Chapter 4 Threads. Process A. Thread2 Thread ID (TID) PC Register Set Stack. Code Section Data Section Open Files

Size: px

Start display at page:

Download "Chapter 4 Threads. Process A. Thread2 Thread ID (TID) PC Register Set Stack. Code Section Data Section Open Files"

Brent York
6 years ago
Views:

1 Chapter 4 Threads Thread f Cntrl -- Fundamental Unit f CPU Utilizatin Prcess A Thread1 Thread ID (TID) PC Register Set Stack Thread2 Thread ID (TID) PC Register Set Stack Thread3 Thread ID (TID) PC Register Set Stack Cde Sectin Data Sectin Open Files Signals Single Threaded Prcess Traditinal Prcess versus Multithreaded Prcess Heavyweight Prcess 1:30 Fr each new prcess created by a single threaded prcess t service a need, a Slaris Operating System using a multithreaded prcess can create 30 new threads t serve as many new needs. Als fe each cntext-switch between prcesses, Slaris can cntext-switch between 5 threads. Mst mdern perating system kernels are multithreaded; each kernel thread perfrms a specific task, e.g., Slaris uses a set f threads t supprt interrupt handling. Als Linux uses a thread t manage free memry, i.e., keep track f all f the free memry available. Benefits Respnsiveness even if a tread is suspended, e.g., I/O request, r perfrming a very lng peratin, e.g., lading an image, the ther threads and hence the prcess, may keep running Resurce Sharing all the threads in a prcess share the same address space prvided by the prcess Prcesses nly share resurces via external techniques, such as memry sharing, messages & pipes Ecnmy -- avid additinal and unnecessary memry allcatin resurce allcatins prcess cntext-switching Scalability a Multithreaded Prcess running n a Multiprcessr Architecture threads frm ne prcess can run n mre than ne prcessr

2 Multicre Prgramming -- O/S cnsiders each cre t be a separate prcessr Cncurrency Single cre executin f threads will be interleaved ver time Multiple cres system can assign a separate thread t each cre the threads can run simultaneusly Prgramming Requirements divide activities int separate, cncurrent tasks balance tasks t ensure that they d wrk f equal value data accessed by, and pssibly mdified by, the separate tasks must be segregated int separate bundles t be run n the separate cres if data assigned t ne task is used by anther task, the executin f the tasks must be synchrnized t accmmdate the data dependency prgram running in parallel n multiple cres many different executin paths testing & debugging prcedures and techniques must be reevaluated fr effectiveness User threads prvided & managed at the user level withut kernel invlvement Kernel threads prvided & managed by the O/S Windws XP Linux Mac OS/X Slaris supprt kernel threads Many-T-One Mdel maps many user threads t ne kernel thread thread library in user space prvides thread management -- efficient thread makes a blcking call prcess is blcked nly ne thread can access the kernel at a time multiple threads cannt run in parallel n multiprcessrs GNU Prtable Threads implements the many-t-ne mdel Slaris prvides tw different methds t implement threads, ne f which is the Green Treads Library which implements the many-t- ne mdel

3 One-T-One Mdel maps each user thread t a separate kernel thread thread makes a blcking call prcess is nly blcked if it is a single threaded prcess, r all the ther threads are als blcked allws multiple threads frm ne prcess t run n multiple prcessrs creating a USER THREAD requires creating A KERNEL THREAD creating kernel threads burdens the applicatin perfrmance mst implementatins f the ne-t-ne mdel restrict the number f kernel threads Linux implements the ne-t-ne mdel; Windws als implements the ne-t-ne mdel Slaris supprts the ne-t-ne mdel as well as the ne-t-many mdel via the Green Treads Library Many-t-Many Mdel multiplexes many user threads t an equal r smaller set f kernel threads number f kernel threads may be specific t particular applicatin r particular machine number f user threads created is nt limited crrespnding kernel threads may run in parallel n multiprcessrs thread perfrms blcking system call kernel can schedule anther thread frm the same prcess prcess des nt blck prcess cntext-switch is nt required Tw-Level Mdel variatin f the many-t-many mdel multiplexes many user threads t an equal r smaller set f kernel threads allws the binding f a user thread t a kernel thread Implemented in IRIX, HP-UX, Tru-64 UNIX

4 Thread Libraries prvide API s fr creating & managing threads Implementatin User-space Library n kernel supprt library prgrams and data structures reside in user space invking a functin in the API results in a LOCAL FUNCTION CALL t user space Kernel-level Library supprted directly by the O/S library prgrams and data structures reside in kernel space invking a functin in the API fr the library results in a SYSTEM CALL t the kernel POSIX Pthreads may be implemented as either a user level library r a kernel level library Slaris, Linux, Mac OS/X, Tru64 Unix Win32 Tread Library is a kernel level library available nly n Windws Operating Systems Java Tread Library allws threads t be created and managed directly in Java prgrams; but the JVM runs either n a special Java chip r n tp f the hst O/S hence the Java Tread API generally implemented using the hst system thread library Win32 API fr a Windws Hst System Pthreads fr a Unix, Linux r Mac OS/X Hst System Cmparisn f the fllwing Tread libraries -- cmputatin f sum as indicated belw:

