Review Per Thread State Each Thread has a Thread Control Block TCB CS162 Operating Systems and Systems Programming Lecture 5 Execution State CPU registers program counter pointer to stack Scheduling info State more later priority CPU time Accounting Info Various Pointers for implementing scheduling queues Pointer to enclosing process PCB Etc add stuff as you find a need Cooperating Threads OS Keeps track of TCBs in protected memory September 14 2005 Prof John Kubiatowicz http inst eecs berkeley edu cs162 In Arrays or Linked Lists or Head Tail Link Registers Other State TCB9 Ready Queue 9 14 05 Link Registers Other State TCB16 Kubiatowicz CS162 UCB Fall 2005 Review Yielding through Internal Events Lec 5 2 Review Stack for Yielding Thread ComputePI The act of requesting I O implicitly yields the CPU Trap to OS Waiting on a signal from other thread Thread asks to wait and thus yields the CPU kernel yield run new thread Thread executes a yield Thread volunteers to give up CPU computePI while TRUE ComputeNextDigit yield Note that yield must be called by programmer frequently enough Kubiatowicz CS162 UCB Fall 2005 yield Lec 5 3 switch Stack growth Blocking on I O 9 14 05 Link Registers Other State TCB6 How do we run a new thread run new thread newThread PickNewThread switch curThread newThread ThreadHouseKeeping Later in lecture How does dispatcher switch to a new thread Save anything next thread may trash PC regs stack Maintain isolation for each thread 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 4 Review Two Thread Yield Example Goals for Today proc A B proc B while TRUE yield Stack growth Consider the following code blocks Thread S Thread T A A B while B while yield yield run new thread run new thread switch switch More on Interrupts Thread Creation Destruction Cooperating Threads Suppose we have 2 threads Note Some slides and or pictures in the following are adapted from slides 2005 Silberschatz Galvin and Gagne Threads S and T Kubiatowicz CS162 UCB Fall 2005 Lec 5 5 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Example Network Interrupt Interrupt Controller Interrupt Control CPU Int Disable NMI Interrupts invoked with interrupt lines from devices Interrupt controller chooses interrupt request to honor Mask enables disables interrupts Priority encoder picks highest enabled interrupt Software Interrupt Set Cleared by Software Interrupt identity specified with ID line CPU can disable all interrupts with internal flag Non maskable interrupt line NMI can t be disabled 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 7 d ts Raise priority ve In deReenable All Ints a s o ll add r1 r2 r3 PC le A r M Save registers subi r4 r1 4 o Dispatch to Handler b s slli r4 r4 2 sa r v i i D pe Transfer Network Su Packet from hardware Pipeline Flush External Interrupt Priority Encoder Interrupt Mask Timer Network IntID Software Interrupt Lec 5 6 lw lw add sw Re r2 0 r4 Us sto r3 4 r4 er re r2 r2 r3 M PC od 8 r4 r2 e to Kernel Buffers Restore registers Clear current Int Disable All Ints Restore priority RTI Interrupt Handler 9 14 05 Disable Enable All Ints Internal CPU disable bit RTI reenables interrupts returns to user mode Raise lower priority change interrupt mask Software interrupts can be provided entirely in software at priority switching boundaries 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 8 Review Preemptive Multithreading Review Lifecycle of a Thread or Process Use the timer interrupt to force scheduling decisions TimerInterrupt run new thread switch Stack growth Some Routine Interrupt Timer Interrupt routine TimerInterrupt DoPeriodicHouseKeeping run new thread This is often called preemptive multithreading since threads are prempted for better scheduling Solves problem of user who doesn t insert yield 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 9 As a thread executes it changes state Active threads are represented by their TCBs TCBs organized into queues based on their state 9 14 05 ThreadFork Create a New Thread Kubiatowicz CS162 UCB Fall 2005 Lec 5 10 How do we initialize TCB and Stack ThreadFork is a user level procedure that creates a new thread and places it on ready queue We called this CreateThread earlier Arguments to ThreadFork Pointer to application routine fcnPtr Pointer to array of arguments fcnArgPtr Size of stack to allocate Initialize Register fields of TCB Stack pointer made to point at stack PC return address OS asm routine ThreadRoot Two arg registers initialized to fcnPtr and fcnArgPtr Initialize stack data No Important part of stack frame is in registers ra Think of stack frame as just before body of ThreadRoot really gets started Implementation Sanity Check arguments Enter Kernel mode and Sanity Check arguments again Allocate new Stack and TCB Initialize TCB and place on ready list Runnable ThreadRoot stub Stack growth new The thread is being created ready The thread is waiting to run running Instructions are being executed waiting Thread waiting for some event to occur terminated The thread has finished execution Initial Stack 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 11 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 12 Administrivia How does Thread get started Other Thread If you haven t generated a new key yet and given a passcode you must do this NOW ThreadRoot We need the ssh keys to make the group accounts Stack growth Sections in this class are mandatory Make sure that you go to the section that you have been assigned Should be reading Nachos code by now You should know enough to start working on the first project Set up regular meeting times with your group Let s try to get group interaction problems figured out early A B while yield run new thread New Thread switch ThreadRoot stub Eventually run new thread will select this TCB and return into beginning of ThreadRoot This really starts the new thread 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 13 What does ThreadRoot look like ThreadRoot DoStartupHousekeeping UserModeSwitch enter user mode Call fcnPtr fcnArgPtr ThreadFinish Includes things like recording start time of thread Other Statistics Thread Code Can t deallocate thread yet Stack will grow and shrink Running Stack with execution of thread Final return from thread returns into ThreadRoot which calls ThreadFinish ThreadFinish will start at user level 9 14 05 Kubiatowicz CS162 UCB Fall 2005 Lec 5 14 Threads like the parent may be on a wait queue waiting for this thread to finish Stack growth Startup Housekeeping Kubiatowicz CS162 UCB Fall 2005 What does
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