[Chapter 3] Process

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Processs Concept

• The Process
• Process State
• Process Control Block
• Threads

Process Scheduling

• Scheduling Queue
• CPU Scheduling
• Context Swtich

Operation on Processes

• Process Creation
• Process Termination

InterProcess Communication

IPC in Shared-Memory Systems

IPC in Message-Passing Systems

Examples of IPC Systems

• POSIX Shared Memory
• Mach Message Passing
• Windows
• Pipes

Communication in Client-Server Systems

• Socket
• Remote Procedure Calls, RPS
• Android RPC

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❔ Processes ?

Process Concept ?

• A process is an instance of a program in execution.

• Batch systems work in terms of "jobs". Many modern process concepts are still expressed in terms of jobs, and the two terms are often used interchangeably.

  • Process memory is divided into four sections

    • The text section comprise the compiled program code, read in from non-volatile storage when the program is launched.
    • The data section stores global and static variables, allocated and initialized prior to executing main.
    • The heap is used for local variables. Space on the stack is reserved for local variables when they are declared, ad the space is freed up when the variables go out of scope. Note that the stack is also used for function return values, and the exact mechanisms of stack management may be language specific.
    • Note that the stack and the heap start at opposite ends of process's free space and grow towards each other. If you should event meet, then either a stack overflow error will occur, or else a call to new or malloc will fail due to insufficient memory available.

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❔ PCB (Process Control Block)

• Process State : new, ready, running, waiting or halted
• Program counter : The counter indicates the address of the next instruction to be executed for this process.
• CPU registers : The registers vary in number and type, depending on the computer architecture. They include accumulators, index registers, stack pointers and general-purpose registers, plus any condition code information. Along with the program counter, this state information must be saved when an interrupt occurs, to allow the process to be continued correctly afterwards.
• CPU-scheduling information : This information includes a process priority, pointers to scheduling queues, and any other scheduling parameters.
• Memory-management information : This information may include such information such as the value of the base and limit registers, the page tables, or the segment tables, depending on the memory system used by the operating system.
• Accounting informations : This information includes the amount of CPU and real time used, time limits account numbers, job or process numbers, and so on
• I/O status information : The information includes the list of I/O devices allocated to the process, a list of open files, and so on.