5 Pthreads POSIX Standard (IEEE c) Specificatin Implementatin is left t the discretin f the develpers /** Mst Unix/Linux/OS X users * gcc thrd.c -lpthread *Slaris users must enter * gcc thrd.c -lpthreads * * Figure 4.9 Gagne, Galvin, Silberschatz * Operating System Cncepts 8 th Ed. * Cpyright Jhn Wiley & Sns */ #include <pthread.h> #include <stdi.h> int sum; /* this data is shared by the thread(s) */ vid *runner(vid *param); /* the thread */ int main(int argc, char *argv[]) /* CREATES A SINGLE THREAD FOR THE MAIN FUNCTION */ pthread_t tid; /* the thread identifier */ pthread_attr_t attr; /* set f attributes fr the thread STACK SIZE, SCHEDULING INFORMATION, etc */ if (argc!= 2) fprintf(stderr,"usage: a.ut <integer value>\n"); /*exit(1);*/ return -1; if (ati(argv[1]) < 0) fprintf(stderr,"argument %d must be nn-negative\n",ati(argv[1])); /*exit(1);*/ return -1; /* get the default attributes */ pthread_attr_init(&attr); /* &attr retrieves default attributes; ptrhead_attr_init(&attr) sets attributes */ /* create the thread */ pthread_create(&tid,&attr,runner,argv[1]); /* CREATES A SECOND THREAD */ /* nw wait fr the thread t exit */ pthread_jin(tid,null); printf("sum = %d\n",sum); /The thread will begin cntrl in this functin vid *runner(vid *param) int i, upper = ati(param); sum = 0; if (upper > 0) fr (i = 1; i <= upper; i++) sum += i; pthread_exit(0); name f the prcedure r functin where the new thread will begin executin argv[1] parameter passed n the cmmand line the main thread utputs the cmputed value causes parent thread t wait fr secnd thread t terminate, i.e., execute the pthread_exit(0) cmmand

6 Win32 Threads /** This prgram creates a separate thread using the CreateThread() system call. *Figure 4.10 Gagne, Galvin, Silberschatz * Operating System Cncepts - Eighth Editin * Cpyright Jhn Wiley & Sns */ #include <stdi.h> #include <windws.h> DWORD Sum; /* glbal declaratin f data t be shared by the thread(s) unsigned 32-bit integer */ /* the thread runs in this separate functin */ DWORD WINAPI Summatin(PVOID Param) DWORD Upper = *(DWORD *)Param; fr (DWORD i = 0; i <= Upper; i++) Sum += i; return 0; Prcedure r functin t be executed by the secnd thread int main(int argc, char *argv[]) DWORD ThreadId; /* unique id fr the thread thrughut the /s */ HANDLE ThreadHandle; /* a reference t a kernel thread structure */ int Param; // d sme basic errr checking if (argc!= 2) fprintf(stderr,"an integer parameter is required\n"); return -1; Param = ati(argv[1]); if (Param < 0) fprintf(stderr, "an integer >= 0 is required \n"); return -1; thread attributes security infrmatin, stack size, flag indicating whether t start in a suspended state r make it eligible fr the CPU (shrt-term) scheduler. Default attributes make the thread eligible fr the scheduler. creates secnd thread // create the thread ThreadHandle = CreateThread(NULL, 0, Summatin, &Param, 0, &ThreadId); if (ThreadHandle!= NULL) WaitFrSingleObject(ThreadHandle, INFINITE); ClseHandle(ThreadHandle); printf("sum = %d\n",sum); causes the main thread t wait fr the secnd threads terminatin main thread then utputs the result f the cmputatin perfrmed by the secnd thread

7 Java Threads Java supprts tw independent prcedures fr creating Java threads create a new class derived frm the Thread class and verride its run( ) methd define a class that implements the Runnable interface /**This prgram creates a separate thread by implementing the Runnable interface. * Figure 4.11 Gagne, Galvin, Silberschatz Operating System Cncepts - 8 th Ed. * Cpyright Jhn Wiley & Sns */ class Sum private int sum; public int get() return sum; public vid set(int sum) this.sum = sum; Java shares data between the main thread in the Driver (main) class and the wrker thread in the Summatin class via the Sum class which includes an accessr methd, i.e., get( )methd, and a mutatr methd, i.e., set( ) methd, fr just such a purpse. class Summatin implements Runnable private int upper; private Sum sumvalue; Summatin(int upper, Sum sumvalue) if (upper < 0) thrw new IllegalArgumentExceptin(); this.upper = upper; this.sumvalue = sumvalue; public interface Runnable public abstract vid run( ); definitin f Summatin cnstructr public vid run() int sum = 0; fr (int i = 0; i <= upper; i++) sum += i; sumvalue.set(sum); public class Driver public static vid main(string[] args) first thread created if (args.length!= 1) System.err.println("Usage Driver <integer>"); System.exit(0); run( ) verrides the default run( ) methd, e.g., Runnable interface run( ) start( ) methd executin allcates memry in kernel space initializes the new thread in the kernel calls the run methd directly, hence making the thread eligible t be run in the JVM Java user cde never directly calls the run( ) methd Sum sumobject = new Sum(); int upper = Integer.parseInt(args[0]); secnd thread defined Thread wrker = new Thread(new Summatin(upper, sumobject)); wrker.start(); secnd thread created & started try wrker.jin(); main thread waits fr the terminatin f the secnd thread catch (InterruptedExceptin ie) System.ut.println("The sum f " + upper + " is " + sumobject.get()); first thread utputs the value

