Synchronous &Asynchronous Models in ComputingBy: James Pauer

What is Asynchronous

What is synchronous?

Greek: prefix; no, absence of, without, lack of, not

Another Way

Basics of Synchronies Actions occur at specific times and

intervals Measured against a time reference, or a

clock signal Takes time to communicate with the

receiver beforehand Accommodates complex and larger

transmissions

Basics of Asynchronies Each byte holds its own signal bits

Each byte holds it’s own signal bits

Basics of Asynchronies Each byte holds it’s own signal bits Responds to another signal Not governed by a synchronized clock AKA “best effort” Simple small transmission

Connect to a modem / network Point-to-Point Protocol (PPP)

Authentication, encryption, compression PPPOE

In Computer science Transmission Threading Programming Language Circuits Data

Data integrity

In Computer science Transmission

Transmission (Synchronous)

No start/stop bits Synchronizes transmission speeds / clocks Meant for continuous flow of data High transfer rate Errors

Clock out of sync, eventually Bytes arriving at unknown time Dropped packets/lost bits

Solutions Re-synchronization Check digits

Check digit ISBN 10 ISBN 13 EAN UPC “036000241457”

Add odds, multiply by 3 Add evens Add the two results Mod 10 , minus 10

Transmission (Asynchronous)

Has start/stop bits

Intermittent flow of data

Arbitrary waiting time Parity

Error detection technique = check digit

Parity Bits

7 bits of data

(number of 1s)

8 bits including parity

even odd

0000000 (0) 00000000 10000000

1010001 (3) 11010001 01010001

1101001 (4) 01101001 11101001

1111111 (7) 11111111 01111111 Parity bit - 0 = true 1= false Zero is even

In Computer science Transmission Threading

Synchronous I/O

Synchronous I/O cont.

AKA “blocking I/O” Problems

Large delay times The I/O operation completes An I/O error occurs. The function CancelSynchronousIO was

called, terminating the thread The blocked thread is terminated by the

system; the process itself is terminated

Asynchronous I/O

Asynchronous I/O cont.

Continues to process non I/O related tasks AKA “non-Blocking I/O” or “overlapped I/O” Beneficial to:

Backup of a large database Slow communication links

Optimizes processing efficiency

In Computer science Transmission Threading Programming Language

Programming Languages(Synchronous)

Argos Atom Averest ChucK Esterel LabVIEW

LEA Lustre PLEXIL SIGNAL SOL SyncCharts

Programming Languages(Synchronous)

Often used for reactive systems Eg. Flight simulator AKA “real-time” systems

AKA “Synchronous Reactive Programming (SRP)”

“Logical Ticks” Sequence of ticks Computations assumed instantaneous

Programming Languages(Asynchronous)

AJAX (Asynchronous JavaScript and XML) Support asynchronous methods:

JavaScript Promises/A

C# / Visual Basic Await operator

C++ Task class, then

Windows Runtime Displaying a message dialog Working with the file system Sending/receiving data to/from the internet

In Computer science Transmission Threading Programming Language Circuits

Circuits (Synchronous)

Parts are synchronized Disadvantages

Larger circuits/clock propagation Heating/gate switching

Circuits (Asynchronous)

Parts are autonomous Wait for signals through data transfer protocols Benefits

Components can run at different speeds Uses less power Emits less heat

UART (Universal Asynchronous Receiver Transmitter) Translates data between parallel and serial

In Computer science Transmission Threading Programming Language Circuits Data

Data integrity

Data Integrity File synchronization

such as syncing a hand-held MP3 player to a desktop computer. Cluster file systems

which are file systems that maintain data or indexes in a coherent fashion across a whole computing cluster.

Cache coherency maintaining multiple copies of data in sync across multiple

caches. RAID

where data is written in a redundant fashion across multiple disks, so that the loss of any one disk does not lead to a loss of data.

Database replication, where copies of data on a database are kept in sync, despite possible large geographical separation.

Journaling, a technique to make sure that file metadata are updated on a disk in a coherent, consistent manner.