Synchronization and Concurrent Programming Concepts

Process Synchronization

• Producer-consumer problem: producer writes data, consumer reads data from shared memory, mutual exclusion is required to ensure simultaneous access is not allowed.

Programs

• Sequential programs: instructions are executed in sequence.
• Concurrent programs: 2 or more processes/threads are executed in parallel, each process is a sequential program itself.
• Multiprogramming: multiple programs appear to run simultaneously by rapidly switching tasks between programs instead of waiting for each program to finish.

Task Switching

• Task switching occurs voluntarily or in response to interrupts (e.g., from I/O devices).

Async Process Execution

• Processes have little to no control over the interleaving in multiprocessing systems.
• Each process progresses based on the availability of resources and OS decisions.

Internetworking

• Each device connected to any subnet has a unique address.
• Protocols are implemented to define how packets should be formatted and managed as they travel across different subnets.
• Devices like routers serve as the connection from one network to another.

Internet Protocol

• Every device connected to the internet has a unique 32-bit IP address.
• Rules are established on how data must be sent and received across the internet.
• IP allows sending of datagram packets even if devices are not directly connected.
• Address Resolution: converts human-readable internet addresses (www.example.com) into machine-readable network addresses.

Techniques to Alleviate IPV4 Shortage

• Classes Inter-Domain Routing (CIDR): assign IP addresses based on a specific prefix length.
• Use private IP addresses.
• Network Address Translation (NAT): multiple devices in a local network share a single IP address when accessing the internet.

Networking

• IP packet filtering: examines individual data packets based on their source and destination IP addresses.
• TCP gateway: controls and establishes the TCP connection by checking all requests.
• Java Object Serialization: flattens and represents external data of any single object or tree of objects to be transmitted/stored on a disk.

Remote Object Reference

• An identifier for a remote object that's valid throughout a distributed system.
• Must be uniquely generated.

External Data Representation

• Application programs store information via data structures, which must be flattened (converted to bytes) to be sent over the net.
• Marshalling: taking a collection of data items and converting them into a form suitable for transmission in a message.
• Unmarshalling: disassembling the message on arrival to produce an equivalent collection of data items at the destination.

OSI Layers

• Data Link: transmits packets between nodes.
• Network: transfers packets between computers in a specific network.
• Transport: message/data is partitioned into smaller packets and ensures they arrive correctly at the destination (TCP/UDP).
• Session: layer for failure detection, synchronizes data flow.
• Presentation: where encryption happens.
• Application: directly provides network services to users (HTTP, FTP, SMTP).

Packet Delivery

• Datagram Packet Delivery: may follow different routes and may arrive out of sequence, no setup required.
• Virtual Circuit Packet Delivery: virtual circuit setup is required by identifying a route from the source to destination.

Routing

• Uses a routing algorithm to determine the routes of packet transmission.

Congestion Control

• Networks have limits in terms of capacity, and congestion control is used to prevent data packet loss by sending signals to devices (like routers) along the nodes (routes) of the data packets.

Interference

• Occurs when 2 processes read and write in the shared variables in an unpredictable order, leading to unpredictable results.

Synchronization Problems

• Barrier Sync: multiple processes wait for each other to finish each iteration.
• Reader-Writer: group of producers and consumers add and remove tasks on a bounded buffer capacity.
• Dining Savages.

Distributed Systems

• Hardware/software components located at networked computers that communicate via message passing.
• Examples: web searching, MMORPGs.
• Representation of hardware elements of a distributed system that abstracts away specific details of the computer & networking technologies employed.
• Characteristics:
  • Concurrent execution.
  • Communication between components via message passing.

Learn about synchronization techniques like mutual exclusion for shared memory management, as well as the differences between sequential and concurrent programs. Understand the basics of multiprogramming and how it relates to executing processes in parallel.