CS162 Operating Systems and Systems Programming Lecture 4 Cooperating Threads February 4 2008 Prof Anthony D Joseph http inst eecs berkeley edu cs162 Review Per Thread State Each Thread has a Thread Control Block TCB 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 OS Keeps track of TCBs in protected memory Head Link Link Link InTail Arrays or Linked Lists Registers or Registers Ready Queue 2 4 08 Other State TCB9 Other State TCB6 Joseph CS162 UCB Spring 2008 Registers Other State TCB16 Lec 4 2 Review Yielding through Internal Events Blocking on I O The act of requesting I O implicitly yields the CPU Waiting on a signal from other thread Thread asks to wait and thus yields the CPU 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 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 3 Review Stack for Yielding Thread yield Trap to OS kernel yield run new thread switch Stack growth ComputePI 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 2 4 08 Save anything next thread may trash PC regs stack Maintain isolation for each thread Joseph CS162 UCB Spring 2008 Lec 4 4 Review Two Thread Yield Example 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 Suppose we have 2 threads Threads S and T 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 5 Goals for Today More on Interrupts Thread Creation Destruction Cooperating Threads Note Some slides and or pictures in the following are adapted from slides 2005 Silberschatz Galvin and 2 4 08 Josephgenerated CS162 UCB Spring Lec 4 6 Gagne Many slides Gagne from2008 my lecture notes Interrupt Controller Priority Encoder Interrupt Mask Timer Network Software Interrupt IntID Interrupt CPU Int Disable Control 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 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 7 d ts Raise priority e n de I v a ll o Reenable All Ints s A M Save registers add r1 r2 r3 C P bl e o r subi r4 r1 4 Dispatch to Handler s i a v slli r4 r4 2 is D per Transfer Network u Packet from hardware Pipeline Flush S lw lw add sw Re r2 0 r4 U st se o r3 4 r4 r re M P r2 r2 r3 od C 8 r4 r2 e to Kernel Buffers Restore registers Clear current Int Disable All Ints Restore priority RTI Interrupt Handler External Interrupt Example Network Interrupt 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 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 8 software at priority switching boundaries Review Preemptive Multithreading Some Routine Interrupt TimerInterrupt run new thread switch Stack growth Use the timer interrupt to force scheduling decisions 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 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 9 Review Lifecycle of a Thread or Process As a thread executes it changes state 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 Active threads are represented by their TCBs TCBs organized into queues based on their state 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 10 ThreadFork Create a New Thread 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 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 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 11 How do we initialize TCB and Stack 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 Stack growth ThreadRoot stub Initial Stack 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 12 Administrivia Information about Subversion on Handouts page Make sure to take a look Other things on Handouts page Synchronization examples Interesting papers Previous finals solutions Sections in this class are mandatory Make sure that you go to the section that you have been assigned Sections will be up off the home page Make sure to respond to Barret if he contacts you He is attempting to fix section assignments Reader still TBA Should be reading Nachos code by now Start working on the first project Set up regular meeting times with your group Try figure out group interaction problems early on 2 4 08 Joseph CS162 UCB Spring 2008 Lec 4 13 How does Thread get started Other Thread Stack growth ThreadRoot 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 2 4 08 This reallyJoseph CS162 UCB Spring 2008 starts the new thread Lec 4 14 What does ThreadRoot look like ThreadRoot is the root for the thread routine Startup Housekeeping Includes things like recording start time of thread Other Statistics ThreadRoot Thread Code Stack will grow and shrink Running Stack with execution of thread Final return from thread returns into ThreadRoot which calls ThreadFinish Stack growth ThreadRoot DoStartupHousekeeping UserModeSwitch enter user mode Call fcnPtr
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