1CSE 120CSE 120Principles of Operating Principles of Operating SystemsSystemsSystemsSystemsWinter 2007Winter 2007Lecture 3: ProcessesLecture 3: ProcessesKeith Marzullo and Geoffrey M. VoelkerKeith Marzullo and Geoffrey M. VoelkerProcessesProcessesz This lecture starts a class segment that covers processes, threads, and synchronizationprocesses, threads, and synchronization These topics are perhaps the most important in this class. You can rest assured that they will be covered in the exams.z Today’s topics are processes and process management What are the units of execution?How are those units of execution represented in the OS?January 16, 2007 CSE 120 – Lecture 3 – Processes 2How are those units of execution represented in the OS? How is work scheduled in the CPU? What are the possible execution states of a process? How does a process move from one state to another?2The ProcessThe Processz The process is the OS abstraction for executionIt is the unit of executionIt is the unit of execution It is the unit of scheduling It is the dynamic execution context of a programz A process is sometimes called a job or a task or a sequential processz A sequential process is a program in executionIt defines the sequential instructionatatime execution of aJanuary 16, 2007 CSE 120 – Lecture 3 – Processes 3It defines the sequential, instruction-at-a-time execution of a program Programs are static entities with the potential for executionProcess ComponentsProcess Componentsz A process contains all of the state for a program in executionexecution An address space The code for the executing program The data for the executing program An execution stack encapsulating the state of procedure calls The program counter (PC) indicating the next instruction A set of general-purpose registers with current valuesJanuary 16, 2007 CSE 120 – Lecture 3 – Processes 4 A set of operating system resources» Open files, network connections, etc.z A process is named using its process ID (PID)3Process Address SpaceProcess Address SpaceStack0xFFFFFFFFStatic DataHeap(Dynamic Memory Alloc)AddressSpaceSPJanuary 16, 2007 CSE 120 – Lecture 3 – Processes 50x00000000Code(Text Segment)Static Data(Data Segment)PCProcess StateProcess Statez A process has an execution state that indicates what it is currently doingyg Running: Executing instructions on the CPU» It is the process that has control of the CPU» How many processes can be in the running state simultaneously? Ready: Waiting to be assigned to the CPU» Ready to execute, but another process is executing on the CPU Waiting: Waiting for an event, e.g., I/O completion»It cannot make progress until event is signaled (disk completes)January 16, 2007 CSE 120 – Lecture 3 – Processes 6»It cannot make progress until event is signaled (disk completes)z As a process executes, it moves from state to state Unix “ps”: STAT column indicates execution state What state do you think a process is in most of the time? How many processes can a system support?4Process State GraphProcess State GraphCreate ProcessNew ReadyWaitingProcessI/O DoneSchedule ProcessUnschedule ProcessJanuary 16, 2007 CSE 120 – Lecture 3 – Processes 7RunningTerminatedProcess ExitI/O, Page Fault, etc.Process Data StructuresProcess Data StructuresHow does the OS represent a process in the kernel?zAt any time there are many processes in the systemzAt any time, there are many processes in the system, each in its particular statez The OS data structure representing each process is called the Process Control Block (PCB)z The PCB contains all of the info about a processz The PCB also is where the OS keeps all of a process’ January 16, 2007 CSE 120 – Lecture 3 – Processes 8hardware execution state (PC, SP, regs, etc.) when the process is not running This state is everything that is needed to restore the hardware to the same configuration it was in when the process was switched out of the hardware5PCB Data StructurePCB Data Structurez The PCB contains a huge amount of information in one large structureone large structure» Process ID (PID)» Execution state» Hardware state: PC, SP, regs» Memory management» Scheduling» Accounting»Pointers for state queuesJanuary 16, 2007 CSE 120 – Lecture 3 – Processes 9»Pointers for state queues» Etc.z It is a heavyweight abstractionstruct proc (Solaris)struct proc (Solaris)/** One structure allocated per active process. It contains all* data needed about the process while the process may be swapped* out. Other per-process data (user.h) is also inside the proc structure.* Lightweight-process data (lwp.h) and the kernel stack may be swapped out.*/*p_pglink; /* process group hash chain link next */struct proc *p_ppglink; /* process group hash chain link prev */struct sess *p_sessp; /* session information */struct pid *p_pidp; /* process ID info */struct pid *p_pgidp; /* process group ID info *//**/typedef struct proc {/** Fields requiring no explicit locking*/struct vnode *p_exec; /* pointer to a.out vnode */struct as *p_as; /* process address space pointer */struct plock *p_lockp; /* ptr to proc struct's mutex lock */kmutex_t p_crlock; /* lock for p_cred */struct cred *p_cred; /* process credentials *//** Fields protected by pidlock*/int p_swapcnt; /* number of swapped out lwps */char p_stat; /* status of process */char p_wcode; /* current wait code */ushort_t p_pidflag; /* flags protected only by pidlock */int p_wdata; /* current wait return value */pid_t p_ppid; /* process id of parent *//** Fields protected by p_lock*/kcondvar_t p_cv; /* proc struct's condition variable */kcondvar_t p_flag_cv;kcondvar_t p_lwpexit; /* waiting for some lwp to exit */kcondvar_t p_holdlwps; /* process is waiting for its lwps *//* to to be held. */ushort_t p_pad1; /* unused */uint_t p_flag; /* protected while set. *//* flags defined below */clock_t p_utime; /* user time, this process */clock_t p_stime; /* system time, this process */clock_t p_cutime; /* sum of children's user time */clock_t p_cstime; /* sum of children's system time */caddr_t *p_segacct; /* segment accounting
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