Thread-3
var c: pointer to type block;
while(1)
{
c:=unlink(list-2);
consume_information_in_block(c);
link(c, freelist);
}
Using the POSIX library, rewrite the code for the threads, using semaphores to implement the necessary mutual exclusion and synchronization. The solution must be deadlock-free and concurrency should not be unnecessarily restricted.
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