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OS (Operating System)
Process Description and Control
- The concept features ① process, process
- Process control block : (Process Control Block PCB for short) system using PCB basic conditions described processes and activities.
- Process : a program segment, the data segment and associated PCB process entity three parts.
- Definition of the process: the process is the process of running the process entity, the system is an independent unit of resource allocation and scheduling.
- The process features : dynamic (static program is to be distinguished from the process), concurrency, independence, asynchronous nature.
- Five states process : Create state, ready state, execution state, blocking state and termination state.
- PCB information : a process identifier, the processor status, process scheduling information and process control information.
- ② Process Control
- Create a process caused by an event : user login, job scheduling, service and application requests.
- Creating process : application blank PCB, allocate the resources required to run the new process, initialization PCB, process ready queue if there are vacancies, insert the new process.
- Caused the process to terminate the event : normal end, abnormal end, outside intervention.
- Terminating the process : it is terminated a PCB retrieval identifier from the collection out of the PCB, the process is terminated (including its sub-process), which is provided schedule flag is true, all the resources to return, the PCB is removed from the queue, waiting for the next create.
- Cause the process to block and wake-up events : a request to the system resources fails, wait for the completion of certain operations, new data has not yet arrived, waiting for the arrival of new tasks.
- Proactive behavior blocking is the process, the command line is suspended
- If you call blocking in the process of primitive (computer language), we must arrange a wake-up process with the primitive phase of cooperation, so as to awaken the blocked process.
- Suspend the process : the process of checking to be suspended state, if the active ready will be replaced still in place, if the obstruction blocking instead still active, the process PCB copy to a designated area of memory, if the process is executing, it won re-scheduling (because the processor is only one or a few, can not let the suspended process occupied processor).