Fundamentals of process management

Process management is also called processor management

Procedures and processes

• The order of execution of the program ：1-2-3,1 yes 2 The precursor of ,2 yes 1 In the subsequent
• The program with no precursor relationship of the same job or the program segments of different jobs can be executed in parallel .
• The characteristics of concurrent execution of programs ： Lost the closeness of the program , The execution sequence of the program and the machine is no longer one-to-one correspondence , The mutual restriction of concurrent programs

Process composition

• pcb Is the only criterion for the existence of a process
• Program ： A program can be shared and executed by multiple processes at the same time , Then this part should be compiled in the form of pure code , The program cannot be modified during execution
• data ： The data part includes the data required for program execution and the work area , This part can only be used by one process , Is the modifiable part of the process

State of process

• Three state model

function ： When a process is running on the processor
be ready ： A process is ready for everything , Ready to run
Blocking ： When a process is running, it needs to wait for something to run

Five state model

establish ： Created but not submitted
End ： When the process is finished , Free memory

Pending state

Active and ready ： Processes can be scheduled in main memory
Stand still ： The process is switched to secondary storage , Only wait for a location in main memory , Will be scheduled , Or it has a higher priority
Active blocking ： The process is in main memory , Once the waiting event is completed , Enter ready
Stand still ： It's been blocked for too long , Will be switched to secondary storage , Only let the waiting event complete , Only when it is static and ready , Wait for opportunities to be active and ready

Process control

All processes from creation to extinction are effectively controlled
Process control is implemented by primitives in the operating system kernel

Interprocess communication

• Synchronization and mutual exclusion
• Sync ： Inter process coordination ,a Process complete ,b Process start
• Mutually exclusive ： You can't take mine
• Management principles ： Enter when you are free , No time to wait , Limited waiting , Let the right waiting
• Limited waiting ： To ensure that the process enters the critical zone in a limited time
• Let the right waiting ： When the process cannot enter the critical zone , Let go
• Semaphore mechanism ： public ： Mutually exclusive ,1 Private use ; Sync 0

Advanced communication primitives

• Shared storage mode ： Processes communicating with each other share some data structures to realize communication
• Messaging mode ： Communicate through primitives
• Pipeline communication ： adopt pip file , Write process and read process

Tube side

• Centralize resources , Abstract the resources in the system .
• The tube side is made of ： Shared data , A collection of operations that can be performed by concurrent processes on shared data , The initial code and access rights consist of .

Process scheduling

• Advanced scheduling ： Advanced scheduling is also called ： Long scheduling , Admission scheduling , Job scheduling . Put the process into the ready state
• Intermediate dispatch ： Also called ： Medium range scheduling , Swap scheduling , Drop the process of the swap area to run , Or throw the blocked state to the exchange area , Make way for other processes
• Low level scheduling ： Also called short-range scheduling or process scheduling , Drop the process in memory to run
• Scheduling algorithm ：
• First come, first served ： Who will use it first
• Time slice rotation ： Fixed time slice ： The time slices allocated to each process are equal , Variable time slice ： Change according to the actual situation
• Priority scheduling ： Schedule according to priority , Static priority ： A priority will be created at the beginning , Can't change , Dynamic priority ： It can change
• Multi level feedback scheduling ： The highest priority queue can run first
• Process priority determination ：
• about I/O Type process , Topmost queue , Computational process , Lowest level queue ,I/O Not many times , Mainly cpu The process of , At the completion of I/O after , Priority return I/O Queue of process end
  Deadlock
• Yes 2 A resource , One for one , But they all want to rob each other , It will form a loop , Cause a deadlock
• Deadlock solution ：
• Pre static distribution ： Request all resources at once , Don't give them a chance
• Orderly allocation of resources ： Sort the resources in order , Don't let them form a loop