Write an algorithm for shared and exclusive locking. How does granularity affect this algorithm?

Question

What will be an ideal response?

Answer 1

read_lock(X):
B: if LOCK (X) = "unlocked"

then begin
LOCK (X) = "readlocked";
noOfReads(X) = 1
end
else if LOCK(X) = "readlocked"
then noOfReads(X) = noOf Reads(X) + 1
else begin
wait (until LOCK (X) = "unlocked" and
the lock manager wakes up the transaction);
goto B
end

write_lock (X):
B: if LOCK (X) = "unlocked"

then LOCK (X) = "writelocked"
else begin
wait (until LOCK(X) = "unlocked" and
the lock manager wakes up the transaction);
goto B
end;

unlock_item (X):

if LOCK (X) = "writelocked"
then begin
LOCK (X) = "unlocked";
wakeup one of the waiting transactions, if any
end
else if LOCK(X) = "readlocked"
then begin
noOfReads(X) = noOfReads(X) 1;
if noOfReads(X) = 0
then begin
LOCK (X) = "unlocked";
wakeup one of the waiting transactions, if any
end;
end;

Algorithm 1 Locking and unlocking operations for twomode (readwrite or sharedexclusive)

locks