Few OS concept brush-up for interview
How to avoid Deadlocks
Deadlock doesn’t occur by keeping anyone condition false i.e.
1. Mutual Exclusion Condition: The resources involved are non-shareable. Meaning, At least one resource (thread) must be held in a non-shareable mode, that is, only one process at a time claims exclusive control of the resource. If another process requests that resource, the requesting process must be delayed until the resource has been released.
2. Hold and Wait Condition: There must exist a process that is holding a resource already allocated to it while waiting for additional resource that are currently being held by other processes.
3. No-Preemptive Condition: Resources cannot be removed from the processes are used to completion or released voluntarily by the process holding it.
4. Circular Wait Condition: The processes in the system form a circular list or chain where each process in the list is waiting for a resource held by the next process in the list.
Three-Way Handshake
A three-way handshake is primarily used to create a TCP socket connection. It works when:
- A client node sends a SYN data packet over an IP network to a server on the same or an external network. The objective of this packet is to ask/infer if the server is open for new connections.
- The target server must have open ports that can accept and initiate new connections. When the server receives the SYN packet from the client node, it responds and returns a confirmation receipt — the ACK packet or SYN/ACK packet.
- The client node receives the SYN/ACK from the server and responds with an ACK packet.
Upon completion of this process, the connection is created and the host and server can communicate.
Why IP is unreliable Service
IP is a unreliable protocol because it does not guarantee the delivery of a datagram to its destination. The reliability must be provided by the upper layer protocols likeTCP. IP does not support flow control, retransmission, acknowledgement and error recovery.
What is ARP & How does it work?
ARP stands for Address Resolution Protocol. When you try to ping an IP address on your local network, say 192.168.1.1, your system has to turn the IP address 192.168.1.1 into a MAC address. This involves using ARP to resolve the address, hence its name.
Systems keep an ARP look-up table where they store information about what IP addresses are associated with what MAC addresses. When trying to send a packet to an IP address, the system will first consult this table to see if it already knows the MAC address. If there is a value cached, ARP is not used.
If the IP address is not found in the ARP table, the system will then send a broadcast packet to the network using the ARP protocol to ask “who has 192.168.1.1”. Because it is a broadcast packet, it is sent to a special MAC address that causes all machines on the network to receive it. Any machine with the requested IP address will reply with an ARP packet that says “I am 192.168.1.1”, and this includes the MAC address which can receive packets for that IP.
