1.2mm Printed PCB Board Red Ink 22F Half Fiberglass Flame Retardant

 

Process control block PCB function:
In order to facilitate the system to describe and manage the running of processes, a special data structure is defined at the core of the OS for each process -- ProcessControlBlock (PCB).As a part of the process entity, PCB records all the information needed by the operating system to describe the current situation of the process and manage the operation of the process. It is the most important recording data structure in the operating system.The purpose of the PCB is to make a program (including data) that cannot run independently in a multiprogram environment become a basic unit that can run independently, a process that can execute concurrently with other processes.

(1) PCB as a symbol of independent operation of the basic unit.When a program (including data) are configured after the PCB, it means it is already a can run independently in a multiprogramming environment, the basic unit of the legal, also has the power to obtain OS services, such as open files in the file system, the request for the I/O devices in the system, and communicate with other related processes.Therefore, when the system creates a new process, it sets up a PCB for it.When the process ends, it recycles its PCB, and the process dies.The system is aware of the existence of processes through the PCB.In fact, the PCB has become the only sign that the process exists in the system.

(2) PCB can realize discontinuous operation mode.In the multiprogram environment, the program is run by the stop-start intermittent mode.When a process pauses due to blocking, it must retain information about the CPU scene at which it was running.With the PCB in place, the system can store CPU field information in the PCB of the interrupted process for use when the process is scheduled to resume the CPU field again.Thus, it can be clear again that in the multi-program environment, as a static program in the traditional sense, because it does not have the means to protect or preserve its own running site, it cannot guarantee the reproducibility of its running results, so it loses the significance of running.

(3) PCB provides the information needed for process management.When the scheduler dispatches to a process to run, the corresponding program and data can only be found according to the initial address pointer of the program and data recorded in the process PCB in memory or external memory.In the process of running, when you need to access files in the file system or I/O devices, you also need to use the information in the PCB.In addition, you can also know all the resources required by the process according to the resource list in the PCB.It can be seen that in the whole life cycle of the process, the operating system always implements the control and management of the process according to the PCB.

(4) PCB provides the information needed for process scheduling.Only processes that are in a ready state can be scheduled for execution, and the PCB provides information about the state of the process.If the process is in the ready state, the system inserts it into the process ready queue and waits for the scheduler to dispatch it.In addition, other information of the process is often needed during scheduling. For example, in the priority scheduling algorithm, the priority of the process needs to be known.In some fairer scheduling algorithms, you also need to know the wait time of the process, the events that have been executed, and so on.

(5) PCB realizes synchronization and communication with other processes.Process synchronization mechanism is used to realize the coordinated operation of various processes. When adopting the semaphore mechanism, it requires that each process should be set up with a corresponding semaphore for synchronization.There are also areas or communication queue Pointers for process communication in PCB.
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Copyright Notice: This article is the original work of Jiao Mubai, a CSDN blogger, under the CC 4.0 BY-SA copyright agreement. Please attach the link of the original source and this notice.
The original link: https://blog.csdn.net/jiaomubai/article/details/89683772

Ping You Industrial Co.,Ltd
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