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Let us discuss about the below two types of message passing systems, which are as follows −Client Server Message PassingConsider an application that you are trying to read data from the filesystem. That means here the application is a client requesting the data from a server. This client or server model introduces many process states that are associated with message passing.Initially, the server has to wait for a message to arrive from another system which is present somewhere else. At this point, the server is said to be receive-blocked.When a message is received, the server enters into the READY state, ... Read More
Whenever the transaction between user and kernel mode is required, a context switch is not necessary; simply a mode transition is not a context switch. Because, depending on the operating system, a context switch may also take place at this time.Let us see the major steps of Context SwitchingThe values of the CPU registers are generally saved in the process table of the process which was running before the clock interrupt occurred.To run next the registers are loaded from the process and picked by the CPU scheduler.Consider a multi-programmed single processor system, the context switches occur frequently so that all ... Read More
Let us begin by understanding what process suspension is.Process suspensionWhenever the processes in main memory are entered into the blocked state, the operating system suspends one process by putting it in the Suspended state and transferring it to disk. The free space present in the memory is used for bringing another process.Many OS are around Ready, Running, Blocked states. But generally, there is one more state in the operation of an OS that is suspended.If any process is not occupying the main memory which is in a Ready state, OS swaps one of the blocked processes out onto the Suspend ... Read More
Let us begin by understanding what a scheduler is.SchedulerIt is used for handling the process and makes scheduling for the process. The main task of the scheduler is to select the process and make order of process, and to decide which process runs first.Types of SchedulersThere are three different types of schedulers, which are as follows −Long term schedulerLong term scheduling is performed when a new process is created, if the number of ready processes in the ready queue becomes very high, and then there is an overhead on the operating system, for maintaining long lists, containing switching and dispatching ... Read More
Process control block (PCB) is used by the operating system to store different information about the process including process state, registers, program counter, registers etc. It plays an important role when a context switching happens (the current process is pre-empted by another process with higher priority).The important information stored in PCB includes the following −Process Number (PID) − Used to uniquely identify each process.Program counter − It stores the address of the next instruction which is to be executed.Register Info − Includes different CPU registers such as base, accumulators and general purpose register.State − State in the life cycle of ... Read More
Let us understand the privileged instructions in an operating system.Privileged instructionsThese are called machine level instructions that are executed when the processor is in privileged mode.The examples include the following −Shut down the systemChange the contents of a control register.Jump into kernel code.Sending commands to I/O devices.The processor is said to be in privileged mode when the functions in the OS kernel are executing.Suppose an attempt is made to execute a privileged instruction in non-privileged mode which causes a run-time error.Generally the user mode of the operating system is called non-privileged mode and kernel mode of the operating system is ... Read More
The five process states in the Linux kernel are as follows −Running − This is a state where a process is either in running or ready to run. It is the most active state of all. In this state, the process is getting system resources.Interruptible − This state is a blocked state of a process which waits for an event or a particular time slot.Uninterruptible − It is also a blocked state and it has a timeout value before going to sleep. It will awake when the timeout value sets off.Stopped − Once the process is completed, this state occurs ... Read More
Let us begin by understanding the types of process states.Types of Process StatesThere are different types of Process States which are as follows −New − The process is about to be created in this state but not yet created, it is the program which is present in secondary memory that will be picked up by OS to create the process.Ready − The process enters the ready state after the creation of a process that means the process is loaded into the main memory.Running − The process is chosen by the CPU for instructions and the executions within the process and ... Read More
A while loop is an indefinite loop that can be modified to run for a finite number of iterations based on the condition we provide.In Lua, the while condition is tested first. If the condition turns out to be false, then the loop ends, otherwise, Lua executes the body of the loop and repeats the process.Syntaxwhile( condition ){ // do this }ExampleConsider the example shown below −a = {1, 2, 3, 4, 5} local i = 1 while a[i] do print(a[i]) i = i + 1 endOutput1 2 3 4 5It ... Read More
There are functions in Lua that accept a variable number of arguments. These are very helpful in cases where we want to run the same function with many different arguments that might vary in length. So, instead of creating a different function, we pass them in a variable arguments fashion.Syntaxfunction add(...) -- function code endIt should be noted that the three dots (...) in the parameter list indicate that the function has a variable number of arguments. Whenever this function will be called, all its arguments will be collected in a single table, which the function addresses ... Read More