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Operating System Processes

A process is defined as a program in execution which means that it must be active rather than passive. A process may include several distinct types of temporary data including function parameters, return addresses, and local variables. A process is also comprised of four sections: stack, heap, data, and text. 

Whenever a process is executed, it changes its state and may only hold one state at a time. The list below shows all the potential states that a process may be in. 

  • New - The process is being created. 
  • Running - Instructions are being executed. 
  • Waiting - The process is waiting for some event to occur (such as an I/O completion or reception of a signal). 
  • Ready - The process is waiting to be assigned to a processor. 
  • Terminated - The process has finished execution." 

A process control block, also known as a task control block "serves as the repository for any information that may vary from process to process." (Silberschatz et al. 2014) The process control block is comprised of seven parts including the process state, program counter, CPU registers, CPU – scheduling information, memory – management information, accounting information, and I/O status information. It also contains all the necessary information required to keep track of a process throughout its execution phase.  

A single thread will only allow one task to be performed at a given time. According to Silberschatz et al. 2014 “If a process has multiple threads of control, it can perform more than one task at a time.” Multithreaded processes can have numerous stacks and registers compared to a single thread that only contains one of each. Regarding thread models, there are three distinct ways that a thread can maintain a relationship with a kernel such as: 

  • Many-to-One – Utilizes multiple user-level threads to one kernel thread. 
  • One-to-One – Utilizes one user-level thread to one kernel thread. 
  • Many-to-Many – Utilizes multiple user-level threads to multiple kernel threads. 

To accurately understand the critical-section problem we need to understand what the critical-section is. The critical section is where a process may be altering different types of data. When a process is within its critical-section no additional process can be within the critical-section at the same time. Therefore, the critical-section problem is "to design a protocol that the processes can use to cooperate” where “each process must request permission to enter its critical section" (Silberschatz et al. 2014) A software solution used to help alleviate the critical-section problem is “Peterson’s Solution” Peterson’s solution solves the critical-section problem by allowing two different processes to alternate between their critical-section and their remainder section.  


References 

Silberschatz, A., Galvin, P. B., & Gagne, G. (2014). Operating system concepts essentials (2nd ed.). Retrieved from https://redshelf.com/



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