Programming :: Algorithm - File System Block Number For Immediate Read

algorithm:breada
input: file system block number for immediate read
file system block number for asynchronous read
output:buffer containing data for immediate read {
if(first block not in cache) {
get buffer for first block
if(buffer data not valid)
initiate disk read }
if(second block not in cache) {
get buffer for second block)
if(buffer data valid) //line 1
release buffer else
initiate disk read //line 2 }
if(first block was originally in cache) //line 3 {
read first block
return buffer }
sleep (event first buffer contains valid data)
return buffer }

Here is an algorithm for block read algorithm. I have problem in
line 1: If buffer data is valid why is it releasing the buffer?
line 2: If buffer data valid why is it initiating disk read. It should have read directly from buffer?
line 3: It should be the first condition as if it is there in cache then it should return it without delay?