8 Thread Issues if a single thread in multithreaded prcess issues frk( ) system call, shuld the new prcess duplicate all the threads f the parent prcess and thus be multithreaded r duplicate nly the single thread and thus be single threaded thread cancellatin asynchrnus cancellatin dwnlading images n the web may leave sme resurces un-reclaimed deferred cancellatin synchrnus cancellatin ntice issued f target thread cancellatin, e.g., cancellatin flag is set cancellatin ccurs after target thread checks the cancellatin flag check is perfrmed at cancellatin pint cancellatin pint pint f executin where thread may be safely cancelled Signals Synchrnus Signals prcess peratin causes signal signal delivered t the prcess Asynchrnus Signals signal generated by an event external t the running prcess Signal Handlers Default User Defined Tw Versins f frk( ) Linux e.g., ne versin duplicates nly the thread that invked the frk( ) call the ther duplicates all the threads f the parent prcess Multithreaded Prcesses deliver the signal t the thread t which the signal applies every thread in the prcess a specified set f threads designated thread that handles all signals fr the prcess Unix allw threads t blck signals signal is delivered t the first thread nt blcking it cmmand delivering a Unix signal kill(pid_t tid, int signal) Windws Asynchrnus Prcedure Calls (APC) user thread specifies a functin t call when the user thread receives ntificatin f a particular event ntificatin delivered t a particular thread via the functin

9 Thread Pls limit the ttal number f threads in system at any ne time service requests with existing threads frm the thread pl eliminate cnstant thread creatin & deletin verhead when pl is empty, stack incming thread requests; service thse requests as threads becme available dynamically adjust the number f threads in the pl depending upn traffic demands Thread Specific Data ne transactin ne transactin identifier ne set f transactin data ne thread Scheduler Activatins Many-t-Many Mdel Tw-Level Mdel -- binding user thread t kernel thread Light Weight Prcess LWP User library LWP is virtual prcessr, i.e., user library can schedule user threads n the LWP each LWP is attached t a kernel tread If the kernel thread blcks LWP blck user thread blcks efficient executin requires that there be ne LWP fr each ptential, cncurrent blcking call kernel prvides t each prcess a set f LWP s each prcess schedules threads n any available LWP in the set Upcall kernel infrms the prcess abut certain events, e.g., impending blcks f specific thread Upcall Handler allcates a new LWP t the prcess saves the state f the blcking thread schedules an eligible thread t run n the new LWP, hence it allws the prcess t cntinue when the blcking event ends, an upcall is made t the thread library infrming it that the thread is nw eligible t run allcates anther new LWP t the prcess prcess can schedule an eligible thread t execute

10 Windws XP Threads Win32 API One-t-One Mdel Fiber Library functinality f the Many-t-Many Mdel Thread Cmpnents tid register set prcessr status user stack used when thread is in user mde kernel stack used when thread is in kernel mde private strage area private data used by run-time libraries dynamic link libraries DLL thread cntext Thread Data Structures Executive Thread Blck Kernel Thread Blck Thread Envirnmental Blck ETHREAD thread start address Pinter t parent prcess KTHREAD scheduling & synchrnizatin infrmatin kernel stack TEB thread identifier user stack thread lcal strage kernel space user space

11 Linux Threads task prcess thread frk( ) creates new prcess clne( ) creates new entity which varies between a new prcess and a new thread flags CLONE_FS share file-system infrmatin CLONE_VM share memry space CLONE_SIGHAND share signal handlers CLONE_FILES share pen files all flags set new prcess is created n flags set new thread is created task data structure, i.e., struct task_struct struct task_struct pen files signal handling infrmatin virtual memry etc pen files virtual memry signal handling infrmatin frk( ) create new task data structure, i.e., struct task_struct cpy all data frm riginal structure t new structure create new structures fr pen files, signal handling infrmatin, virtual memry cpy infrmatin frm ld structures t the new structures clne( ) create new task data structure, i.e., struct task_struct depending upn what flags are set, use pinters in the new task structure t reference the ld structures create new structures cpy the data frm the ld structures t the new structures set the task pinters t reference the new structures Native POSIX Thread Library (NPTL) POSIX-cmpliant Thread Mdel thread creatin cheaper than task creatin

Operating systems. Module 7 IPC (Interprocess communication) PART I. Tami Sorgente 1

Operating systems. Module 7 IPC (Interprocess communication) PART I. Tami Sorgente 1 Operating systems Mdule 7 IPC (Interprcess cmmunicatin) PART I Tami Srgente 1 INTERPROCESS COMMUNICATION Prcesses within a system may be independent r cperating Cperating prcess can affect r be affected