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Chapter 4: Threads

Chapter 4: Threads. Typical Program. Processor utilization?. Without Kernel Support. Why discuss in an OS course Without kernel support: Responsibility on the process Requires a thread manager compiled as part of each multithreaded process Appears single-threaded to OS

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Chapter 4: Threads

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  1. Chapter 4: Threads

  2. Typical Program • Processor utilization?

  3. Without Kernel Support • Why discuss in an OS course • Without kernel support: • Responsibility on the process • Requires a thread manager • compiled as part of each multithreaded process • Appears single-threaded to OS • Responsibilities of thread manager • Primary control of the process • Determines • Which thread to execute • When to switch to another thread Threads Thread Manager Operating System

  4. Conceptually, no kernel support is many-to-one Many user-level threads mapped to single kernel thread Examples: Solaris Green Threads GNU Portable Threads Many-to-One Model Known as User Level Threading

  5. When an application requests I/O it is put in the waiting queue Even if thread manager suspends a thread just before an I/O request once the TM allows a single I/O request the entire process gets suspended Drawback of User Level A single I/O request from any thread causes the entire application to be suspended

  6. Kernel Support • Thread-aware kernel • Can avoid suspending a multi-threaded app on I/O • When I/O complete • Determines if process is running • Informs process of I/O completion Thread aware kernel allows for more efficient use of resources particularly for high I/O applications

  7. Kernel Threads • Idea of threads has even been extended to the OS, itself • Thread models • Many-to-One • One-to-One • Many-to-Many • OS’s that support kernel threads • Windows XP/2000 • Solaris • Linux • Tru64 UNIX • Mac OS X

  8. One-to-One • Each user-level thread maps to kernel thread • Examples • Windows NT/XP/2000 • Linux • Solaris 9 and later • Drawback: must generate a kernel thread for every user thread

  9. Many-to-Many Model • Can generate a kernel thread for each logical task • OS’s that support it • Solaris prior to version 9 • Windows NT/2000 with the ThreadFiber package

  10. Two-level Model • Similar to M:M, except that it allows a user thread to be bound to kernel thread • Examples • IRIX • HP-UX • Tru64 UNIX • Solaris 8 and earlier

  11. Thread Libraries • Three primary thread libraries: • POSIX Pthreads • Available with and without kernel • Win32 threads • Kernel support • Java threads • Kernel support depends upon host system • JVM written and compiled for each host

  12. Example • Posix threads example #include <pthread.h> pthread_tmyThread; pthread_create( &myThread, pointerToFunction); pthread_join( myThread);

  13. Parallel calculation example • Create an array of threads • Put jobs in a list • Create a thread for each job • Each thread watches a list of available servers • When a server becomes available, takes ownership of the server, and sends the job to the server • When complete, thread puts job in completed list, and puts server in available server list Completed Jobs Pending Jobs Servers

  14. End of Chapter 4

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