First In First Out Queue

Introduction to FIFO’s
As we saw earlier, the first in first out circular queue (FIFO) is quite useful for implementing a buffered I/O interface. It can be used for both buffered input and buffered output. The order preserving data structure temporarily saves data created by the source (producer) before it is processed by the sink (consumer). The class of FIFO’s studied in this section will be statically allocated global structures.

Because they are global variables, it means they will exist permanently and can be carefully shared by more than one program. The advantage of using a FIFO structure for a data flow problem is that we can decouple the producer and consumer threads. Without the FIFO we would have to produce 1 piece of data, then
process it, produce another piece of data, then process it. With the FIFO, the producer thread can continue to produce data without having to wait for the consumer to finish processing the previous data. This decoupling can significantly improve system performance.

You have probably already experienced the convenience of FIFO’s. For example, you can continue to type another commands into the DOS command interpreter while it is still processing a previous command. The ASCII codes are put (calls PutFifo) in a FIFO whenever you hit the key. When the DOS command interpreter is free it calls GetFifo for more keyboard data to process. A FIFO is also used
when you ask the computer to print a file. Rather than waiting for the actual printing to occur character by character, the print command will PUT the data in a FIFO. Whenever the printer is free, it will GET data from the FIFO. The advantage of the FIFO is it allows you to continue to use your computer while the printing occurs in the background. To implement this magic of background printing we will need interrupts.
There are many producer/consumer applications. In the following table the processes on the left are producers that create or input data, while the processes on the right are consumers which process or output data.

You have probably already experienced the convenience of FIFO’s. For example, you can continue to type another commands into the DOS command interpreter while it is still processing a previous command. The ASCII codes are put (calls PutFifo) in a FIFO whenever you hit the key. When the
DOS command interpreter is free it calls GetFifo for more keyboard data to process. A FIFO is also used when you ask the computer to print a file. Rather than waiting for the actual printing to occur character by character, the print command will PUT the data in a FIFO. Whenever the printer is free, it will GET data from the FIFO. The advantage of the FIFO is it allows you to continue to use your computer while the
printing occurs in the background. To implement this magic of background printing we will need interrupts.

There are many producer/consumer applications. In the following table the processes on the left are producers that create or input data, while the processes on the right are consumers which process or output data.